Light-emitting device, display device, electronic device, organic compound, and lighting device

Abstract

A multicolor light-emitting element with high luminous efficiency is provided. The light-emitting element comprises a material used as an energy donor, a fluorescent material, and a phosphorescent material in its light-emitting layer. The material used as an energy donor has the function of converting a triple excitation energy into light emission. The fluorescent material has a molecular structure comprising a light-emitting body and a protecting group, and each molecule of the guest material contains more than five protecting groups. By introducing protecting groups into the molecule, the transfer of triple excitation energy from the material used as an energy donor to the light-emitting material based on the Dexter mechanism is suppressed. Alkyl groups and branched alkyl groups are used as protecting groups. Light emission from both the fluorescent material and the phosphorescent material is obtained in this light-emitting element.

Description

Technical Field

[0001] One embodiment of the present invention relates to a light-emitting element, an organic compound, or a display device, electronic device, and lighting device that includes the light-emitting element.

[0002] Note that one embodiment of the present invention is not limited to the above-described technical field. The technical field of one embodiment of the invention disclosed in this specification relates to an object, method, or manufacturing method. Furthermore, one embodiment of the present invention relates to a process, machine, manufacture, or composition of matter. Therefore, more specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include semiconductor devices, display devices, liquid crystal display devices, light-emitting devices, lighting devices, energy storage devices, memory devices, and methods for driving or manufacturing these devices. Prior Technology

[0003] In recent years, research and development of light-emitting elements utilizing electroluminescence (EL) has become increasingly active. The basic structure of these light-emitting elements consists of a layer containing a light-emitting material (EL layer) sandwiched between a pair of electrodes. By applying a voltage between the electrodes of the element, light emission from the light-emitting material can be obtained.

[0004] Because the aforementioned light-emitting element is a self-emissive element, the display device using this element has the following advantages: good visibility; no need for backlighting; and low power consumption. Furthermore, the display device also has the following advantages: it can be manufactured to be thin and light; and it has a fast response time.

[0005] When using a light-emitting element (e.g., an organic EL element) that uses an organic compound as the luminescent material and places an EL layer containing the luminescent organic compound between a pair of electrodes, current flows through it by applying a voltage between the pair of electrodes, where electrons and holes are injected from the cathode and anode into the luminescent EL layer, respectively. Furthermore, the injected electrons and holes recombine to excite the luminescent organic compound, thus producing light emission.

[0006] As types of excited states formed by organic compounds, there are singlet excited states (S*) and triplet excited states (T*). Emission from singlet excited states is called fluorescence, and emission from triplet excited states is called phosphorescence. Furthermore, in this light-emitting element, the statistically significant ratio of singlet excited states to triplet excited states is S*:T* = 1:3. Therefore, light-emitting elements using phosphorescent compounds (phosphorescent materials) have higher luminous efficiency than those using fluorescent compounds (fluorescent materials). Consequently, in recent years, research and development of light-emitting elements using phosphorescent materials capable of converting triplet excitation energy into emission has become increasingly active.

[0007] Light-emitting elements using phosphorescent materials, especially those emitting blue light, have not yet been put into practical use due to the difficulty in developing stable compounds with high triplet excitation energy levels. Therefore, research is underway to develop light-emitting elements using more stable fluorescent materials, seeking methods to improve the luminous efficiency of these elements (fluorescent light-emitting elements).

[0008] Besides phosphorescent materials, thermally activated delayed fluorescence (TADF) materials are known as materials capable of converting part or all of the triplet excitation energy into luminescence. In TADF materials, a singlet excited state is generated from the triplet excited state through antisystem crossing, and the singlet excited state is converted into luminescence.

[0009] To improve luminescence efficiency in light-emitting elements using TADF materials, it is important not only to efficiently generate singlet excited states from triplet excited states in TADF materials, but also to efficiently obtain light emission from singlet excited states; that is, high fluorescence quantum yield is crucial. However, it is difficult to design light-emitting materials that simultaneously satisfy both of these conditions.

[0010] In addition, a method has been proposed in which the single excitation energy of the thermally activated delayed fluorescent material is transferred to the fluorescent material in a light-emitting element comprising a thermally activated delayed fluorescent material and a fluorescent material, and light emission is obtained from the fluorescent material (see Patent Document 1).

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2014-45179

[0012] [Non-Patent Literature 1] Hiroki Noda et al., “SCIENCE ADVANCES”, 2018, vol. 4, no. 6, eaao6910 [Non-Patent Literature 2] S. Wang et al., Angew. Chem., Int. Ed. 54, 13068 (2015).

[0013] Multicolor light-emitting elements, represented by white light-emitting elements, are desired for applications such as displays. As a component structure for obtaining multicolor light-emitting elements, an example is a light-emitting element with multiple EL layers separated by a charge-generating layer (also called a series element). Since materials emitting different colors can be used in different EL layers in a series element, it is suitable for manufacturing multicolor light-emitting elements. However, the large number of layers in a series element results in a high number of processing steps.

[0014] Therefore, there is a need for light-emitting elements capable of producing multiple emission colors from a single EL layer. To achieve multiple emission colors, two or more guest materials are used in the light-emitting layer; however, from a reliability standpoint, it is necessary to develop multicolor light-emitting elements using fluorescent materials.

[0015] As described above, one method for increasing the efficiency of light-emitting elements using fluorescent materials is to convert triplet excitons in the host material into singlet excitons, and then transfer the singlet excitation energy to the fluorescent material as the guest material. However, when the fluorescent material is used as the guest material in the emitting layer of the light-emitting element, the lowest triplet excitation energy level (T1 level) of the fluorescent material does not contribute to luminescence, but sometimes becomes the deactivation path of the triplet excitation energy. Therefore, it is difficult to achieve high efficiency in light-emitting elements using fluorescent materials.

[0016] Therefore, in order to improve the luminous efficiency and reliability of light-emitting elements using fluorescent materials, it is preferable that the triplet excitation energy in the light-emitting layer is efficiently converted into a singlet excitation energy and efficiently transferred to the fluorescent material as a singlet excitation energy. To this end, it is necessary to develop a method that efficiently generates a singlet excitation state of the guest material from the triplet excited state of the host material, thereby further improving the luminous efficiency and reliability of the light-emitting element. Summary of the Invention

[0017] Therefore, one embodiment of the present invention aims to provide a light-emitting element capable of obtaining multiple emitting colors from a single EL layer. Another embodiment of the present invention aims to provide a light-emitting element with high luminous efficiency. Furthermore, one embodiment of the present invention aims to provide a light-emitting element with reduced power consumption. Additionally, one embodiment of the present invention aims to provide a novel light-emitting element. Furthermore, one embodiment of the present invention aims to provide a novel light-emitting device. Finally, one embodiment of the present invention aims to provide a novel display device.

[0018] Note that the description of the above objectives does not preclude the existence of other objectives. One embodiment of the present invention does not necessarily need to achieve all of the above objectives. Furthermore, objectives other than those described above can be learned from and derived from the specification, etc.

[0019] As mentioned above, there is a need to develop a method for efficiently converting triple excitation energy into luminescence in fluorescent light-emitting elements. To this end, it is necessary to improve the energy transfer efficiency between the materials used in the light-emitting layer. This requires suppressing the transfer of triple excitation energy between the energy donor and energy acceptor based on the Dexter mechanism. Simultaneously, it is necessary to develop light-emitting elements capable of efficiently obtaining multicolor luminescence.

[0020] Therefore, one embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes. The light-emitting layer comprises a first material having the function of converting a triple excitation energy into light emission, a second material having the function of converting a single excitation energy into light emission, and a third material having the function of converting a triple excitation energy into light emission. The second material comprises a light-emitting element and five or more protecting groups. The light-emitting element is a fused aromatic ring or a fused heteroaromatic ring. Each of the five or more protecting groups independently comprises any one of an alkyl group having 1 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, or a trialkylsilyl group having 3 or more but less than 12 carbon atoms. The lowest triple excitation energy level (T1 energy level) of the first material is higher than the T1 energy level of the third material. The light-emitting element obtains light emission from both the second and third materials.

[0021] In the above structure, preferably, at least four of the five or more protecting groups are each independently one of an alkyl group having 3 or more and 10 or less carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more and 10 or less carbon atoms, or a trialkylsilyl group having 3 or more and 12 or less carbon atoms.

[0022] Another embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes. The light-emitting layer comprises a first material having the function of converting a triple excitation energy into light emission, a second material having the function of converting a single excitation energy into light emission, and a third material having the function of converting a triple excitation energy into light emission. The second material comprises a light-emitting element and four protecting groups. The light-emitting element is a fused aromatic ring or a fused heteroaromatic ring. The four protecting groups are not directly bonded to the fused aromatic ring or the fused heteroaromatic ring. Each of the four protecting groups independently comprises one of an alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, or a trialkylsilyl group having 3 or more but less than 12 carbon atoms. The T1 energy level of the first material is higher than that of the third material. The light-emitting element obtains light from both the second and third materials.

[0023] Another embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes. The light-emitting layer comprises a first material having the function of converting triple excitation energy into light emission and a second material having the function of converting single excitation energy into light emission. The second material comprises a light-emitting element and two or more diarylamine groups. The light-emitting element is a fused aromatic ring or a fused heteroaromatic ring. The fused aromatic ring or fused heteroaromatic ring is bonded to two or more diarylamine groups, each of which independently has at least one protecting group. The protecting group independently comprises any one of an alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, or a trialkylsilyl group having 3 or more but less than 12 carbon atoms. The light-emitting element emits light from both the first material and the second material.

[0024] Another embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes. The light-emitting layer comprises a first material having the function of converting a triple excitation energy into light emission, a second material having the function of converting a single excitation energy into light emission, and a third material having the function of converting a triple excitation energy into light emission. The second material comprises a light emitter and two or more diarylamine groups. The light emitter is a fused aromatic ring or a fused heteroaromatic ring. The fused aromatic ring or fused heteroaromatic ring is bonded to two or more diarylamine groups, each of which independently has at least two protecting groups. Each protecting group independently comprises one of an alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, or a trialkylsilyl group having 3 or more but less than 12 carbon atoms. The T1 energy level of the first material is higher than that of the third material. The light-emitting element obtains light from both the second and third materials.

[0025] In addition, in the above structure, the diarylamine group is preferably a diphenylamine group.

[0026] In addition, in the above structure, the alkyl group is preferably a branched alkyl group.

[0027] Another embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes. The light-emitting layer comprises a first material having the function of converting a triple excitation energy into light emission, a second material having the function of converting a single excitation energy into light emission, and a third material having the function of converting a triple excitation energy into light emission. The second material comprises a light-emitting element and a plurality of protecting groups. The light-emitting element is a fused aromatic ring or a fused heteroaromatic ring. At least one of the atoms constituting the plurality of protecting groups is located directly on one face of the fused aromatic ring or the fused heteroaromatic ring. At least one of the atoms constituting the plurality of protecting groups is located directly on the other face of the fused aromatic ring or the fused heteroaromatic ring. The T1 energy level of the first material is higher than that of the third material. The light-emitting element obtains light from both the second and third materials.

[0028] Another embodiment of the present invention is a light-emitting element comprising a light-emitting layer between a pair of electrodes. The light-emitting layer comprises a first material having the function of converting a triple excitation energy into light emission, a second material having the function of converting a single excitation energy into light emission, and a third material having the function of converting a triple excitation energy into light emission. The second material comprises a light emitter and two or more diphenylamino groups. The light emitter is a fused aromatic ring or a fused heteroaromatic ring. The fused aromatic ring or fused heteroaromatic ring is bonded to two or more diphenylamino groups, and the phenyl groups in the two or more diphenylamino groups each have protecting groups independently at the 3- and 5-positions. The protecting groups each independently have one of the following: an alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, or a trialkylsilyl group having 3 or more but less than 12 carbon atoms. The T1 energy level of the first material is higher than that of the third material. The light-emitting element obtains light from both the second and third materials.

[0029] In addition, in the above structure, the alkyl group is preferably a branched alkyl group.

[0030] In addition, in the above structure, the branched alkyl group preferably contains a quaternary carbon.

[0031] In addition, in the above structure, the fused aromatic ring or fused heteroaromatic ring preferably includes at least one of naphthalene, anthracene, fumonisin, chrysene, triphenylene, tetraphenylene, pyrene, perylene, coumarin, quinacridone, and naphthobisbenzofuran.

[0032] Furthermore, in the above structure, preferably, the first material comprises a first organic compound and a second organic compound, and the first organic compound and the second organic compound form an excited-state complex. More preferably, the first organic compound exhibits phosphorescence.

[0033] Furthermore, in the above structure, the peak wavelength of the emission spectrum of the first material is preferably closer to the shorter wavelength side than the peak wavelength of the emission spectrum of the second material.

[0034] In addition, in the above structure, the first material is preferably a compound that exhibits phosphorescence or delayed fluorescence.

[0035] In addition, in the above structure, the emission spectrum of the first material preferably overlaps with the absorption band on the longest wavelength side of the absorption spectrum of the second material.

[0036] In addition, in the above structure, the concentration of the second material in the light-emitting layer is preferably higher than the concentration of the third material.

[0037] In addition, in the above structure, the third material is preferably a compound that exhibits phosphorescence.

[0038] Furthermore, in the above structure, the peak wavelength of the emission spectrum of the second material is preferably closer to the shorter wavelength side than the peak wavelength of the emission spectrum of the third material.

[0039] Another embodiment of the present invention is a display device comprising at least one of the light-emitting elements with the above-described structures, and a color filter and a transistor. Another embodiment of the present invention is an electronic device comprising at least one of the above-described display device, and a housing and a touch sensor. Another embodiment of the present invention is a lighting device comprising at least one of the light-emitting elements with the above-described structures, and a housing and a touch sensor. Furthermore, one embodiment of the present invention includes not only light-emitting devices with light-emitting elements but also electronic devices with light-emitting devices. Therefore, in this specification, a light-emitting device refers to an image display device or a light source (including lighting devices). Additionally, a light-emitting device sometimes includes modules such as: a display module with connectors such as FPC (Flexible Printed Circuit) or TCP (Tape Carrier Package) mounted on the light-emitting element; a display module with a printed circuit board provided at the TCP end; or a display module in which an IC (Integrated Circuit) is directly mounted on the light-emitting element via COG (Chip On Glass).

[0040] According to one embodiment of the present invention, a light-emitting element capable of obtaining multiple emission colors from a single EL layer can be provided. According to one embodiment of the present invention, a light-emitting element with high luminous efficiency can be provided. Furthermore, according to one embodiment of the present invention, a light-emitting element with reduced power consumption can be provided. Furthermore, according to one embodiment of the present invention, a novel light-emitting element can be provided. Furthermore, according to one embodiment of the present invention, a novel light-emitting device can be provided. Furthermore, according to one embodiment of the present invention, a novel display device can be provided.

[0041] Note that the description of these effects does not preclude the existence of other effects. Furthermore, an embodiment of the present invention does not necessarily require all of the aforementioned effects. Additionally, effects other than those described above can be learned from and derived from the specification, drawings, claims, etc. Simple Explanation of the Diagram

[0042] In the diagram: Figures 1A and 1B are schematic cross-sectional views of the light-emitting layer of a light-emitting element according to an embodiment of the present invention, and Figure 1C is a diagram illustrating the energy level correlation of the light-emitting layer of a light-emitting device according to an embodiment of the present invention. Figure 2A is a schematic diagram of a conventional object material, and Figure 2B is a schematic diagram of an object material for a light-emitting element used in one embodiment of the present invention. Figure 3A is a structural formula of the guest material used in the light-emitting element according to one embodiment of the present invention, and Figure 3B is a ball-and-stick diagram of the guest material used in the light-emitting element according to one embodiment of the present invention. Figure 4A is a cross-sectional schematic diagram of the light-emitting layer of a light-emitting element according to an embodiment of the present invention, and Figures 4B to 4D are diagrams illustrating the energy level correlation of the light-emitting layer of a light-emitting device according to an embodiment of the present invention; Figure 5A is a cross-sectional schematic diagram of the light-emitting layer of a light-emitting element according to an embodiment of the present invention; Figures 5B and 5C are diagrams illustrating the energy level correlation of the light-emitting layer of a light-emitting device according to an embodiment of the present invention. Figure 6 is a cross-sectional schematic diagram of a light-emitting element according to one embodiment of the present invention; Figure 7A is a top view illustrating a display device according to an embodiment of the present invention, and Figure 7B is a cross-sectional schematic diagram illustrating a display device according to an embodiment of the present invention. Figures 8A and 8B are schematic cross-sectional views illustrating a display device according to one embodiment of the present invention; Figures 9A and 9B are schematic cross-sectional views illustrating a display device according to one embodiment of the present invention; Figures 10A to 10D are perspective views illustrating a display module according to one embodiment of the present invention; Figures 11A to 11C are diagrams illustrating an electronic device according to one embodiment of the present invention; Figures 12A and 12B are perspective views illustrating a display device according to one embodiment of the present invention; Figure 13 is a diagram illustrating a lighting device according to one embodiment of the present invention; Figure 14 is a graph illustrating the external quantum efficiency-luminance characteristics of the light-emitting element according to an embodiment; Figure 15 is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to an embodiment; Figure 16 is a graph illustrating the relationship between the electroluminescence spectrum of the light-emitting element, the absorption spectrum of the compound, and the emission spectrum according to the embodiment; Figure 17 is a graph illustrating the external quantum efficiency-luminance characteristics of the light-emitting element according to an embodiment; Figure 18 is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to an embodiment; Figure 19 is a diagram illustrating the chromaticity-luminance characteristics of the light-emitting element according to an embodiment; Figure 20 is a graph illustrating the reliability test results of the light-emitting element according to the embodiment; Figure 21 is a graph illustrating the electroluminescence spectrum of the light-emitting element before and after a reliability test according to an embodiment; Figures 22A and 22B illustrate the NMR spectra of the compounds according to the reference example; Figure 23 is an illustration of the NMR spectrum of the compound according to the reference example; Figures 24A and 24B are illustrations of the NMR spectra of the compounds according to the reference example; Figure 25 shows the NMR spectrum of the compound according to the reference example; Figure 26 is a graph illustrating the external quantum efficiency-luminance characteristics of the light-emitting element according to an embodiment; Figure 27 is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to an embodiment; Figure 28 is a graph illustrating the external quantum efficiency-luminance characteristics of the light-emitting element according to an embodiment; Figure 29 is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to an embodiment; Figures 30A and 30B are illustrations of the NMR spectra of the compounds according to the reference example; Figure 31 is a diagram illustrating the NMR spectrum of the compound according to the reference example. The selected figures for this invention are Figures 2A and 2B. Implementation

[0043] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following description, and its methods and details can be varied in various forms without departing from the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited only to the contents described in the embodiments shown below.

[0044] Furthermore, for ease of understanding, the positions, sizes, and extents of various structures shown in drawings, etc., do not necessarily represent their actual positions, sizes, and extents. Therefore, the disclosed invention is not necessarily limited to the positions, sizes, and extents disclosed in the drawings, etc.

[0045] Furthermore, in this specification and other documents, ordinal numbers such as "first," "second," etc., are added for ease of understanding, but these do not always indicate the process sequence or stacking order. Therefore, for example, "first" can be appropriately replaced with "second" or "third," etc., for description. In addition, the ordinal numbers described in this specification and other documents are sometimes inconsistent with the ordinal numbers used to specify one embodiment of the present invention.

[0046] Note that in this specification and the like, when the structure of the invention is illustrated using drawings, symbols representing the same parts are sometimes used in common in different drawings.

[0047] Additionally, in this specification and other materials, the terms "film" and "layer" may be interchanged. For example, "conductive layer" may sometimes be replaced with "conductive film." Also, "insulating film" may sometimes be replaced with "insulating layer."

[0048] Furthermore, in this specification, a singlet excited state (S*) refers to a singlet state having an excitation energy. The S1 level is the lowest level of the singlet excitation energy levels, referring to the excitation energy level of the lowest singlet excited state (S1 state). A triplet excited state (T*) refers to a triplet state having an excitation energy. The T1 level is the lowest level of the triplet excitation energy levels, referring to the excitation energy level of the lowest triplet excited state (T1 state). Although sometimes only "singlet excited state" and "singlet excitation energy level" are used in this specification, they sometimes represent the S1 state and the S1 level, respectively. Even when referred to as "triple excited state" and "triple excitation energy level," they sometimes represent the T1 state and the T1 level, respectively.

[0049] Furthermore, in this specification, fluorescent materials refer to compounds that emit light in the visible light region when returning from a singlet excited state to the ground state. Phosphorescent materials refer to compounds that emit light in the visible light region at room temperature when returning from a triplet excited state to the ground state. In other words, phosphorescent materials refer to compounds capable of converting triplet excitation energy into visible light.

[0050] Note that in this instruction manual, room temperature refers to a temperature range of 0°C to 40°C.

[0051] Furthermore, in this specification, the blue wavelength region refers to the wavelength region of 400 nm or more and less than 490 nm, in which blue emission has at least one emission spectral peak. Similarly, the green wavelength region refers to the wavelength region of 490 nm or more and less than 580 nm, in which green emission has at least one emission spectral peak. Finally, the red wavelength region refers to the wavelength region of 580 nm or more and less than 680 nm, in which red emission has at least one emission spectral peak. Moreover, even when two emission spectra each have emission spectral peaks in the same wavelength region, if the peak wavelengths are different, it is sometimes considered that the two emission spectra have different emission colors. Note that the emission spectral peak is a maximum value, or may include a shoulder peak.

[0052] Implementation Method 1 In this embodiment, a light-emitting element according to one embodiment of the present invention will be described with reference to FIGS. 1A to 5C.

[0053] <Structure Examples of Light-Emitting Elements> First, the structure of a light-emitting element according to an embodiment of the present invention will be described below with reference to Figures 1A to 1C.

[0054] Figure 1A is a cross-sectional schematic diagram of a light-emitting element 150 according to an embodiment of the present invention.

[0055] The light-emitting element 150 includes a pair of electrodes (electrode 101 and electrode 102) and an EL layer 100 disposed between the pair of electrodes. The EL layer 100 includes at least a light-emitting layer 130.

[0056] In addition, the EL layer 100 shown in Figure 1A includes functional layers such as hole injection layer 111, hole transport layer 112, electron transport layer 118, and electron injection layer 119, in addition to the light-emitting layer 130.

[0057] Note that although this embodiment describes electrode 101 as the anode and electrode 102 as the cathode, the structure of the light-emitting element 150 is not limited to this. That is, electrode 101 can also be used as the cathode and electrode 102 as the anode, and the order of the layers between the electrodes can be reversed. In other words, the hole injection layer 111, hole transport layer 112, light-emitting layer 130, electron transport layer 118, and electron injection layer 119 can be stacked sequentially from the anode side.

[0058] Note that the structure of the EL layer 100 is not limited to the structure shown in FIG1A, as long as it includes at least one selected from the hole injection layer 111, hole transport layer 112, electron transport layer 118, and electron injection layer 119. Alternatively, the EL layer 100 may also include a functional layer that can reduce the injection barrier of holes or electrons; a functional layer that can improve the transportability of holes or electrons; a functional layer that can hinder the transportability of holes or electrons; or a functional layer that can suppress quenching phenomena caused by electrodes. The functional layer can be a single layer or a stack of multiple layers.

[0059] <Light-emitting mechanism of light-emitting elements> The following explains the light-emitting mechanism of the light-emitting layer 130.

[0060] In a light-emitting element 150 according to one embodiment of the present invention, current flows through the EL layer 100 by applying a voltage between a pair of electrodes (electrode 101 and electrode 102) and injecting electrons and holes from the cathode and anode, respectively. Among the excitons generated by the recombination of carriers (electrons and holes), the statistical probability of the ratio of singlet excitons to triplet excitons (hereinafter referred to as the exciton generation probability) is 1:3. Therefore, the ratio of singlet excitons generated is 25%, and the ratio of triplet excitons generated is 75%. Therefore, it is important that triplet excitons contribute to light emission in order to improve the luminous efficiency of the light-emitting element. Thus, it is preferable to use a material capable of converting triplet excitation energy into light emission as the light-emitting layer 130.

[0061] As materials capable of converting triplet excitation energy into light emission, compounds that emit phosphorescence (hereinafter referred to as phosphorescent materials) can be cited as examples. In this specification, phosphorescent materials refer to compounds that emit phosphorescence but not fluorescence at any temperature within a temperature range above low temperature (e.g., 77 K) and below room temperature (i.e., above 77 K and below 313 K). Preferably, the phosphorescent material contains a metallic element with strong spin-orbit interaction; more specifically, it preferably contains a transition metal element, particularly preferably a platinum group element (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt)), and especially preferably iridium. Iridium is preferred because it increases the transition probability of the direct transition between the singlet ground state and the triplet excited state.

[0062] Furthermore, TADF materials are an example of materials capable of converting triple excitation energy into luminescence. TADF materials are defined as materials with a small difference between their S1 and T1 energy levels, capable of converting triple excitation energy into single excitation energy via antisystem crossing. Therefore, they can utilize minimal thermal energy to upconvert triple excitation energy into single excitation energy (antisystem crossing) and efficiently generate single excited states. Exciplexes, which are excited states formed by two substances, possess the TADF material function of converting triple excitation energy into single excitation energy due to the extremely small difference between their S1 and T1 energy levels.

[0063] As an indicator of the T1 energy level, the phosphorescence spectrum observed at low temperatures (e.g., 10 K) can be used. For TADF materials, preferably, a tangent is drawn at the tail end of the short-wavelength side of the fluorescence spectrum, and the energy of the wavelength of this extrapolated line is set as the S1 energy level; a tangent is drawn at the tail end of the short-wavelength side of the phosphorescence spectrum, and the energy of the wavelength of this extrapolated line is set as the T1 energy level, where the difference between S1 and T1 is less than 0.2 eV.

[0064] Furthermore, nanostructures of transition metal compounds with perovskite structures are examples of materials capable of converting triple excitation energy into luminescence. Metal halide perovskite nanostructures are particularly preferred. Nanoparticles and nanorods are preferred as such nanostructures.

[0065] Figure 1B is a schematic cross-sectional view of the light-emitting layer 130 of a light-emitting element according to one embodiment of the present invention. In one embodiment of the present invention, the light-emitting layer 130 comprises compound 131, compound 132, and compound 136. Compound 131 has the function of converting triple excitation energy into light emission, compound 132 has the function of converting single excitation energy into light emission, and compound 136 has the function of converting triple excitation energy into light emission. Because fluorescent materials have high stability, it is preferable to use a fluorescent material as compound 132 to obtain a light-emitting element with high reliability. Furthermore, because compound 131 has the function of converting triple excitation energy into light emission, it is preferable to generate carrier recombination in compound 131 in order to obtain a light-emitting element with high luminous efficiency. Therefore, preferably, both the single excitation energy and the triple excitation energy of the exciton generated by the recombination of carriers in compound 131 are ultimately transferred to the single excited state of compound 132 and the excited state of compound 136 (the triple excited state of the phosphorescent material and the single excited state of the TADF material), and compounds 132 and 136 emit light. Here, in the luminescent layer 130, compound 131 functions as an energy donor, while compounds 132 and 136 function as energy acceptors. In Figure 1C, the luminescent layer 130 is a fluorescent luminescent layer with compound 131 as the host material and compounds 132 and 136 as guest materials. That is, in Figure 1C, the host material is used as an energy donor, and the guest material is used as an energy acceptor. Furthermore, the luminescent layer 130 can obtain luminescence from compounds 132 and 136, which are guest materials.

[0066] <Example 1 of the structure of the light-emitting layer> Figure 1C illustrates an example of energy level correlation in the light-emitting layer of a light-emitting element according to one embodiment of the present invention. In this structural example, compound 131 is shown using a TADF material and compound 136 is shown using a phosphorescent material.

[0067] Additionally, Figure 1C shows the energy level correlations of compounds 131, 132, and 136 in the luminescent layer 130. The labels and symbols in Figure 1C are as follows. •Host(131): Compound 131 • Fluorecent Guest(132): Compound 132 • Phosphorecent Guest (136): Compound 136 •T C1: T1 energy level of compound 131 • S C1: S1 energy level of compound 131 • S FG: S1 energy level of compound 132 ·T FG: T1 energy level of compound 132 • TPG: T1 energy level of compound 136

[0068] Here, we focus on the triple excitation energy of compound 131 generated by current excitation. Compound 131 exhibits TADF characteristics. Therefore, compound 131 has the function of converting the triple excitation energy into a single excitation energy via upconversion (path A1 in Figure 1C). The single excitation energy of compound 131 can be rapidly transferred to compound 132 (path A2 in Figure 1C). In this case, it is preferable to satisfy SC1 ≥ SFG. Specifically, it is preferable to draw a tangent at the end of the short wavelength side of the fluorescence spectrum of compound 131, set the energy of the wavelength of this extrapolated line as SC1, and set the energy of the wavelength at the absorption end of the absorption spectrum of compound 132 as SFG, in which case SC1 ≥ SFG is satisfied. Furthermore, since compound 136 is a phosphorescent material, it can receive both the single and triple excitation energies of compound 131 (path A3 in Figure 1C). In this case, it is preferable that SC1 ≥ TC1 ≥ TPG. Furthermore, the energy of the wavelength at the absorption end of the absorption spectrum of compound 136 can be considered as TPG. Similarly, the energy of the wavelength at the short-wavelength side of the emission spectrum of compound 131 at low temperatures (e.g., 10 K) can be considered as TC1.

[0069] The triple excitation energy generated by compound 131 is transferred to the S1 energy level of compound 132, which is the guest material, via the aforementioned pathways A1 and A2. Compound 132 emits light, thereby converting the triple excitation energy into fluorescence, which improves the luminous efficiency of the light-emitting element. Furthermore, since compound 136 can also convert the triple excitation energy into light emission, multicolor emission can be efficiently obtained when compounds 132 and 136 exhibit different emission colors.

[0070] Here, in the luminescent layer 130, compounds 131, 132, and mixture 136 are mixed together. Therefore, it is possible for the triplet excitation energy of compound 131 to be converted to the triplet excitation energy of compound 132 (path A4 in Figure 1C) to compete with the aforementioned pathways A1, A2, and A3. Because compound 132 is a fluorescent material, its triplet excitation energy does not contribute to luminescence. That is, when energy transfer occurs via path A4, the luminous efficiency of the luminescent element decreases. Note that, in reality, as energy transfer path A4 from TC1 to TFG, there may be a path where the energy, once transferred to a triplet excited state higher than that of compound 132, is converted to TFG internally; however, this process is omitted in the diagram. The undesirable thermal deactivation process, i.e., the deactivation process to TFG, described later in this specification is the same.

[0071] Furthermore, as shown in Figure 1C, when SFG ≥ TPG, the process of converting the singlet excitation energy of compound 132 into fluorescence competes with the process of transferring it to TPG (path A5 in Figure 1C). That is, paths A3 and A5 exist as the process by which compound 136 receives excitation energy. Therefore, to obtain both the fluorescence of compound 132 and compound 136 in a good ratio, it is preferable that the concentration of compound 132 in the luminescent layer 130 is higher than the concentration of compound 136. Furthermore, it is preferable that the concentration of compound 136 in the luminescent layer 130 is lower, because carriers are less likely to recombine in compound 136.

[0072] Furthermore, sometimes there is competition between the process of converting the triple excitation energy of compound 136 into luminescence and the process of converting the triple excitation energy of compound 136 into the triple excitation energy of compound 132 (path A6 in Figure 1C). Because compound 132 is a fluorescent material, its triple excitation energy does not contribute to luminescence. That is, when energy transfer occurs via path A6, the luminous efficiency of the light-emitting element decreases.

[0073] Furthermore, the shorter the emission wavelength of the light emitted by the compound, the higher the energy at which the compound is excited. Therefore, to obtain good reliability of the light-emitting element, it is preferable to use a luminescent material with a high emission rate constant as the compound emitting light at a short wavelength, and preferably to use a fluorescent material. In other words, it is preferable that the light emitted by compound 132 has an emission peak on the shorter wavelength side compared to the light emitted by compound 136.

[0074] As intermolecular energy transfer mechanisms, the Foster mechanism (dipole-dipole interaction) and the Dexter mechanism (electron exchange interaction) are known. Because compound 132, acting as the energy acceptor, is a fluorescent material, the Dexter mechanism occurs significantly in energy transfer pathways A4 and A6. Generally, the Dexter mechanism occurs significantly when the distance between the energy donors (compounds 131 and 136) and the energy acceptor (compound 132) is less than 1 nm. Therefore, to suppress pathways A4 and A6, it is important to increase the distance between the energy donor and the energy acceptor.

[0075] Since the direct transition from the singlet ground state to the triplet excited state in compound 132 is a forbidden transition, the energy transfer from the singlet excited energy level (SC1) of compound 131 to the triplet excited energy level (TFG) of compound 132 is unlikely to be the main energy transfer process, and therefore is not illustrated.

[0076] In Figure 1C, the TFG levels mostly represent the energy levels of the luminescent elements derived from the fluorescent compounds. Therefore, more specifically, to suppress pathways A4 and A6, it is important to increase the distance between the energy donor and the luminescent element comprised of the fluorescent compound that receives the energy. A common method to increase this distance is to reduce the concentration of the fluorescent compound in the mixed film. However, when the concentration of the energy acceptor in the mixed film is reduced, in addition to the Dexter-based energy transfer from the energy donor to the fluorescent compound, the Foster-based energy transfer is also suppressed. In this case, because pathway A2 is based on the Foster mechanism, problems such as reduced luminous efficiency or decreased reliability of the luminescent element occur.

[0077] Therefore, the inventors of this case discovered that by using a fluorescent material having a protective base that extends the distance to the energy donor as an energy acceptor, the aforementioned decrease in luminescence efficiency can be suppressed. Furthermore, the inventors of this case also discovered that by using the aforementioned fluorescent material, both fluorescent and phosphorescent luminescence can be obtained from a luminescent layer containing a mixture of fluorescent and phosphorescent materials.

[0078] <The concept of fluorescent materials with protective bases> Figure 2A shows a schematic diagram of a fluorescent material without a protective base, which is a general fluorescent material, dispersed as a guest material in a host material. Figure 2B shows a schematic diagram of a fluorescent material with a protective base, used in a light-emitting element according to one embodiment of the present invention, dispersed as a guest material in a host material. The host material can be referred to as an energy donor and the guest material as an energy acceptor. Here, the protective base has the function of increasing the distance between the light emitter and the host material. In Figure 2A, the guest material 301 has a light emitter 310. The guest material 301 is used as an energy acceptor. On the other hand, in Figure 2B, the guest material 302 includes the light emitter 310 and the protective base 320. In Figures 2A and 2B, the guest material 301 and the guest material 302 are surrounded by the host material 330. In Figure 2A, because the distance between the luminescent element and the host material is relatively short, energy transfer from the host material 330 to the guest material 301 may involve energy transfer based on the Foster mechanism (path A7 in Figures 2A and 2B) and energy transfer based on the Dexter mechanism (path A8 in Figures 2A and 2B). When a triplet excitation energy transfer based on the Dexter mechanism occurs from the host material to the guest material, resulting in a triplet excited state of the guest material, non-radiative deactivation of the triplet excitation energy occurs if the guest material is a fluorescent material. This can be one of the reasons for the decrease in the luminous efficiency of the luminescent element.

[0079] On the other hand, in Figure 2B, the guest material 302 has a protective base 320. Therefore, the distance between the emitting element 310 and the host material 330 can be increased. Therefore, energy transfer based on the Dexter mechanism (path A8) can be suppressed. Therefore, by using a fluorescent material with a protective base, such as the guest material 302, in the emitting layer 130 shown in Figures 1A to 1C, paths A4 and A6 in Figure 1C can be suppressed.

[0080] Here, in order for the guest material 302 to emit light, since the Dexter mechanism is suppressed, the guest material 302 needs to receive energy from the host material 330 based on the Foster mechanism. That is, preferably, energy transfer based on the Foster mechanism is utilized efficiently while suppressing energy transfer based on the Dexter mechanism. It is known that energy transfer based on the Foster mechanism is also affected by the distance between the host material and the guest material. Generally speaking, when the distance between the host material 330 and the guest material 302 is less than 1 nm, the Dexter mechanism is dominant, and when it is more than 1 nm but less than 10 nm, the Foster mechanism is dominant. Generally speaking, when the distance between the host material 330 and the guest material 302 is more than 10 nm, energy transfer is not easy to occur. Here, the distance between the host material 330 and the guest material 302 can be referred to as the distance between the host material 330 and the emitting element 310.

[0081] Therefore, the protective base 320 preferably diffuses within a range of 1 nm to 10 nm from the light emitter 310. More preferably, it diffuses within a range of 1 nm to 5 nm from the light emitter 310. By employing this structure, energy transfer based on the Dexter mechanism from the host material 330 to the guest material 302 can be efficiently utilized while suppressing energy transfer based on the Foster mechanism. Therefore, a light-emitting element with high luminous efficiency can be manufactured.

[0082] Furthermore, to improve the energy transfer efficiency (increase the energy transfer rate) based on the Foster mechanism, it is preferable to increase the concentration of guest material 301 or guest material 302 relative to the host material 330. However, generally, when the concentration of the guest material increases, the energy transfer rate of the Foster mechanism also increases, which leads to a decrease in luminescence efficiency. Therefore, increasing the concentration of the guest material is difficult. There have been reports on luminescent elements in which the concentration of the guest material is as low as 1 wt% or less, using a material that has the function of converting triple excitation energy into luminescence as the host material.

[0083] On the other hand, in a light-emitting element according to one embodiment of the present invention, a fluorescent material having a protective base is used as the light-emitting layer. This allows for efficient utilization of the Foster mechanism while suppressing energy transfer based on the Dexter mechanism, thus increasing the concentration of the fluorescent material as the energy acceptor. As a result, a seemingly contradictory phenomenon can be achieved: simultaneously suppressing energy transfer based on the Dexter mechanism and increasing the energy transfer rate based on the Foster mechanism. The concentration of the fluorescent material relative to the host material is preferably 1 wt% or more and 30 wt% or less, more preferably 5 wt% or more and 20 wt% or less, and even more preferably 5 wt% or more and 15 wt% or less. By employing this structure, the energy transfer rate based on the Foster mechanism can be increased, thus obtaining a light-emitting element with high luminous efficiency. Furthermore, by using a material having the function of converting triple excitation energy into light emission as the host material, a fluorescent light-emitting element with high luminous efficiency comparable to that of a phosphorescent light-emitting element can be manufactured. In addition, because the luminous efficiency is improved by using a fluorescent material with high stability, a light-emitting element with high reliability can be manufactured. Furthermore, phosphorescent materials are also used in the light-emitting element of one embodiment of the present invention. Therefore, both fluorescence and phosphorescence can be obtained with high luminous efficiency.

[0084] Furthermore, in particular, the effect of the light-emitting element in one embodiment of the present invention is not merely an improvement in reliability due to the use of highly stable fluorescent materials. The aforementioned energy transfer often competes with the quenching process caused by deterioration or impurities. As the quenching rate constant of this quenching process increases over time, the luminescence ratio of the light-emitting element decreases. That is, the brightness of the light-emitting element deteriorates. However, as described above, in one embodiment of the present invention, the energy transfer rate based on the Foster mechanism can be higher than that of conventional light-emitting elements while suppressing energy transfer based on the Dexter mechanism. Therefore, the impact of competition with the quenching process can be reduced, and a longer lifespan of the element can be achieved.

[0085] Here, the luminescent body refers to the atomic group (skeleton) that causes luminescence in a fluorescent material. The luminescent body generally has π bonds, preferably contains an aromatic ring, and even more preferably has a fused aromatic ring or a fused heteroaromatic ring. Furthermore, as another embodiment, the luminescent body can be considered to be an atomic group (skeleton) containing an aromatic ring with a transition dipole vector existing on the ring plane.

[0086] Examples of fused aromatic or fused heteroaromatic rings include phenanthrene, stilbene, acridinone, phenanthrene, and phenanthrene-thiazolinone skeletons. In particular, fluorescent materials with naphthalene, anthracene, benzo[a]ene, benzo[b]ene, triphenylene, fused tetraphenylene, pyrene, perylene, coumarin, quinacridone, and naphthobisbenzofuran skeletons are preferred due to their high fluorescence quantum yield.

[0087] The protecting group needs to have a triplet excitation level higher than the T1 level of both the luminescent material and the host material. Therefore, saturated hydrocarbon groups are preferred. This is because substituents without π bonds have a high triplet excitation level. Furthermore, substituents without π bonds do not have the function of transporting carriers (electrons or holes). Therefore, saturated hydrocarbon groups can result in a long distance between the luminescent material and the host material with almost no impact on the excited state or carrier transportability. In addition, in organic compounds containing both substituents without π bonds and substituents with π conjugation, in many cases, the leading orbitals {HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital)} exist on the side of the substituent with π conjugation, especially in cases where the luminescent material has leading orbitals. As explained later, for energy transfer based on the Dexter mechanism, the overlap of the HOMOs of the energy donor and the energy acceptor, as well as the overlap of the LUMOs of the energy donor and the energy acceptor, are important. Therefore, by using saturated hydrocarbon groups as protecting groups, the distance between the leading orbital domain of the host material as an energy donor and the leading orbital domain of the guest material as an energy acceptor can be increased, thus suppressing energy transfer based on the Dexter mechanism.

[0088] Specific examples of protecting groups include alkyl groups with 1 to 10 carbon atoms. Because a long distance between the luminescent material and the host material is required, a large substituent is preferred for the protecting group. Therefore, alkyl groups with 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl groups with 3 to 10 carbon atoms, and trialkylsilyl groups with 3 to 10 carbon atoms are suitable. In particular, a large branched alkyl group is preferred. Furthermore, a large substituent containing a quaternary carbon is particularly preferred.

[0089] Furthermore, it is preferable to have five or more protecting groups relative to a single luminescent body. By employing this structure, the entire luminescent body can be covered by the protecting groups, thus allowing for appropriate adjustment of the distance between the host material and the luminescent body. Although Figure 2B shows the case where the luminescent body and the protecting groups are directly bonded, it is more preferable that the protecting groups and the luminescent body are not directly bonded. For example, the protecting groups can also be bonded to the luminescent body via divalent or higher substituents such as aryl or amino groups. By using these substituents to bond the protecting groups to the luminescent body, the distance between the luminescent body and the host material can be effectively increased. Therefore, when the luminescent body and the protecting groups are not directly bonded, having four or more protecting groups relative to a single luminescent body can effectively suppress energy transfer based on the Dexter mechanism.

[0090] Furthermore, the divalent or higher substituents that bond the luminescent material and the protecting group are preferably substituents with π-conjugation. By employing this structure, the luminescence color, HOMO energy level, glass transition point, and other physical properties of the guest material can be tuned. Additionally, the protecting group is preferably positioned on the outermost side when the molecular structure is observed with the luminescent material at the center.

[0091] <Examples of fluorescent materials with protective groups and their molecular structures> Here, the structure of a fluorescent material N,N'-[(2-tert-butylanthracene)-9,10-diyl]-N,N'-bis(3,5-di-tert-butylphenyl)amine (abbreviated as: 2tBu-mmtBuDPhA2Anth), which can be used in a light-emitting element according to one embodiment of the present invention, represented by the following structural formula (102), is shown. In 2tBu-mmtBuDPhA2Anth, the anthracene ring is the light emitter, and the tert-butyl(tBu) group is used as a protecting group.

[0092] [Chemical Formula 1]

[0093] In Figure 3B, the above-mentioned 2tBu-mmtBuDPhA2Anth is represented by a ball-and-stick model. Figure 3B shows the view of 2tBu-mmtBuDPhA2Anth from the direction of the arrow in Figure 3A (horizontally to the anthracene ring surface). The shaded area in Figure 3B represents the upper part of the anthracene ring surface, which serves as the luminescent element. It can be confirmed that this upper part has a region overlapping with the tBu group, which serves as the protecting group. For example, in Figure 3B, the atom indicated by arrow (a) is the carbon atom of the tBu group that overlaps with the shaded area, and the atom indicated by arrow (b) is the hydrogen atom of the tBu group that overlaps with the shaded area. That is, in 2tBu-mmtBuDPhA2Anth, the atom constituting the protecting group is located directly on one side of the luminescent element surface, and the atom constituting the protecting group is also located directly on the other side of the luminescent element surface. By employing this structure, even when the guest material is dispersed in the host material, the distance between the anthracene ring and the host material can be increased in both the planar and vertical directions of the anthracene ring, which acts as the luminescent body, thus suppressing energy transfer based on the Dexter mechanism.

[0094] For example, in cases where the energy transfer involves a migration between HOMO and LUMO, the overlap of the HOMO of the host material and the HOMO of the guest material, as well as the overlap of the LUMO of the host material and the LUMO of the guest material, is crucial for energy transfer based on the Dexter mechanism. The Dexter mechanism occurs significantly when the HOMO and LUMO of these two materials overlap. Therefore, to suppress the Dexter mechanism, it is important to suppress the overlap of the HOMO and LUMO of the two materials. That is, it is important to maintain a long distance between the framework and the host material, which are related to the excited state. Here, in fluorescent materials, HOMO and LUMO often have luminescent properties. For example, when the HOMO and LUMO of the guest material diffuse above and below the luminescent surface (above and below the anthracene ring in 2tBu-mmtBuDPhA2Anth), it is important in the molecular structure for the protecting group to cover the area above and below the luminescent surface.

[0095] Furthermore, in fused aromatic rings or fused heteroaromatic rings such as pyrene rings or anthracene rings used as luminescent elements, a transition dipole vector exists on the ring plane. Therefore, in Figure 3B, 2tBu-mmtBuDPhA2Anth preferably has a region overlapping with the tBu group as a protecting group on the plane where the transition dipole vector exists, that is, on the face of the anthracene ring. Specifically, at least one of the atoms constituting the plurality of protecting groups (tBu groups in Figures 3A and 3B) is located on one face of the fused aromatic ring or fused heteroaromatic ring (anthracene ring in Figures 3A and 3B), and at least one of the atoms constituting the plurality of protecting groups is located on the other face of the fused aromatic ring or fused heteroaromatic ring. By adopting this structure, even when the guest material is dispersed in the host material, the distance between the luminescent element and the host material can be long, thus suppressing energy transfer based on the Dexter mechanism. Furthermore, it is preferable to configure the protecting group such as the tBu group in a manner that covers the luminescent element such as the anthracene ring.

[0096] <Structural Example 2 of the Light-Emitting Layer> Figure 4C illustrates an example of energy level correlation in the light-emitting layer 130 of a light-emitting element 150 according to one embodiment of the present invention. The light-emitting layer 130 shown in Figure 4A includes compounds 131, 132, 136, and 133. In one embodiment of the present invention, compound 132 is preferably a fluorescent material, and compound 136 is preferably a phosphorescent material. Furthermore, in this structural example, compounds 131 and 133 are a combination forming an excited-state complex.

[0097] The combination of compounds 131 and 133 can be any combination capable of forming an excited-state complex. Preferably, one of them is a compound with hole-transferring capabilities (hole transport) and the other is a compound with electron-transferring capabilities (electron transport). In this case, donor-acceptor type excited-state complexes are easily formed, and excited-state complexes can be formed efficiently. Furthermore, when the combination of compounds 131 and 133 is a combination of a hole-transferring compound and an electron-transferring compound, the carrier balance can be easily controlled by adjusting their mixing ratio. Specifically, the ratio of the hole-transferring compound to the electron-transferring compound is preferably in the range of 1:9 to 9:1 (weight ratio). Moreover, with this structure, the carrier balance can be easily controlled, thereby allowing for easy control of the carrier recombination region.

[0098] Furthermore, as a combination of host materials for efficiently forming excited-state complexes, it is preferable that the HOMO level of one of compounds 131 and 133 is higher than that of the other, and that the LUMO level of one of them is higher than that of the other. Alternatively, the HOMO level of compound 131 may be equal to that of compound 133, or the LUMO level of compound 131 may be equal to that of compound 133.

[0099] Note that the LUMO and HOMO energy levels of a compound can be determined from the compound's electrochemical properties (reduction potential and oxidation potential) measured by cyclic voltammetry (CV).

[0100] For example, when compound 131 exhibits hole transport and compound 133 exhibits electron transport, as shown in the band diagram of Figure 4B, it is preferable that the HOMO level of compound 131 is higher than that of compound 133, and that the LUMO level of compound 131 is higher than that of compound 133. Due to this energy level correlation, holes and electrons acting as carriers, injected from a pair of electrodes (electrode 101 and electrode 102), are readily injected into compound 131 and compound 133, respectively, which is therefore preferable.

[0101] Additionally, in Figure 4B, Comp(131) represents compound 131, Comp(133) represents compound 133, ΔEC1 represents the energy difference between the LUMO and HOMO levels of compound 131, ΔEC3 represents the energy difference between the LUMO and HOMO levels of compound 132, and ΔEE represents the energy difference between the LUMO level of compound 133 and the HOMO level of compound 131.

[0102] Furthermore, the excited-state complex formed from compounds 131 and 133 possesses HOMO molecular orbitals in compound 131 and LUMO molecular orbitals in compound 133. Additionally, the excitation energy of this excited-state complex is approximately equivalent to the energy difference (ΔEC1) between the LUMO energy level of compound 133 and the HOMO energy level of compound 131, and is less than the energy difference (ΔEC3) between the LUMO and HOMO energy levels of compound 131. Therefore, by forming an excited-state complex from compounds 131 and 133, an excited state can be formed with a lower excitation energy. Furthermore, this excited-state complex, due to its lower excitation energy, is capable of forming a stable excited state.

[0103] Figure 4C shows the energy level correlations of compounds 131, 132, and 133 in the luminescent layer 130. The labels and symbols in Figure 4C are shown below. ·Comp(131): Compound 131 ·Comp(133): Compound 133 • Fluorescent Guest(132): Compound 132 • S C1: S1 energy level of compound 131 •T C1: T1 energy level of compound 131 • S C3: S1 energy level of compound 133 •T C3: T1 energy level of compound 133 • S FG: S1 energy level of compound 132 ·T FG: T1 energy level of compound 132 • SE: S1 energy level of excited-state complexes ·TE: T1 energy level of excited-state complexes

[0104] In a light-emitting element according to one embodiment of the present invention, compounds 131 and 133 contained in the light-emitting layer 130 form an excited-state complex. The S1 energy level (SE) of the excited-state complex and the T1 energy level (TE) of the excited-state complex are adjacent energy levels (refer to path A9 in Figure 4C).

[0105] The excitation energy levels (SE and TE) of the excited-state complex are lower than the S1 energy levels (SC1 and SC3) of the substances forming the excited-state complex (compound 131 and compound 133), so the excited state can be formed at a lower excitation energy. As a result, the driving voltage of the light-emitting element 150 can be reduced.

[0106] Because the S1 level (SE) and T1 level (TE) of the excited-state complex are adjacent, it readily exhibits antisystem crossing and thus TADF characteristics. Therefore, the excited-state complex has the ability to convert triple excitation energy into single excitation energy via upconversion (path A 10 in Figure 4C). The single excitation energy of the excited-state complex can be rapidly transferred to compound 132 (path A 11 in Figure 4C). Preferably, SE ≥ SFG. In path A 11, the excited-state complex acts as an energy donor, and compound 132 acts as an energy acceptor. Specifically, it is preferable to draw a tangent at the short-wavelength side of the fluorescence spectrum of the excited-state complex, setting the energy of the wavelength of this extrapolated line as SE, and setting the energy of the wavelength at the absorption end of the absorption spectrum of compound 132 as SFG, thus satisfying SE ≥ SFG. Furthermore, since compound 136 is a phosphorescent material, it can receive both the singlet and triplet excitation energies of the excited-state complex (path A12 in Figure 4C). That is, energy transfer from SE and TE to TPG is possible. Preferably, SE ≥ TPG and TE ≥ TPG. Moreover, when SFG ≥ TPG, the process of converting the singlet excitation energy of compound 132 into fluorescence competes with the process of transferring it to TPG (path A5 in Figure 4C). Compound 136 can receive excitation energy via paths A12 and A5. Therefore, the emission of both compound 132 and compound 136 can be obtained from the luminescent layer 130.

[0107] Additionally, although not illustrated, energy transfer from compounds 131 and 133 to compounds 132 and / or 136 can also occur.

[0108] To enhance TADF properties, it is preferable that the T1 energy levels of compounds 131 and 133, i.e., TC1 and TC3, are above TE. As an indicator, it is preferable that the emission peak wavelengths on the shortest wavelength side of the phosphorescence spectra of compounds 131 and 133 are both below the maximum emission peak wavelength of the excited-state complex. Alternatively, it is preferable to draw a tangent at the end of the short-wavelength side of the fluorescence spectrum of the excited-state complex, set the energy of the wavelength of this extrapolated line to SE, and draw tangents at the end of the short-wavelength side of the phosphorescence spectra of compounds 131 and 133 respectively, setting the energy of the wavelength of this extrapolated line to TC1 and TC3 of each compound, where SE ET C1 ≤ 0.2 eV and SE ET C3 ≤ 0.2 eV.

[0109] The triple excitation energy occurring in the luminescent layer 130, via the aforementioned path A9 and the energy transfer from the S1 energy level of the excited-state complex to the S1 energy level of compound 132 (path A11), enables compound 132 to emit light. Therefore, by using the material that forms the excited-state complex in the luminescent layer 130, the luminous efficiency of the luminescent element can be improved.

[0110] In one embodiment of the present invention, a fluorescent material with a protective group is used as the light emitter in a light-emitting element of compound 132. By employing this structure, as described above, energy transfer based on the Dexter mechanism represented by paths A13 and A6 can be suppressed, and deactivation at the triple excitation energy can be suppressed. Therefore, a light-emitting element with high luminous efficiency can be obtained.

[0111] In this specification and other materials, the process described above through paths A9 to A11 is sometimes referred to as ExSET (Exciplex-Singlelet Energy Transfer) or ExEF (Exciplex-Enhanced Fluorescence). In other words, in the luminescent layer 130, an excitation energy supply is generated from the excited-state complex to the fluorescent material.

[0112] <Structural Example 3 of the Light-Emitting Layer> In this structural example, we will describe the case where a phosphorescent material is used as the light-emitting element of compound 133 utilizing the above-described ExEF. That is, we will describe the case where a phosphorescent material is used in one of the compounds that form an excited-state complex.

[0113] In this structural example, a compound containing heavy atoms is used as one of the compounds forming an excited-state complex. Therefore, the intersystem transition between the singlet excited state and the triplet excited state is facilitated. Thus, an excited-state complex capable of transitioning from the triplet excited state to the singlet ground state (i.e., capable of phosphorescence) can be formed. In this case, unlike a typical excited-state complex, the triplet excitation energy level (TE) of the excited-state complex is the energy level of the energy donor; therefore, TE is preferably higher than or equal to the singlet excitation energy level (S FG) of compound 132, which is used as the luminescent material. Specifically, it is preferable to draw a tangent at the tail of the emission spectrum of the excited-state complex using heavy atoms on the shorter wavelength side, set the energy of the wavelength of this extrapolated line as TE, and set the energy of the wavelength at the absorption end of the absorption spectrum of compound 132 as S FG, where TE ≥ S FG.

[0114] In this energy level-dependent case, the triple excitation energy of the generated excited-state complex can be transferred from the triple excitation energy level (TE) of the excited-state complex to the single excitation energy level (SFG) of compound 132. Note that the S1 energy level (SE) and T1 energy level (TE) of the excited-state complex are adjacent to each other, which sometimes makes it difficult to clearly distinguish between fluorescence and phosphorescence in the emission spectrum. In this case, fluorescence and phosphorescence can sometimes be distinguished based on the emission lifetime.

[0115] The phosphorescent material used in the above structure preferably contains heavy atoms such as Ir, Pt, Os, Ru, and Pd. On the other hand, in this structural example, compound 133 of the phosphorescent material is also used as an energy donor, thus its quantum yield can be either high or low. That is, the energy transfer from the triplet excitation level of the excited-state complex to the singlet excitation level of the fluorescent material can be an allowed transition. In the energy transfer from the excited-state complex composed of the above-mentioned phosphorescent material or from the above-mentioned phosphorescent material to the fluorescent material, the energy transfer from the triplet excitation level of the energy donor to the singlet excitation level of the guest material (energy acceptor) is an allowed transition, and therefore preferred. Therefore, the triplet excitation energy of the excited-state complex can be transferred to the S1 level (S FG) of the guest material via path A11 without going through path A10 in Figure 4C. That is, the triplet excitation energy and the singlet excitation energy can be transferred to the S1 level of the guest material only through paths A9 and A11. In pathway A 11, the excited-state complex is used as an energy donor, and compound 132 and / or compound 136 is used as an energy acceptor.

[0116] In one embodiment of the present invention, a fluorescent material with a protective group is used as the light emitter in a light-emitting element of compound 132. By employing this structure, as described above, energy transfer based on the Dexter mechanism represented by paths A13 and A6 can be suppressed, and deactivation at the triple excitation energy can be suppressed. Therefore, a light-emitting element with high luminous efficiency can be obtained.

[0117] <Example 4 of the structure of the light-emitting layer> In this structural example, FIG4D illustrates the case where compound 133, as a light-emitting element utilizing the above-described ExEF, uses a material with TADF properties.

[0118] Since compound 133 is a TADF material, it does not form an excited-state complex and thus has the ability to convert the triplet excitation energy into a singlet excitation energy via upconversion (path A 14 in Figure 4D). The singlet excitation energy of compound 133 can be rapidly transferred to compound 132 (path A 15 in Figure 4D). In this case, it is preferable that SC3 ≥ SFG.

[0119] Similar to the above-described example of a light-emitting layer structure, in one embodiment of the light-emitting element of the present invention, there are paths through which the triple excitation energy is transferred to compound 132, which serves as a fluorescent material, via paths A9 to A11 in FIG. 4D, and paths through paths A14 and A15 in FIG. 4D. Because there are multiple paths through which the triple excitation energy is transferred to the fluorescent material, the luminous efficiency can be further improved.

[0120] Additionally, although not illustrated, energy transfer can also occur from compound 131 to compound 132 and / or compound 136. Furthermore, energy transfer can also occur from compound 133 to compound 136.

[0121] <Example 5 of the structure of the light-emitting layer> Figure 5B illustrates an example of energy level correlation in the light-emitting layer 130 of a light-emitting element 150 according to one embodiment of the present invention. The light-emitting layer 130 in Figure 5A includes compounds 131, 132, 136, and 133. In one embodiment of the present invention, compound 132 is a fluorescent material with a protecting group, and compound 136 is a phosphorescent material. Compound 133 has the function of converting triple excitation energy into light emission. In this structural example, the description assumes that compound 133 is a phosphorescent material. The reference numerals and symbols in Figure 5B are the same as those shown in Figure 4C.

[0122] In one embodiment of the light-emitting element of the present invention, singletons and tripletons are generated because carrier recombination mainly occurs in compound 131 contained in the light-emitting layer 130. Since compound 133 is a phosphorescent material, by selecting a material that satisfies the relationship TC3 ≤ TC1, the singleton and tripleton excitation energies generated in compound 131 can be transferred to the TC3 energy level of compound 133 (path A 16 in FIG. 5B). Note that some carriers may recombine in compound 133.

[0123] The phosphorescent material used in the above structure preferably contains heavy atoms such as Ir, Pt, Os, Ru, and Pd. On the other hand, as described above, in this structural example, compound 133 of the phosphorescent material is also used as an energy donor, thus its quantum yield can be either high or low. When the phosphorescent material is compound 133, the energy transfer from the triplet excitation level of the energy donor to the singlet excitation level of the guest material (energy acceptor) is an allowed transition, which is preferred. Therefore, the triplet excitation energy of compound 133 can be transferred to the S1 level (S FG) of the guest material via path A 17. In path A 17, compound 133 is used as the energy donor, and compound 132 is used as the energy acceptor. At this time, with T C3 ≥ S FG satisfied, the excitation energy of compound 133 is efficiently transferred to the singlet excited state of compound 132, which is also preferred. Specifically, preferably, a tangent line is drawn at the end of the short-wavelength side of the phosphorescence spectrum of compound 133, and the energy of the wavelength of this extrapolated line is set to TC3. The energy of the wavelength at the absorption end of the absorption spectrum of compound 132 is set to SFG, where TC3 ≥ SFG. Furthermore, since compound 136 is a phosphorescent material, it can receive the triple excitation energy of compound 133 (path A 18 in Figure 5B). That is, energy transfer from TC3 to TPG is possible. In this case, preferably TC3 ≥ TPG. Moreover, when SFG ≥ TPG, the process of converting the single excitation energy of compound 132 into fluorescence competes with the process of transferring it to TPG (path A 5 in Figure 5B). Compound 136 can receive excitation energy through paths A 18 and A 5. Therefore, the emission of both compound 132 and compound 136 can be obtained from the luminescent layer 130.

[0124] Additionally, although not illustrated, energy transfer from compound 131 to compound 132 and / or compound 136 can also occur.

[0125] In one embodiment of the present invention, the light-emitting element uses a guest material with a protective group as its light-emitting body in compound 132. By employing this structure, as described above, energy transfer based on the Dexter mechanism represented by paths A19 and A6 can be suppressed, and deactivation at the triple excitation energy can be suppressed. Therefore, a fluorescent light-emitting element with high luminous efficiency can be obtained.

[0126] <Structure Example of a Light-Emitting Layer 6> Figure 5C illustrates an example of energy level correlation in the light-emitting layer 130 of a light-emitting element 150 according to one embodiment of the present invention. The light-emitting layer 130 in Figure 5C includes compounds 131, 132, 136, and 133. In one embodiment of the present invention, compound 132 is a fluorescent material with a protecting group, and compound 136 is a phosphorescent material. Compound 133 has the function of converting triple excitation energy into light emission. In this structural example, the description assumes that compound 133 is a compound with TADF properties. The reference numerals and symbols in Figure 5C are the same as those shown in Figure 4C.

[0127] In a light-emitting element according to one embodiment of the present invention, singletons and triplet excitons are generated because carrier recombination mainly occurs in compound 131 contained in the light-emitting layer 130. By selecting materials that satisfy the relationships SC3≤SC1 and TC3≤TC1, the singleton and triplet excitation energies generated in compound 131 can be transferred to the SC3 and TC3 energy levels of compound 133 (path A 20 in FIG. 5C). Note that some carriers may recombine in compound 133.

[0128] Here, since compound 133 is a TADF material, it has the function of converting triple excitation energy into single excitation energy via upconversion (path A 21 in Figure 5C). The single excitation energy of compound 133 can be rapidly transferred to compound 132 (path A 22 in Figure 5C). Preferably, SC3 ≥ SFG is satisfied. Specifically, it is preferable to draw a tangent at the end of the short-wavelength side of the fluorescence spectrum of compound 133, setting the energy of the wavelength of this extrapolated line to SC3, and setting the energy of the wavelength at the absorption end of the absorption spectrum of compound 132 to SFG, thus satisfying SC3 ≥ SFG. Through the process from path A 20 to path A 22, the triple excitation energy in the luminescent layer 130 can be converted into the fluorescence emission of compound 132. In path A 22, compound 133 is used as an energy donor, and compound 132 is used as an energy acceptor. Furthermore, since compound 136 is a phosphorescent material, it can receive both the singlet and triplet excitation energies of compound 133 (path A 23 in Figure 5C). That is, energy transfer from SC3 and TC3 to TPG is possible. Moreover, when SFG ≥ TPG, the process of converting the singlet excitation energy of compound 132 into fluorescence competes with the process of transferring it to TPG (path A 5 in Figure 5C). Compound 136 can receive excitation energy via paths A 23 and A 5. Therefore, the emission of both compounds 132 and 136 can be obtained from the luminescent layer 130.

[0129] Additionally, although not illustrated, energy transfer from compound 131 to compound 132 and / or compound 136 can also occur.

[0130] In one embodiment of the present invention, the light-emitting element uses a guest material with a protective group as its light-emitting body in compound 132. By employing this structure, as described above, energy transfer based on the Dexter mechanism represented by paths A24 and A6 can be suppressed, and deactivation at the triple excitation energy can be suppressed. Therefore, a fluorescent light-emitting element with high luminous efficiency can be obtained.

[0131] <Energy Transfer Mechanism> The Foster and Dexter mechanisms will now be explained. While this explanation focuses on the energy transfer process between the molecules of the first and second materials, involving the supply of excitation energy from the first material in the excited state to the second material in the ground state, the same applies when either of these is an excited-state complex.

[0132] <<Foster Mechanism>> In the Foster mechanism, direct intermolecular contact is not required for energy transfer; energy transfer occurs through the resonance phenomenon of dipole oscillations between the first and second materials. Through this resonance phenomenon, the first material supplies energy to the second material, the excited state of the first material becomes the ground state, and the ground state of the second material becomes the excited state. Furthermore, equation (1) shows the rate constant kh* → g in the Foster mechanism.

[0133] [Formula 1]

[0134] In formula (1), ν represents the oscillation number, f'h(ν) represents the normalized emission spectrum of the first material (fluorescence spectrum when discussing energy transfer from a singlet excited state, and phosphorescence spectrum when discussing energy transfer from a triplet excited state), εg(ν) represents the molar absorptivity of the second material, N represents the Avogadro number, n represents the refractive index of the medium, R represents the intermolecular distance between the first and second materials, τ represents the lifetime of the measured excited state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, Φ represents the luminescence quantum yield (fluorescence quantum yield when discussing energy transfer from a singlet excited state, and phosphorescence quantum yield when discussing energy transfer from a triplet excited state), and K2 represents the alignment coefficient (0 to 4) of the transition dipole moments of the first and second materials. Furthermore, in random alignment, K2 = 2 / 3.

[0135] <<Dexter Mechanism>> In the Dexter mechanism, the first and second materials approach the effective contact distance of overlapping production orbitals, and energy transfer occurs by exchanging electrons in the excited state of the first material and the ground state of the second material. Furthermore, equation (2) shows the rate constant kh* → g in the Dexter mechanism.

[0136] [Formula 2]

[0137] In formula (2), h represents Planck's constant, K represents a constant with energy dimension, ν represents the oscillation number, f'h(ν) represents the normalized emission spectrum of the first material (fluorescence spectrum when discussing energy transfer from a singlet excited state, and phosphorescence spectrum when discussing energy transfer from a triplet excited state), ε'g(ν) represents the normalized absorption spectrum of the second material, L represents the effective molecular radius, and R represents the intermolecular distance between the first and second materials.

[0138] Here, the energy transfer efficiency ΦET from the first material to the second material is expressed by formula (3). kr represents the rate constant of the luminescence process of the first material (fluorescence when discussing energy transfer from a singlet excited state, and phosphorescence when discussing energy transfer from a triplet excited state), kn represents the rate constant of the non-luminescence process (thermal deactivation or intersystem crossing) of the second material, and τ represents the lifetime of the excited state of the first material as measured.

[0139] [Formula 3]

[0140] As can be seen from formula (3), in order to improve the energy transfer efficiency ΦET, the energy transfer rate constant kh* → g can be increased to make the other competing rate constants kr+kn (=1 / τ) relatively smaller.

[0141] <<Concepts for Enhancing Energy Transfer>> First, consider energy transfer based on the Foster mechanism. By substituting equation (1) into equation (3), τ can be eliminated. Therefore, in the Foster mechanism, the energy transfer efficiency ΦET does not depend on the lifetime τ of the excited state of the first material. Furthermore, when the luminescence quantum yield Φ is high, it can be said that the energy transfer efficiency ΦET is high.

[0142] Furthermore, the overlap between the emission spectrum of the first material and the absorption spectrum of the second material (corresponding to absorption during the migration from the singlet ground state to the singlet excited state) is preferably large. Moreover, the moiré absorptivity of the second material is preferably high. This means that the emission spectrum of the first material overlaps with the absorption band appearing on the longest wavelength side of the second material. Note that since direct transitions from the singlet ground state to the triplet excited state are forbidden in the second material, the moiré absorptivity in the triplet excited state is negligible. Therefore, the energy transfer process from the excited state of the first material to the triplet excited state of the second material based on the Foster mechanism can be ignored; only the energy transfer process to the singlet excited state of the second material needs to be considered.

[0143] Furthermore, according to formula (1), the energy transfer rate based on the Foster mechanism is inversely proportional to the sixth power of the intermolecular distance R between the first and second materials. As mentioned above, when R is less than 1 nm, the energy transfer based on the Dexter mechanism is dominant. Therefore, in order to increase the energy transfer rate based on the Foster mechanism while suppressing the energy transfer based on the Dexter mechanism, the intermolecular distance is preferably 1 nm or more and 10 nm or less. Therefore, the protecting group is required to be not too large, and the number of carbon atoms constituting the protecting group is preferably 3 or more and 10 or less.

[0144] Next, consider energy transfer based on the Dexter mechanism. From equation (2), it can be seen that to increase the rate constant kh* → g, the overlap between the emission spectrum of the first material (fluorescence when discussing energy transfer from a singlet excited state, and phosphorescence when discussing energy transfer from a triplet excited state) and the absorption spectrum of the second material (equivalent to absorption during the migration from the singlet ground state to the singlet excited state) should ideally be large. Therefore, by overlapping the emission spectrum of the first material with the absorption band present on the longest wavelength side of the second material, the energy transfer efficiency can be optimized.

[0145] Furthermore, when formula (2) is substituted into formula (3), it can be seen that the energy transfer efficiency ΦET in the Dexter mechanism depends on τ. Because the Dexter mechanism is an energy transfer process based on electron exchange, similar to the energy transfer from the singlet excited state of the first material to the singlet excited state of the second material, it also produces the energy transfer from the triplet excited state of the first material to the triplet excited state of the second material.

[0146] In one embodiment of the light-emitting element of the present invention, the second material is a fluorescent material, so the energy transfer efficiency to the triplet excited state of the second material is preferably low. That is, the energy transfer efficiency from the first material to the second material based on the Dexter mechanism is preferably low, while the energy transfer efficiency from the first material to the second material based on the Foster mechanism is preferably high.

[0147] As mentioned above, the energy transfer efficiency based on the Foster mechanism does not depend on the lifetime τ of the excited state of the first material. On the other hand, the energy transfer efficiency based on the Dexter mechanism depends on the excitation lifetime τ of the first material. In order to reduce the energy transfer efficiency based on the Dexter mechanism, the excitation lifetime τ of the first material is preferably short.

[0148] Therefore, in one embodiment of the present invention, an excited-state complex, a phosphorescent material, or a TADF material is used as the first material. These materials have the function of converting triplet excitation energy into luminescence. The energy transfer efficiency of the Foster mechanism depends on the luminescence quantum yield of the energy donor; therefore, the first material, such as a phosphorescent material, an excited-state complex, or a TADF material, which can convert the energy of the triplet excited state into luminescence, can utilize the Foster mechanism to transfer its excitation energy to the second material. On the other hand, with the structure of one embodiment of the present invention, antisystem crossing from the triplet excited state to the singlet excited state of the first material (excited-state complex or TADF material) can be promoted, and the excitation lifetime τ of the triplet excited state of the first material can be shortened. In addition, the transition from the triplet excited state to the singlet ground state of the first material (phosphorescent material or excited-state complex using phosphorescent material) can be promoted, and the excitation lifetime τ of the triplet excited state of the first material can be shortened. As a result, the energy transfer efficiency based on the Dexter mechanism from the triplet excited state of the first material to the triplet excited state of the fluorescent material (second material) can be reduced.

[0149] In a light-emitting element according to one embodiment of the present invention, as described above, a fluorescent material with a protective group is used as the second material. Therefore, the intermolecular distance between the first material and the second material can be large. Thus, in a light-emitting element according to one embodiment of the present invention, by using a material having the function of converting triple excitation energy into light emission in the first material and using a fluorescent material with a protective group in the second material, the energy transfer efficiency based on the Dexter mechanism can be reduced. As a result, non-radiative deactivation of the triple excitation energy in the light-emitting layer 130 can be suppressed, thereby providing a light-emitting element with high luminous efficiency.

[0150] <Materials> Next, the components of a light-emitting element according to an embodiment of the present invention will be described.

[0151] <<Emitting Layer>> The materials that can be used in the light-emitting layer 130 will be described below. In the light-emitting layer of the light-emitting element according to one embodiment of the present invention, an energy acceptor having the function of converting triple excitation energy into light emission and an energy donor having a protective base are used. As materials having the function of converting triple excitation energy into light emission, TADF characteristic materials and phosphorescent materials can be cited.

[0152] Examples of luminescent compounds, such as those with phenanthrene, stilbene, acridinone, phenanthrene, and phenanthrene-thiazolinone skeletons, that serve as energy acceptors include those with phenanthrene, stilbene, acridinone, naphthalene, anthracene, naphthalene, pyrene, perylene, coumarin, quinacridone, and naphthobisbenzofuran skeletons, exhibit high fluorescence quantum yields and are therefore preferred.

[0153] Furthermore, as a protecting group, it is preferred to be an alkyl group with 1 or more and 10 or less carbon atoms, a cycloalkyl group with 3 or more and 10 or less carbon atoms, a branched alkyl group with 3 or more and 10 or less carbon atoms, or a trialkylsilyl group with 3 or more and 12 or less carbon atoms.

[0154] Examples of alkyl groups having 1 or more but less than 10 carbon atoms include methyl, ethyl, propyl, pentyl, and hexyl, with branched alkyl groups having 3 or more but less than 10 carbon atoms (described later) being particularly preferred. Note that the alkyl group is not limited to these.

[0155] Examples of cycloalkyl groups having 3 or more but less than 10 carbon atoms include cyclopropyl, cyclobutyl, cyclohexyl, norbornel, and adamantyl. The cycloalkyl group is not limited to these. Furthermore, when the cycloalkyl group has a substituent, examples of substituents include alkyl groups having 1 to 7 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, dibutyl, tributyl, pentyl, and hexyl; cycloalkyl groups having 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, cycloheptyl, and 8,9,10-trinorbornel; and aryl groups having 6 to 12 carbon atoms such as phenyl, naphthyl, and biphenyl.

[0156] Examples of branched alkyl groups with 3 or more but less than 10 carbon atoms include isopropyl, dibutyl, isobutyl, tributyl, isopentyl, dipentyl, tripentyl, neopentyl, isohexyl, 3-methylpentyl, 2-methylpentyl, 2-ethylbutyl, 1,2-dimethylbutyl, and 2,3-dimethylbutyl. However, the branched alkyl group is not limited to these examples.

[0157] Examples of trialkylsilyl groups with 3 or more but less than 12 carbon atoms include trimethylsilyl, triethylsilyl, and tributyldimethylsilyl. However, the trialkylsilyl group is not limited to these examples.

[0158] Furthermore, the preferred molecular structure of the energy acceptor is one in which the luminescent material is bonded to two or more diarylamine groups, and each of the aryl groups has at least one protecting group. More preferably, at least two protecting groups are bonded to each aryl group. This is because the more protecting groups present, the greater the effect of suppressing energy transfer based on the Dexter mechanism when the guest material is used in the luminescent layer. To suppress the increase in molecular weight and maintain sublimation, the diarylamine group is preferably a diphenylamine group.

[0159] By bonding two or more diarylamine groups to a light emitter, fluorescent materials with high quantum yields can be obtained while adjusting the emission color. Furthermore, the diarylamine groups are preferably bonded to positions symmetrical with respect to the light emitter. Using this structure, fluorescent materials with high quantum yields can be realized.

[0160] Alternatively, the protecting group can be bonded to the luminescent body via the aryl group of the diarylamine, instead of directly bonding the protecting group to the luminescent body. By employing this structure, the protecting group can be configured to cover the luminescent body, thus allowing for a longer distance between the host material and the luminescent body in all directions, which is preferable. Furthermore, when the protecting group is not directly bonded to the luminescent body, it is preferable to bond four or more protecting groups relative to one luminescent body.

[0161] Furthermore, as shown in Figures 3A and 3B, preferably, at least one of the atoms constituting the multiple protecting groups is located directly on the luminescent body, that is, directly on one face of the fused aromatic ring or the fused heteroaromatic ring, and at least one of the atoms constituting the multiple protecting groups is located directly on the other face of the fused aromatic ring or the fused heteroaromatic ring. As a specific method, the following structure can be cited: That is, the fused aromatic ring or the fused heteroaromatic ring of the luminescent body is bonded to two or more diphenylamino groups, wherein the phenyl groups in the two or more diphenylamino groups each have protecting groups independently at the 3- and 5-positions.

[0162] By employing such a structure, as shown in Figures 3A and 3B, it is possible to achieve a configuration where the protecting group at the 3- or 5-position of the phenyl group is located directly above the fused aromatic ring or fused heteroaromatic ring of the luminescent organism. As a result, the surface above and below the fused aromatic ring or fused heteroaromatic ring can be efficiently covered, suppressing energy transfer based on the Dexter mechanism.

[0163] As energy acceptor materials as described above, organic compounds represented by the following general formulas (G1) or (G2) can be used, for example.

[0164] [Chemical Formula 2]

[0165] In general formulas (G1) and (G2), A represents a substituted or unsubstituted fused aromatic ring or a substituted or unsubstituted heteroaromatic ring having 10 to 30 carbon atoms; Ar1 ​​to Ar6 each independently represent a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; X1 to X12 each independently represent any one of a branched alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, or a trialkylsilyl group having 3 or more but less than 10 carbon atoms; and R1 to R10 each independently represent any one of hydrogen, an alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, or a trialkylsilyl group having 3 or more but less than 12 carbon atoms.

[0166] Examples of aromatic groups with 6 to 13 carbon atoms include phenyl, biphenyl, naphthyl, and geniyl. Note that the aromatic group is not limited to these. Furthermore, when the aromatic group has a substituent, examples of such substituents include alkyl groups with 1 to 7 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, tertiary butyl, pentyl, and hexyl; cyclopentyl, cyclohexyl, and cycloheptyl groups with 5 to 7 carbon atoms such as 8,9,10-trinorbornel; and aryl groups with 6 to 12 carbon atoms such as phenyl, naphthyl, and biphenyl.

[0167] In general formula (G1), a substituted or unsubstituted fused aromatic ring with 10 to 30 carbon atoms or a substituted or unsubstituted fused heteroaromatic ring with 10 to 30 carbon atoms represents the above-mentioned luminescent material, and the above-mentioned skeleton can be used. Furthermore, in general formulas (G1) and (G2), X1 to X12 represent protecting groups.

[0168] In general formula (G2), the protecting group is bonded to the quinacridone skeleton of the luminescent organism via an aryl group. By employing this structure, the protecting group can be configured to cover the luminescent organism, thus suppressing energy transfer based on the Dexter mechanism. Alternatively, a protecting group can be directly bonded to the luminescent organism.

[0169] Organic compounds represented by the following general formula (G3) or (G4) can be used as the energy acceptor material.

[0170] [Chemical Formula 3]

[0171] In general formulas (G3) and (G4), A represents a substituted or unsubstituted fused aromatic ring or a substituted or unsubstituted heteroaromatic ring having 10 to 30 carbon atoms, and X1 to X12 independently represent any one of a branched alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, and a trialkylsilyl group having 3 or more but less than 10 carbon atoms.

[0172] The protecting group is preferably bonded to the luminescent body via an extended phenyl group. By employing this structure, the protecting group can be configured to cover the luminescent body, thus suppressing energy transfer based on the Dexter mechanism. Furthermore, when the luminescent body and the protecting group are bonded via an extended phenyl group and both protecting groups are bonded to the extended phenyl group, as shown in general formulas (G3) and (G4), the two protecting groups are preferably bonded to the extended phenyl group in a meta-position. By employing this structure, the luminescent body can be efficiently covered, thus suppressing energy transfer based on the Dexter mechanism. An example of an organic compound represented by general formula (G3) is the aforementioned 2tBu-mmtBuDPhA2Anth. That is, in one embodiment of the invention, general formula (G3) is a particularly preferred example.

[0173] Organic compounds represented by the following general formula (G5) can be used as the energy acceptor material.

[0174] [Chemical Formula 4]

[0175] In general formula (G5), X1 to X8 independently represent any one of a branched alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, and a trialkylsilyl group having 3 or more but less than 10 carbon atoms, respectively; R11 to R18 independently represent any one of hydrogen, a branched alkyl group having 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more but less than 10 carbon atoms, a trialkylsilyl group having 3 or more but less than 10 carbon atoms, and an aryl group having 6 or more but less than 25 carbon atoms, respectively.

[0176] Examples of aryl groups having 6 or more but 25 or fewer carbon atoms include phenyl, naphthyl, biphenyl, geniyl, and spirogeniyl. Note that the number of aryl groups having 6 or more but 25 or fewer carbon atoms is not limited to these. Furthermore, when the aryl group has a substituent, examples of substituents include alkyl groups having 1 or more but 10 or fewer carbon atoms, branched alkyl groups having 3 or more but 10 or fewer carbon atoms, substituted or unsubstituted cycloalkyl groups having 3 or more but 10 or fewer carbon atoms, and trialkylsilyl groups having 3 or more but 10 or fewer carbon atoms.

[0177] Anthracene compounds exhibit high luminescence quantum yields and small luminescent areas, allowing for efficient coverage of the anthracene surface both above and below by protecting groups. An example of an organic compound represented by the general formula (G5) is the aforementioned 2tBu-mmtBuDPhA2Anth.

[0178] Hereinafter, examples of compounds described in general formulas (G1) to (G5) are shown by structural formulas (102) to (105) and (200) to (284). Note that the compounds described in general formulas (G1) to (G5) are not limited thereto. Furthermore, the compounds shown by structural formulas (102) to (105) and (200) to (284) can be suitably used as guest materials for a light-emitting element according to one embodiment of the present invention. Note that the guest material is not limited thereto.

[0179] [Chemical Formula 5]

[0180] [Chemical Formula 6]

[0181] [Chemical Formula 7]

[0182] [Chemical Formula 8]

[0183] [Chemical Formula 9]

[0184] [Chemical Formula 10]

[0185] [Chemical Formula 11]

[0186] [Chemical Formula 12]

[0187] [Chemical Formula 13]

[0188] [Chemical Formula 14]

[0189] [Chemical Formula 15]

[0190] [Chemical Formula 16]

[0191] [Chemical Formula 17] [Chemical Formula 18]

[0192] [Chemical Formula 19]

[0193] [Chemical Formula 20]

[0194] [Chemical Formula 21]

[0195] [Chemical Formula 22]

[0196] [Chemical Formula 23]

[0197] [Chemical Formula 24]

[0198] [Chemical Formula 25]

[0199] [Chemical Formula 26]

[0200] Examples of guest materials, represented by structural formulas (100) and (101), that can be suitably used as a light-emitting element in one embodiment of the present invention. Note that the guest material is not limited thereto.

[0201] [Chemical Formula 27]

[0202] When compound 133 is used as an energy donor, a TADF material can be used, for example. Preferably, the energy difference between the S1 and T1 energy levels of compound 133 is small, specifically greater than 0 eV and less than 0.2 eV. Alternatively, a TADF material can also be used as compound 136.

[0203] Compounds 133 and / or 136 preferably comprise a skeleton with hole transport capability and a skeleton with electron transport capability. Alternatively, compounds 133 and / or 136 preferably comprise a π-electron-rich skeleton or an aromatic amine skeleton and a π-electron-deficient skeleton. This facilitates the formation of donor-acceptor type excited states within the molecule. Furthermore, it is preferable to include a structure in which the electron transport skeleton and the hole transport skeleton are directly bonded, thereby simultaneously enhancing the donor and acceptor properties in the molecules of compounds 133 and / or 136. Alternatively, it is preferable to include a structure in which the π-electron-rich skeleton or the aromatic amine skeleton is directly bonded to the π-electron-deficient skeleton. By simultaneously enhancing the donor and acceptor properties within the molecule, the overlap between the molecular orbital distribution regions of HOMO and LUMO can be reduced in compounds 133 and / or 136, thereby reducing the energy difference between the singlet and triplet excitation levels of compounds 133 and / or 136. In addition, the triplet excitation energy levels of compounds 133 and / or 136 can be kept high.

[0204] When TADF material is composed of one material, for example, the following materials can be used.

[0205] First, examples include fullerenes or their derivatives, acridine derivatives such as proflavin, and eosin. Additionally, examples include metalloporphyrins containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd). Examples of metal-containing porphyrins include protoporphyrin-tin fluoride complexes (SnF2(Proto IX)), mesoporphyrin-tin fluoride complexes (SnF2(Meso IX)), hematoporphyrin-tin fluoride complexes (SnF2(Hemato IX)), coproporphyrin tetramethyl ester-tin fluoride complexes (SnF2(Copro III-4Me)), octaethylporphyrin-tin fluoride complexes (SnF2(OEP)), protoporphyrin-tin fluoride complexes (SnF2(Etio I)), and octaethylporphyrin-platinum chloride complexes (PtCl2OEP).

[0206] [Chemical Formula 28]

[0207] In addition, as a TADF material composed of a single material, heterocyclic compounds with one or both of a π-electron-rich backbone and a π-electron-deficient backbone can also be used. Specifically, examples include 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazole-11-yl)-1,3,5-triazine (abbreviated: PIC-TRZ), 2-{4-[3-(N-phenyl-9H-carbazole-3-yl)-9H-carbazole-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviated: PCCzPTzn), 2 -[4-(10H-phenanthroline-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PXZ-TRZ), 3-[4-(5-phenyl-5,10-dihydrophenanthroline-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviation: PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-oxanthracene-9 - Ketone (abbreviation: ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacrimidine)phenyl] phenazine (abbreviation: DMAC-DPS), 10-phenyl-10H,10'H-spiro[acrimidine-9,9'-anthracene]-10'-one (abbreviation: ACRSA), 4-(9'-phenyl-3,3'-bi-9H-carbazole-9-yl)benzofuran[3,2-d]pyrimidine (abbreviation: Examples of heterocyclic compounds include 4PCCzBfpm, 4-[4-(9'-phenyl-3,3'-bi-9H-carbazole-9-yl)phenyl]benzofuran[3,2-d]pyrimidine (abbreviated as: 4PCCzPBfpm), and 9-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9'-phenyl-2,3'-bi-9H-carbazole (abbreviated as: mPCCzPTzn-02). These heterocyclic compounds possess both π-electron-rich and π-electron-deficient heteroaromatic rings, resulting in high electron and hole transport properties, making them preferred. In particular, among the skeletons with π-electron-deficient heteroaromatic rings, pyridine, diazine (pyrimidine, pyrazine, and triazine) skeletons are stable and reliable, thus being preferred. In particular, benzofuran-pyrimidine skeletons, benzothiophene-pyrimidine skeletons, benzofuran-pyrazine skeletons, and benzothiophene-pyrazine skeletons exhibit high acceptor activity and good reliability, and are therefore preferred. Furthermore, among skeletons with π-electron-rich heteroaromatic rings, acridine skeletons, phenanthrene skeletons, phenanthrene-thiophene skeletons, furan skeletons, thiophene skeletons, and pyrrole skeletons are stable and have good reliability, and it is preferred to have at least one of the above skeletons. Additionally, dibenzofuran skeletons are preferred as furan skeletons, and dibenzothiophene skeletons are preferred as thiophene skeletons. As pyrrole skeletons, indole skeletons, carbazole skeletons, bicarbazole skeletons, and 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeletons are particularly preferred.Furthermore, in substances where π-electron-rich and π-electron-deficient heteroaromatic rings are directly bonded, the π-electron-rich heteroaromatic ring exhibits strong donor and acceptor properties, and the energy difference between the singlet and triplet excited states is smaller, making it particularly preferable. Alternatively, aromatic rings bonded with electron-withdrawing groups such as cyano groups can be used instead of π-electron-deficient heteroaromatic rings.

[0208] [Chemical Formula 29]

[0209] When compound 133 does not have the function of converting triplet excitation energy into luminescence, the combination of compound 131 and compound 133 is preferably a combination that forms an excited-state complex with each other, but there are no particular restrictions. Preferably, one has the function of transporting electrons and the other has the function of transporting holes.

[0210] Compound 131 can be categorized in addition to zinc and aluminum metal complexes, including diazole derivatives, triazole derivatives, benzimidazole derivatives, quinoline derivatives, dibenzoquinoline derivatives, dibenzothiophene derivatives, dibenzofuran derivatives, pyrimidine derivatives, triazine derivatives, pyridine derivatives, bipyridine derivatives, and phenoline derivatives. Other examples include aromatic amines or carbazole derivatives.

[0211] In addition, materials with high electrical conductivity and high electron conductivity can be used, for example.

[0212] As a hole-transporting material, materials with higher hole transport properties than electron transport properties can be used, preferably materials with a hole mobility of 1×10⁻⁶ cm² / Vs or higher. Specifically, aromatic amines, carbazole derivatives, aromatic hydrocarbons, stilbene derivatives, etc., can be used. The aforementioned hole-transporting materials can also be polymer compounds.

[0213] Materials with high hole transport properties, for example, as aromatic amine compounds, include N,N'-bis(p-tolyl)-N,N'-diphenyl-p-phenylenediamine (DTDPPA), 4,4'-bis[N-(4-diphenylaminophenyl)-N-anilino]biphenyl (DPAB), N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (DNTPD), and 1,3,5-tris[N-(4-diphenylaminophenyl)-N-anilino]benzene (DPA3B), etc.

[0214] In addition, as carbazole derivatives, specifically examples include 3-[N-(4-diphenylaminophenyl)-N-anilino]-9-phenylcarbazole (abbreviated as: PCzDPA1), 3,6-bis[N-(4-diphenylaminophenyl)-N-anilino]-9-phenylcarbazole (abbreviated as: PCzDPA2), and 3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviated as: PCzDPA2). Examples of such products include PCzTPN2, 3-[N-(9-phenylcarbazole-3-yl)-N-anilino]-9-phenylcarbazole (abbreviated as PCzPCA1), 3,6-bis[N-(9-phenylcarbazole-3-yl)-N-anilino]-9-phenylcarbazole (abbreviated as PCzPCA2), and 3-[N-(1-naphthyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole (abbreviated as PCzPCN1).

[0215] In addition, other examples of carbazole derivatives include 4,4'-bis(N-carbazolyl)biphenyl (abbreviated as CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviated as TCPB), 9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole (abbreviated as CzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

[0216] Examples of aromatic hydrocarbons include 2-tertiary butyl-9,10-bis(2-naphthyl)anthracene (t-BuDNA), 2-tertiary butyl-9,10-bis(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 2-tertiary butyl-9,10-bis(4-phenylphenyl)anthracene (t-BuDBA), 9,10-bis(2-naphthyl)anthracene (DNA), 9,10-diphenylanthracene (DPAnth), 2-tertiary butylanthracene (t-BuAnth), and 9,10-bis(4-methyl-1-naphthyl)anthracene (DMNA). Anthracene, 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-bis(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-bis(2-naphthyl)anthracene, 9,9'-bianthracene, 10,10'-diphenyl-9,9'-bianthracene, 10,10'-bis(2-phenylphenyl)-9,9'-bianthracene, 10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthracene, anthracene, condensed tetraphenylene, red fluorene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, etc. In addition, condensed pentaphenylene, keratin, etc., can also be used. Therefore, it is preferable to use aromatic hydrocarbons with a hole mobility of 1×10⁻⁶ cm² / Vs or higher and a carbon number of 14 to 42.

[0217] Note that aromatic hydrocarbons can also have a vinyl skeleton. Examples of aromatic hydrocarbons with vinyl skeletons include 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviated as DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviated as DPVPA).

[0218] Alternatively, high molecular weight compounds such as poly(N-vinylcarbazole) (PVK), poly(4-vinyltriphenylamine) (PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide] (PTPDMA), and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (Poly-TPD) can also be used.

[0219] In addition, materials with high hole transport properties, for example, 4,4'-bis[N-(1-naphthyl)-N-anilino]biphenyl (abbreviated as NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviated as TPD), 4,4',4''-tris(carbazole-9-yl)triphenylamine (abbreviated as TCTA), 4,4',4''-tris[N-(1-naphthyl)-N-anilino]triphenylamine (abbreviated as 1'-TNATA), 4,4',4''-tris(N,N-diphenylamino)triphenylamine (abbreviated as TDATA), and 4,4',4''-tris[N-(3-methylphenyl)-N-anilino] Triphenylamine (MTDATA), 4,4'-bis[N-(spiro-9,9'-bifuran-2-yl)-N-anilino]biphenyl (BSPB), 4-phenyl-4'-(9-phenylfuran-9-yl)triphenylamine (BPAFLP), 4-phenyl-3'-(9-phenylfuran-9-yl)triphenylamine (mBPAFLP), N-(9,9-dimethyl-9H-furan-2-yl)-N-{(9,9-dimethyl-2-[N'-phenyl-N'-(9,9-dimethyl-9H-furan-2-yl)amino]-9H-furan-7-yl}phenylamine (DFLADFL), N-(9,9-dimethyl-2-diphenylamino-9H-furan-7-yl)diphenylamine 2-[N-(4-diphenylaminophenyl)-N-anilino]spiro-9,9'-biphenylamine (DPASF), 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (PCBA1BP), 4,4'-diphenyl-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (PCBANB), 4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (PCBNBB), 4-phenyldiphenyl-(9-phenyl-9H-) N,N'-bis(9-phenylcarbazole-3-yl)amine (abbreviation: PCA1BP), N,N'-bis(9-phenylcarbazole-3-yl)-N,N'-diphenylphenyl-1,3-diamine (abbreviation: PCA2B), N,N',N''-triphenyl-N,N',N''-tris(9-phenylcarbazole-3-yl)phenyl-1,3,5-triamine (abbreviation: PCA3B), N-(4-biphenyl)-N-(9,9-dimethyl-9H-furo-2-yl)-9-phenyl-9H-carbazole-3-amine (abbreviation: PCBiF), N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9,9-dimethyl-9H-furo-2-amine (abbreviation: PCBBiF), 9,9-Dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-2-amine (abbreviated: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifuran-2-amine (abbreviated: PCBASF), 2-[N-(9-phenylcarbazol-3-yl)-N-anilino]spiro-9,9'-bifuran (abbreviated: PCASF), 2,7 Aromatic amine compounds such as bis[N-(4-diphenylaminophenyl)-N-anilino]spiro-9,9'-bifuran (abbreviated as: DPA2SF), N-[4-(9H-carbazole-9-yl)phenyl]-N-(4-phenyl)phenylaniline (abbreviated as: YGA1BP), and N,N'-bis[4-(carbazole-9-yl)phenyl]-N,N'-diphenyl-9,9-dimethylfuran-2,7-diamine (abbreviated as: YGA2F) are among the most common. Alternatively, 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviated as PCPN), 3-[4-(9-phenanthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviated as PCPPn), 3,3'-bis(9-phenyl-9H-carbazole) (abbreviated as PCCP), 1,3-bis(N-carbazolyl)phenyl (abbreviated as mCP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviated as CzTP), 4-{(3-[3-(9-phenyl-9H-en-9-yl)phenyl]phenyl}dibenzofuran (abbreviated as mmDBFFLBi-II), 4,4',4''-(benzene-1,3,5-triyl)tris(dibenzofuran) (abbreviated as mmDBFFLBi-II) The list includes amine compounds such as DBF3P-II, 1,3,5-tris(dibenzothiophene-4-yl)benzene (DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-en-9-yl)phenyl]dibenzothiophene (DBTFLP-III), 4-[4-(9-phenyl-9H-en-9-yl)phenyl]-6-phenyldibenzothiophene (DBTFLP-IV), and 4-[3-(triphenyl-2-yl)phenyl]dibenzothiophene (mDBTPTp-II), as well as carbazole compounds, thiophene compounds, furan compounds, enantiophene compounds, triphenylbenzene compounds, and phenanthrene compounds. The substances described herein are primarily those with a hole mobility of 1 × 10⁻⁶ cm² / Vs or higher. However, any substance other than those listed above can be used if its hole transport capability is higher than its electron transport capability.

[0220] As electron transport materials, materials with higher electron transport than hole transport can be used, preferably materials with an electron mobility of 1 × 10⁻⁶ cm² / Vs or higher. As materials that readily accept electrons (materials with electron transport properties), π-electron-deficient heteroaromatic compounds or metal complexes containing nitrogen-containing heteroaromatic compounds can be used. Specific examples include metal complexes containing quinoline ligands, benzoquinoline ligands, acetazole ligands, or thiazole ligands, acediazole derivatives, triazole derivatives, phenobarbital derivatives, pyridine derivatives, bipyridine derivatives, and pyrimidine derivatives.

[0221] For example, metal complexes with quinoline or benzoquinoline skeletons, such as tris(8-hydroxyquinoline)aluminum(III) (abbreviated: Alq), tris(4-methyl-8-hydroxyquinoline)aluminum(III) (abbreviated: Almq 3), bis(10-hydroxybenzo[h]quinoline)beryllium(II) (abbreviated: BeBq 2), bis(2-methyl-8-hydroxyquinoline)(4-phenylphenol)aluminum(III) (abbreviated: BAlq), and bis(8-hydroxyquinoline)zinc(II) (abbreviated: Znq), can be used. In addition, metal complexes with acetazole or thiazole ligands, such as bis[2-(2-benzoacetazole)phenol]zinc(II) (abbreviated: ZnPBO) and bis[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated: ZnBTZ), can also be used.Furthermore, besides metal complexes, other compounds that can be used include 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-diazole (abbreviated as PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-diazole-2-yl]benzene (abbreviated as OXD-7), 9-[4-(5-phenyl-1,3,4-diazole-2-yl)phenyl]-9H-carbazole (abbreviated as CO11), 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviated as TAZ), 2,2',2''-(1,3,5-phenyltriyl)tris(1-phenyl-1H-benzimidazole) (abbreviated as TPBI), and 2-[3-(dibenzothiophene-4-diphenyltriphenyl)-4-diphenyltri ... Heterocyclic compounds such as [-(dibenzothiophene-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II), ruberin (abbreviation: BPhen), 2,9-bis(naphthyl-2-yl)-4,7-diphenyl-1,10-benzimidazole (abbreviation: NBPhen), and copper sulfate (abbreviation: BCP); 2-[3'-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline (abbreviation: 2mDBTPDBq-II), 2-[3'-(dibenzothiophene-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoline (abbreviation: 2mDBTBPDBq-II), 2-[3'-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoline (abbreviation: 2m... CzBPDBq), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline (abbreviation: 7mDBTPDBq-II), 6-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline (abbreviation: 6mDBTPDBq-II), 4,6-bis[3-(phenanthrene-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothiophene)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II), 4,6-bis[3-(9H-9-yl)phenyl]pyrimidine Heterocyclic compounds with a diazine skeleton, such as 4,6mCzP2Pm, 2-{4-[3-(N-phenyl-9H-carbazole-3-yl)-9H-carbazole-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (PCCzPTzn), 3,5-bis[3-(9H-carbazole-9-yl)phenyl]pyridine (35DCzPPy) and 1,3,5-tris[3-(3-pyridyl)phenyl]benzene (TmPyPB), 4,4'-bis(5-methylbenzozo-2-yl)stilbene (BzOs).Alternatively, polymeric compounds such as poly(2,5-pyridindiyl) (abbreviated as PPy), poly[(9,9-dihexylenazine-2,7-diyl)-co-(pyridin-3,5-diyl)] (abbreviated as PF-Py), and poly[(9,9-dioctylenazine-2,7-diyl)-co-(2,2'-bipyridin-6,6'-diyl)] (abbreviated as PF-BPy) can also be used. The substances described here are primarily those with an electron mobility of 1 × 10⁻⁶ cm² / Vs or higher. Note that any substance other than those mentioned above can be used as long as its electron transport capacity is higher than its hole transport capacity.

[0222] Compound 133 is preferably a material capable of forming an excited-state complex with compound 131. Specifically, hole-transporting materials and electron-transporting materials as described above can be used. In this case, compounds 131 and 133, as well as compound 132 (fluorescent material), are selected such that the emission peak of the excited-state complex formed by compounds 131 and 133 overlaps with the absorption band of the longest wavelength side (low energy side) of compound 132 (fluorescent material). Thus, a light-emitting element with significantly improved luminous efficiency can be achieved.

[0223] Phosphorescent materials can be used as compounds 133 and / or 136. Examples of phosphorescent materials include iridium, rhodium, platinum-based organometallic complexes or metal complexes. Additionally, examples include platinum complexes or organoiridium complexes with porphyrin ligands, and, in particular, organoiridium complexes such as ortho-metal complexes with iridium ligands are preferred. Examples of ortho-metallized ligands include 4H-triazole ligands, 1H-triazole ligands, imidazole ligands, pyridine ligands, pyrimidine ligands, pyrazine ligands, or isoquinoline ligands. In this case, compound 133 (phosphorescent material) has an absorption band with a triple MLCT (metal-to-ligand charge transfer) transition. Furthermore, it is preferable to select compounds 133 and 132 (fluorescent material) such that the emission peak of compound 133 overlaps with the absorption band of compound 132 (fluorescent material) on the longest wavelength side (low energy side). Thus, a light-emitting element with significantly improved luminous efficiency can be achieved. Furthermore, even when compound 133 is a phosphorescent material, it can form an excited-state complex with compound 131. When an excited-state complex is formed, the phosphorescent material does not need to emit light at room temperature; it only needs to emit light at room temperature when the excited-state complex is formed. In this case, for example, tris[2-(1H-pyrazol-1-yl-κN2)phenyl-κC]iridium(III) (abbreviated as Ir(ppz)3) can be used as the phosphorescent material. Moreover, it is preferable to select compounds 132 and 136 such that the emission peak of compound 132 overlaps with the absorption band of the longest wavelength side (low energy side) of compound 136. Thus, a multicolor light-emitting element with good luminous efficiency can be manufactured.

[0224] Examples of substances that exhibit emission peaks in the blue or green wavelength regions include tri{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviated as Ir(mpptz-dmp)3), tri(5-methyl-3,4-diphenyl-4H-1,2,4-triazole)iridium(III) (abbreviated as Ir(Mptz)3), tri[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazole]iridium(III) (abbreviated as Ir(iPrptz-3b)3), and tri[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazole]iridium(III) (abbreviated as Ir(iPr5btz)). 3) Organometallic iridium complexes with a 4H-triazole skeleton, such as tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazole]iridium(III) (abbreviated as: Ir(Mptz1-mp)3), tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole)iridium(III) (abbreviated as: Ir(Prptz1-Me)3), and other organometallic iridium complexes with a 1H-triazole skeleton; fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazolium]iridium(III) (abbreviated as: Ir(iPrpmi)3), tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviated as: Ir(dmpimpt-Me) 3) Organometallic iridium complexes with an imidazole skeleton; and organometallic iridium complexes with phenylpyridine derivatives having electron-withdrawing groups as ligands, such as bis[2-(4',6'-difluorophenyl)pyridinium-N,C 2']iridium(III)tetra(1-pyrazolyl)borate (abbreviated as: FIr6), bis[2-(4',6'-difluorophenyl)pyridinium-N,C 2']iridium(III)pyridinecarboxylate (abbreviated as: FIrpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinium-N,C 2'}iridium(III)pyridinecarboxylate (abbreviated as: Ir(CF 3ppy) 2(pic)), and bis[2-(4',6'-difluorophenyl)pyridinium-N,C 2']iridium(III)acetoacetone (abbreviated as: FIr(acac)). Among the above materials, organometallic iridium complexes with nitrogen-containing five-membered heterocyclic skeletons such as 4H-triazole skeleton, 1H-triazole skeleton and imidazole skeleton have high triple excitation energy and high reliability and high luminescence efficiency, so they are particularly superior.

[0225] Examples of substances that exhibit emission peaks in the green or yellow wavelength regions include tris(4-methyl-6-phenylpyrimidine)iridium(III) (abbreviated as Ir(mppm) 3), tris(4-tert-butyl-6-phenylpyrimidine)iridium(III) (abbreviated as Ir(tBuppm) 3), (acetylacetone)bis(6-methyl-4-phenylpyrimidine)iridium(III) (abbreviated as Ir(mppm) 2(acac)), (acetylacetone)bis(6-tert-butyl-4-phenylpyrimidine)iridium(III) (abbreviated as Ir(tBuppm) 2(acac)), and (acetylacetone)bis[4-(2-norborneol)-6-phenylpyrimidine]iridium(III) (abbreviated as Ir(nbppm)). Organometallic iridium complexes with a pyrimidine skeleton, such as 2(acac)), (acetylacetone)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidine]iridium(III) (abbreviated as: Ir(mpmppm) 2(acac)), (acetylacetone)bis{(4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}iridium(III) (abbreviated as: Ir(dmppm-dmp) 2(acac)), (acetylacetone)bis(4,6-diphenylpyrimidine)iridium(III) (abbreviated as: Ir(dppm) 2(acac)); and (acetylacetone)bis(3,5-dimethyl-2-phenylpyrazine)iridium(III) (abbreviated as: Ir(mppr-Me)). Organometallic iridium complexes with a pyrazine skeleton, such as 2(acac) and (acetylacetone)bis(5-isopropyl-3-methyl-2-phenylpyrazine)iridium(III) (abbreviated as: Ir(mppr-iPr) 2(acac)); tri(2-phenylpyridin-N,C 2')iridium(III) (abbreviated as: Ir(ppy) 3), bis(2-phenylpyridin-N,C 2')iridium(III)acetylacetone (abbreviated as: Ir(ppy) 2(acac)), bis(benzo[h]quinoline)iridium(III)acetylacetone (abbreviated as: Ir(bzq) 2(acac)), tri(benzo[h]quinoline)iridium(III) (abbreviated as: Ir(bzq) 3), tri(2-phenylquinoline-N,C 2')iridium(III) (abbreviated as: Ir(pq) 3), bis(2-phenylquinoline-N,C 2') Iridium(III) acetoacetone (abbreviated as: Ir(pq) 2(acac)) and other organometallic iridium complexes with a pyridine framework;Organometallic iridium complexes such as bis(2,4-diphenyl-1,3-azol-N,C 2')iridium(III)acetoacetone (abbreviated as: Ir(dpo) 2(acac)), bis{2-[4'-(perfluorophenyl)phenyl]pyridine-N,C 2'}iridium(III)acetoacetone (abbreviated as: Ir(p-PF-ph) 2(acac)), and bis(2-phenylbenzothiazole-N,C 2')iridium(III)acetoacetone (abbreviated as: Ir(bt) 2(acac)) are examples; rare earth metal complexes such as tri(acetoacetone-(monoporphyrin) terbium(III) (abbreviated as: Tb(acac) 3(Phen)) are also examples. Among these materials, organometallic iridium complexes with a pyrimidine framework are particularly preferred due to their very high reliability and luminescent efficiency.

[0226] In addition, examples of substances exhibiting emission peaks in the yellow or red wavelength regions include organometallic iridium complexes with a pyrimidine skeleton, such as (diisobutylmethane)bis[4,6-bis(3-methylphenyl)pyrimidinium]iridium(III) (abbreviated as: Ir(5mdppm) 2(dibm)), bis[4,6-bis(3-methylphenyl)pyrimidinium](dineopentylmethane)iridium(III) (abbreviated as: Ir(5mdppm) 2(dpm)), and bis[4,6-bis(naphthyl-1-yl)pyrimidinium](dineopentylmethane)iridium(III) (abbreviated as: Ir(d1npm) 2(dpm)); and (acetylacetone)bis(2,3,5-triphenylpyrazine)iridium(III) (abbreviated as: Ir(tppr)). Organometallic iridium complexes with a pyrazine skeleton, such as 2(acac)), bis(2,3,5-triphenylpyrazine)(dineoptiacrylmethyl)iridium(III) (abbreviated as: Ir(tppr) 2(dpm)), (acetylacetone)bis[2,3-bis(4-fluorophenyl)quinoline]iridium(III) (abbreviated as: Ir(Fdpq) 2(acac)), bis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}(2,2',6,6'-tetramethyl-3,5-heptanedione-κ 2O,O')iridium(III) (abbreviated as: Ir(dmdppr-dmp) 2(dpm)); tri(1-phenylisoquinoline-N,C Organometallic iridium complexes with a pyridine skeleton, such as iridium(III) (abbreviated as Ir(piq) 3) and bis(1-phenylisoquinoline-N,C 2')iridium(III)acetophenone (abbreviated as Ir(piq) 2(acac)); platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviated as PtOEP); and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato) (monoporphyrin) europium(III) (abbreviated as Eu(DBM) 3(Phen)) and tris[1-(2-thiophenecarboxyl)-3,3,3-trifluoroacetophenone] (monoporphyrin) europium(III) (abbreviated as Eu(TTA) 3(Phen)). Among the aforementioned substances, organometallic iridium complexes with a pyrimidine framework are particularly preferred due to their very high reliability and luminescence efficiency. Furthermore, organometallic iridium complexes with a pyrazine framework can achieve red luminescence with excellent colorimetry.

[0227] Furthermore, metal halide perovskite materials can be cited as materials that can be used as the aforementioned energy donors. These metal halide perovskite materials can be represented by any one of the following general formulas (g1) to (g3).

[0228] (SA)MX 3:(g1) (LA) 2(SA) n-1M nX 3n + 1:(g2) (PA)(SA) n-1M nX3 n + 1:(g3)

[0229] In the above general formula, M represents a divalent metal ion and X represents a halide ion.

[0230] Specifically, divalent metal ions such as lead and tin are used as divalent cations.

[0231] Specifically, anions of chlorine, bromine, iodine, fluorine, etc., are used as halide ions.

[0232] Furthermore, although n represents an integer from 1 to 10, when n is greater than 10 in general formula (g2) or general formula (g3), its properties are similar to those of metal halide perovskite materials represented by general formula (g1).

[0233] In addition, LA represents ammonium ions represented as R 30-NH 3+.

[0234] In the ammonium ion represented by the general formula R 30-NH 3+, R 30 is: any one of an alkyl, aryl, or heteroaryl group having 2 to 20 carbon atoms; or a group formed by combining an alkylene group, aryl group, or heteroaryl group having 2 to 20 carbon atoms with an alkylene group, vinylene group, aryl group, or heteroaryl group having 1 to 12 carbon atoms. When the latter is true, multiple alkylene groups, vinylene groups, aryl groups, and heteroaryl groups can be linked together, or multiple groups of the same type can be used. When multiple alkylene groups, vinylene groups, aryl groups, and heteroaryl groups are linked together, the total number of alkylene groups, vinylene groups, aryl groups, and heteroaryl groups is preferably 35 or less.

[0235] SA represents a monovalent metal ion or an ammonium ion represented by R 31-NH 3+, where R 31 represents an alkyl group with 1 to 6 carbon atoms.

[0236] PA represents part or all of a branched polyethyleneimine containing an ammonium cation, such as NH3+-R32-NH3+, NH3+-R33-R34-R35-NH3+, or an ammonium cation, with a valence of +2. The charges in the general formula are almost balanced.

[0237] Here, the charge of metal halide perovskite materials does not necessarily need to be strictly balanced in all parts of the material according to the above general formula; it is sufficient to maintain the overall neutrality of the material. Sometimes, free ammonium ions, free halide ions, impurity ions, and other ions are locally present in the material, and sometimes they neutralize the charge. Furthermore, sometimes the surface of particles or films, grain boundaries, etc., are not locally neutral, and it is not necessary to maintain neutrality in all parts.

[0238] As for (LA) in the above general formula (g2), for example, substances represented by the following general formulas (a-1) to (a-11) and general formulas (b-1) to (b-6) can be used.

[0239] [Chemical Formula 30]

[0240] [Chemical Formula 31]

[0241] In the above general formula (g3), (PA) typically represents a portion or all of the substances represented by any of the following general formulas (c-1), (c-2), and (d), as well as branched polyethyleneimine containing ammonium cations, and has a +2 valence charge. These polymers sometimes neutralize the charge in multiple unit lattices, or sometimes each charge contained in two different polymer molecules neutralizes the charge in a single unit lattice.

[0242] [Chemical Formula 32]

[0243] [Chemical Formula 33]

[0244] However, in the above general formula, R 20 represents an alkyl group having 2 to 18 carbon atoms, R 21, R 22, and R 23 represent hydrogen or an alkyl group having 1 to 18 carbon atoms, and R 24 represents the following structural formulas and general formulas (R 24-1) to (R 24-14). R 25 and R 26 each independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms. X represents a combination of monomeric unit A and monomeric unit B represented by any one of (d-1) to (d-6) above, and has a structure including monomeric unit A and monomeric unit B, with the number of monomeric units A being u and the number of monomeric units B being v. Note that there is no restriction on the arrangement order of monomeric units A and B. m and l are both independent integers from 0 to 12, and t is an integer from 1 to 18. u is an integer from 0 to 17, v is an integer from 1 to 18, and u+v is an integer from 1 to 18.

[0245] [Chemical Formula 34]

[0246] Note that these are just examples, and the substances that can be used with (LA) and (PA) are not limited to these.

[0247] In three-dimensional metal halide perovskite materials with a composition represented by the general formula (g1) (SA)MX 3, a framework is formed by arranging regular octahedral structures with a metal atom M at the center and halogen atoms at the six vertices in a three-dimensional manner, sharing halogen atoms at each vertex. The aforementioned regular octahedral structural unit with halogen atoms at each vertex is called a perovskite unit. As structures, there are: zero-dimensional structures where the aforementioned perovskite units exist alone; linear structures where perovskite units are one-dimensionally connected by halogen atoms at the vertices; sheet-like structures where perovskite units are connected in two dimensions; and structures where perovskite units are connected in three dimensions. Furthermore, there are complex two-dimensional structures formed by stacking multiple sheet-like structures where perovskite units are connected in two dimensions. There are also even more complex structures. By definition, all these structures including perovskite units are collectively referred to as metal halide perovskite materials.

[0248] The light-emitting layer 130 can also be formed from two or more layers. For example, when the light-emitting layer 130 is formed by sequentially stacking a first light-emitting layer and a second light-emitting layer from the hole transport layer side, a material with hole transport properties can be used as the main material of the first light-emitting layer, and a material with electron transport properties can be used as the main material of the second light-emitting layer.

[0249] Furthermore, the luminescent layer 130 may also contain materials other than compounds 131, 132, and 133 (compound 135). In this case, to enable compounds 131 and 133 to efficiently form excited-state complexes, it is preferable that the HOMO level of one of compounds 131 and 133 is the highest among the materials in the luminescent layer 130, while the LUMO level of the other of compounds 131 and 132 is the lowest among the materials in the luminescent layer 130. By employing this energy level correlation, the reaction of excited-state complexes formed by compounds 131 and 135 can be suppressed.

[0250] For example, when compound 131 exhibits hole transport and compound 133 exhibits electron transport, it is preferable that the HOMO level of compound 131 is higher than the HOMO level of compound 133 and the HOMO level of compound 135, while the LUMO level of compound 133 is lower than the LUMO level of compound 131 and the LUMO level of compound 135. In this case, the LUMO level of compound 135 can be either higher or lower than the LUMO level of compound 131. Furthermore, the HOMO level of compound 135 can be either higher or lower than the HOMO level of compound 133.

[0251] While there are no particular limitations on the materials (compound 135) that can be used for the light-emitting layer 130, examples include: tris(8-hydroxyquinoline)aluminum(III) (abbreviated: Alq), tris(4-methyl-8-hydroxyquinoline)aluminum(III) (abbreviated: Almq 3), and bis(10-hydroxybenzo[h]quinoline)beryllium(II) (abbreviated: BeBq). 2) Metal complexes such as bis(2-methyl-8-hydroxyquinoline)(4-phenylphenol)aluminum(III) (abbreviated: BAlq), bis(8-hydroxyquinoline)zinc(II) (abbreviated: Znq), bis[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated: ZnPBO), and bis[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated: ZnBTZ); 2-(4-biphenyl)-5-(4-tertiary butylphenyl)-1,3,4-diazole (abbreviated: PBD), 1,3-bis[5-(p-tertiary butylphenyl)-1,3,4-diazole-2-yl]benzene (abbreviated: OXD-7), and 3-(4-biphenyl)-4-phenyl-5-(4-tertiary butylphenyl)-1,2,4-triazole (abbreviated: TAZ). Heterocyclic compounds such as 2,2',2''-(1,3,5-phenyltriyl)tris(1-phenyl-1H-benzimidazole) (abbreviated as TPBI), ruberin (abbreviated as BPhen), copper oxychloride (abbreviated as BCP), and 9-[4-(5-phenyl-1,3,4-diazol-2-yl)phenyl]-9H-carbazole (abbreviated as CO11); aromatic amine compounds such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated as NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviated as TPD), and 4,4'-bis[N-(spiro-9,9'-bifuro-2-yl)-N-phenylamino]biphenyl (abbreviated as BSPB). In addition, examples include anthracene derivatives, phenanthrene derivatives, pyrene derivatives, β derivatives, and dibenzo[g,p]β derivatives, which are condensed polycyclic aromatic compounds.Specifically, examples include 9,10-diphenylanthracene (DPAnth), N,N-diphenyl-9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole-3-amine (CzA1PA), 4-(10-phenyl-9-anthrayl)triphenylamine (DPhPA), 4-(9H-carbazole-9-yl)-4'-(10-phenyl-9-anthrayl)triphenylamine (YGAPA), and N,9-diphenyl-N-[4- [10-Pheny-9-Anthryl]phenyl]-9H-carbazole-3-amine (abbreviated: PCAPA), N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazole-3-amine (abbreviated: PCAPBA), N,9-diphenyl-N-(9,10-diphenyl-2-anthryl)-9H-carbazole-3-amine (abbreviated: 2PCAPA), 6,12-dimethoxy-5,11-diphenylamine, N,N,N' ,N',N'',N'',N''',N'''-Octaphenyldibenzo[g,p]π-2,7,10,15-tetramine (abbreviation: DBC1), 9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole (abbreviation: CzPA), 3,6-diphenyl-9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole (abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPP) A) 9,10-bis(2-naphthyl)anthracene (abbreviated as DNA), 2-tert-butyl-9,10-bis(2-naphthyl)anthracene (abbreviated as t-BuDNA), 9,9'-bianthracene (abbreviated as BANT), 9,9'-(stilbene-3,3'-diyl)phenanthrene (abbreviated as DPNS), 9,9'-(stilbene-4,4'-diyl)phenanthrene (abbreviated as DPNS2), and 1,3,5-tris(1-pyrene)benzene (abbreviated as TPB3), etc. From these substances and known substances, one or more substances with a band gap larger than that of compounds 131 and 132 can be selected.

[0252] <> Electrodes 101 and 102 have the function of injecting holes and electrons into the light-emitting layer 130. Electrodes 101 and 102 can be formed using metals, alloys, conductive compounds, and mixtures or stacks thereof. Typical examples of metals are aluminum (Al), in addition to transition metals such as silver (Ag), tungsten, chromium, molybdenum, copper, and titanium; alkali metals such as lithium (Li) or cesium; and Group 2 metals such as calcium or magnesium (Mg). Rare earth metals such as ytterbium (Yb) can also be used as transition metals. Alloys including the above-mentioned metals can be used, such as MgAg and AlLi. Conductive compounds include, for example, indium tin oxide (ITO), indium tin oxide containing silicon or silicon oxide (ITSO), indium zinc oxide, and indium oxide containing tungsten and zinc. Inorganic carbon materials such as graphene can also be used as conductive compounds. As described above, one or both of these materials can be formed by stacking multiple of them.

[0253] Furthermore, one or both of the light-emitting electrodes 101 and 102 obtained from the light-emitting layer 130 are extracted. Therefore, at least one of the electrodes 101 and 102 has the function of allowing visible light to pass through. Examples of conductive materials with light-transmitting function include those with a visible light transmittance of 40% or more and 100% or less, preferably 60% or more and 100% or less, and a resistivity of 1×10⁻² Ω·cm or less. Alternatively, the electrode on the light-extracting side can also be formed of a conductive material with both light-transmitting and light-reflecting functions. Examples of such conductive materials include those with a visible light reflectance of 20% or more and 80% or less, preferably 40% or more and 70% or less, and a resistivity of 1×10⁻² Ω·cm or less. When a material with low light transmittance, such as a metal or alloy, is used for the light-extracting electrode, one or both of the electrodes 101 and 102 can be formed with a thickness sufficient to allow visible light to pass through (e.g., a thickness of 1 nm to 10 nm).

[0254] Note that, in this specification, the electrode with light-transmitting function can be made of a material that is both conductive and allows visible light to pass through. Examples include oxide conductive layers represented by ITO (Indium Tin Oxide), oxide semiconductor layers, or organic conductive layers containing organic matter. Examples of organic conductive layers containing organic matter include layers comprising composite materials containing a mixture of organic compounds and electron donors, and layers comprising composite materials containing a mixture of organic compounds and electron acceptors. Furthermore, the resistivity of the transparent conductive layer is preferably 1 × 10⁵ Ω·cm or less, and more preferably 1 × 10⁴ Ω·cm or less.

[0255] In addition, sputtering, vapor deposition, printing, coating, MBE (Molecular Beam Epitaxy), CVD, pulsed laser deposition, ALD (Atomic Layer Deposition) and other methods can be used as film formation methods for electrodes 101 and 102.

[0256] <<Electric Hole Injection Layer>> The hole injection layer 111 has the function of reducing the injection energy barrier of holes from one of the pair of electrodes (electrode 101 or electrode 102) and promoting hole injection, and is formed, for example, using transition metal oxides, phthalocyanine derivatives, or aromatic amines. Examples of transition metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganese oxide. Examples of phthalocyanine derivatives include phthalocyanine or metallic phthalocyanine. Examples of aromatic amines include benzidine derivatives or phenylenediamine derivatives. Polymer compounds such as polythiophene or polyaniline can also be used, typically poly(ethyldioxythiophene) / poly(styrenesulfonic acid) as self-doped polythiophene.

[0257] As the hole injection layer 111, a layer comprising a composite material consisting of a hole-transporting material and a material having the property of receiving electrons from the hole-transporting material can be used. Alternatively, a stack of a layer containing a material having electron-receiving properties and a layer containing a hole-transporting material can be used. Charge transfer and acceptance can occur between these materials in a stationary state or in the presence of an electric field. Examples of materials having electron-receiving properties include organic acceptors such as quinone dimethane derivatives, tetrachlorobenzoquinone derivatives, and hexaazabenzene derivatives. Specifically, examples include compounds with electron-withdrawing groups (especially halogen groups such as fluorine groups and cyano groups), such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinone dimethylethane (F4-TCNQ), chloroquinone, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazabitribenzene (HAT-CN), and 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinone dimethylethane (F6-TCNNQ). In particular, compounds with electron-withdrawing groups bonded to fused aromatic rings with multiple heteroatoms, such as HAT-CN, are thermally stable and therefore preferred. In addition, electron-withdrawing groups (especially halogens such as fluorine groups and cyano groups) [3] axialene derivatives have very high electron acceptability and are therefore particularly preferred. Specifically, examples include: α,α',α''-1,2,3-cycloalkyltrimethylenetri[4-cyano-2,3,5,6-tetrafluorophenylacetonitrile], α,α',α''-1,2,3-cyclopropyltrimethylenetri[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)phenylacetonitrile], α,α',α''-1,2,3-cycloalkyltrimethylenetri[2,3,4,5,6-pentafluorophenylacetonitrile], etc. Furthermore, transition metal oxides, such as oxides of metals from Group 4 to Group 8, can be used. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, rhenium oxide, etc., can be used. Molybdenum oxide is particularly preferred because it is stable in the atmosphere, has low hygroscopicity, and is easy to handle.

[0258] As a hole transport material, materials with higher hole transport properties than electron transport properties can be used, preferably materials with a hole mobility of 1 × 10⁻⁶ cm² / Vs or higher. Specifically, aromatic amines and carbazole derivatives, which are examples of hole transport materials suitable for use in the luminescent layer 130, can be used. Additionally, aromatic hydrocarbons and stilbene derivatives can also be used. The aforementioned hole transport materials can also be polymeric compounds.

[0259] Examples of aromatic hydrocarbons include 2-tertiary butyl-9,10-bis(2-naphthyl)anthracene (t-BuDNA), 2-tertiary butyl-9,10-bis(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 2-tertiary butyl-9,10-bis(4-phenylphenyl)anthracene (t-BuDBA), 9,10-bis(2-naphthyl)anthracene (DNA), 9,10-diphenylanthracene (DPAnth), 2-tertiary butylanthracene (t-BuAnth), and 9,10-bis(4-methyl-1-naphthyl)anthracene (DMNA). Anthracene, 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-bis(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-bis(2-naphthyl)anthracene, 9,9'-bianthracene, 10,10'-diphenyl-9,9'-bianthracene, 10,10'-bis(2-phenylphenyl)-9,9'-bianthracene, 10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthracene, anthracene, condensed tetraphenylene, red fluorene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, etc. In addition, condensed pentaphenylene, keratin, etc., can also be used. Therefore, it is preferable to use aromatic hydrocarbons with a hole mobility of 1×10⁻⁶ cm² / Vs or higher and a carbon number of 14 to 42.

[0260] Note that aromatic hydrocarbons can also have a vinyl skeleton. Examples of aromatic hydrocarbons with vinyl skeletons include 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviated as DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviated as DPVPA).

[0261] Alternatively, high molecular weight compounds such as poly(N-vinylcarbazole) (PVK), poly(4-vinyltriphenylamine) (PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide] (PTPDMA), and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (Poly-TPD) can also be used.

[0262] <<Hole Transport Layer>> The hole transport layer 112 is a layer containing a hole transport material, and the material exemplified as that used in the hole injection layer 111 can be used. The hole transport layer 112 has the function of transporting holes injected into the hole injection layer 111 to the light emission layer 130, so it is preferably a HOMO level that is the same as or close to the HOMO level of the hole injection layer 111.

[0263] As the aforementioned hole transport material, the material exemplified as the material used in the hole injection layer 111 can be used. Furthermore, it is preferable to use a material having a hole mobility of 1 × 10⁻⁶ cm² / Vs or higher. However, any material other than the aforementioned material can be used, as long as its hole transport capability is higher than its electron transport capability. Additionally, the layer including the material with high hole transport capability is not limited to a single layer; two or more layers composed of the aforementioned material can also be stacked.

[0264] <<Electron Transport Layer>> The electron transport layer 118 functions to transport electrons injected from one of the pairs of electrodes (electrode 101 or electrode 102) through the electron injection layer 119 to the light-emitting layer 130. As the electron transport material, materials with higher electron transport than hole transport can be used, preferably materials with an electron mobility of 1×10⁻⁶ cm² / Vs or higher. As compounds that readily accept electrons (materials with electron transport), π-electron-deficient heteroaromatic compounds such as nitrogen-containing heteroaromatic compounds or metal complexes can be used. Specifically, examples of metal complexes containing quinoline ligands, benzoquinoline ligands, acetazole ligands, or thiazole ligands that can be used as electron transport materials for the light-emitting layer 130 include acediazole derivatives, triazole derivatives, phenobarbital derivatives, pyridine derivatives, bipyridine derivatives, and pyrimidine derivatives. Furthermore, substances with an electron mobility of 1×10⁻⁶ cm² / Vs or higher are preferred. However, as an electron transport layer, any material other than those mentioned above can be used, as long as its electron transport properties are higher than its hole transport properties. Furthermore, the electron transport layer 118 is not limited to a single layer; it can also consist of two or more layers composed of the aforementioned materials.

[0265] Additionally, a layer for controlling the movement of electron carriers can be provided between the electron transport layer 118 and the light-emitting layer 130. This layer for controlling the movement of electron carriers is a layer in which a small amount of a substance with high electron trapping capacity is added to the aforementioned material with high electron transport capacity. By suppressing the movement of electron carriers, the balance of carriers can be adjusted. This structure is very effective in suppressing problems caused by electrons passing through the light-emitting layer (such as a decrease in device lifetime).

[0266] <<Electron Injection Layer>> The electron injection layer 119 has the function of reducing the injection energy barrier of electrons from electrode 102 and promoting electron injection. For example, it can use group 1 metals, group 2 metals, or their oxides, halides, carbonates, etc. Composite materials of the aforementioned electron transport materials and materials having electron-donating properties can also be used. As materials with electron-donating properties, examples include group 1 metals, group 2 metals, or their oxides. Specifically, alkali metals, alkaline earth metals, or compounds of these metals such as lithium fluoride (LiF), sodium fluoride (NaF), cesium fluoride (CsF), calcium fluoride (CaF₂), and lithium oxide (LiOₓ) can be used. In addition, rare earth metal compounds such as erbium fluoride (ErF₃) can be used. In addition, electron salts can also be used in the electron injection layer 119. Examples of such electron salts include substances that add electrons at a high concentration to a mixed oxide of calcium and aluminum. In addition, substances that can be used in the electron transport layer 118 can also be used in the electron injection layer 119.

[0267] Alternatively, a composite material formed by mixing an organic compound with an electron donor can be used for the electron injection layer 119. This composite material exhibits excellent electron injection and electron transport properties because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material with excellent performance in transporting the generated electrons; specifically, for example, the substances constituting the electron transport layer 118 as described above (metal complexes, heteroaromatic compounds, etc.) can be used. As the electron donor, any substance that provides electrons to the organic compound is acceptable. Specifically, alkali metals, alkaline earth metals, and rare earth metals are preferred, such as lithium, cesium, magnesium, calcium, erbium, and ytterbium. Additionally, alkali metal oxides or alkaline earth metal oxides are preferred, such as lithium oxides, calcium oxides, and barium oxides. Furthermore, Lewisite such as magnesium oxide can also be used. Additionally, organic compounds such as tetrathiofulvalene (TTF) can also be used.

[0268] Furthermore, the aforementioned light-emitting layer, hole injection layer, hole transport layer, electron transport layer, and electron injection layer can all be formed by methods such as vapor deposition (including vacuum vapor deposition), inkjet printing, coating, nozzle printing, and gravure printing. In addition to the materials mentioned above, inorganic compounds such as quantum dots or polymeric compounds (oligomers, dendritic polymers, polymers, etc.) can also be used as the aforementioned light-emitting layer, hole injection layer, hole transport layer, electron transport layer, and electron injection layer.

[0269] As quantum dots, various types can be used, including colloidal quantum dots, alloy quantum dots, core-shell quantum dots, and nucleated quantum dots. Additionally, quantum dots containing elements from Groups 2 and 16, 13 and 15, 13 and 17, 11 and 17, or 14 and 15 can also be used. Alternatively, quantum dots containing elements such as cadmium (Cd), selenium (Se), zinc (Zn), sulfur (S), phosphorus (P), indium (In), tellurium (Te), lead (Pb), gallium (Ga), arsenic (As), and aluminum (Al) can be used.

[0270] As liquid media for wet processing, for example, ketones such as methyl ethyl ketone and cyclohexanone can be used; glycerol fatty acid esters such as ethyl acetate; halogenated aromatic hydrocarbons such as dichlorobenzene; aromatic hydrocarbons such as toluene, xylene, mesitylene, and cyclohexylbenzene; aliphatic hydrocarbons such as cyclohexane, decahydronaphthalene, and dodecane; and organic solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).

[0271] Examples of polymeric compounds that can be used in light-emitting layers include: poly(phenylenevinyl)ide (PPV) derivatives such as poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinyl] (abbreviated as MEH-PPV), poly(2,5-dioctyl-1,4-phenylenevinyl), etc.; poly(dioctylenevinyl) derivatives such as poly(9,9-di-n-octylenyl-2,7-diyl) (abbreviated as PF8), poly[(9,9-di-n-octylenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)] (abbreviated as F8BT), poly[( 9,9-Dioctyl-2,7-diyl)-alt-(2,2'-Bithiophene-5,5'-diyl)] (abbreviated as F8T2), poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-(9,10-anthracene)], poly[(9,9-dihexyl-2,7-diyl)-alt-(2,5-dimethyl-1,4-phenylene)], etc.; polyalkylthiophene (PAT) derivatives such as poly(3-hexylthiophene-2,5-diyl) (abbreviated as P3HT), polyphenylene derivatives, etc. Alternatively, the above-mentioned polymers, PVK, poly(2-vinylnaphthalene), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (abbreviated as PTAA), and other polymers can be doped with luminescent compounds and used as luminescent layers. As luminescent compounds, the luminescent compounds exemplified above can be used.

[0272] <<Substrate>> Furthermore, the light-emitting element of one embodiment of the present invention can be manufactured on a substrate made of glass, plastic, or the like. As for the order of stacking on the substrate, it can be stacked sequentially from either the electrode 101 side or the electrode 102 side.

[0273] Furthermore, as a substrate for forming the light-emitting element in one embodiment of the present invention, materials such as glass, quartz, or plastic can be used. Alternatively, a flexible substrate can also be used. A flexible substrate is a substrate that can be bent, such as a plastic substrate made of polycarbonate or polyarylate. Additionally, thin films or inorganic vapor-deposited thin films can be used. Note that other materials can be used as long as they function as a support in the manufacturing process of the light-emitting element and optical elements (color filters, etc.). Alternatively, any material that functions to protect the light-emitting element and optical elements is acceptable.

[0274] For example, various substrates can be used to form light-emitting elements in this specification. There are no particular limitations on the type of substrate. Examples of substrates include semiconductor substrates (e.g., single-crystal substrates or silicon substrates), SOI substrates, glass substrates, quartz substrates, plastic substrates, metal substrates, stainless steel substrates, substrates with stainless steel foil, tungsten substrates, substrates with tungsten foil, flexible substrates, laminated films, cellulose nanofibers (CNF) containing fibrous materials, paper, or substrate films. Examples of glass substrates include barium borosilicate glass, aluminum borosilicate glass, and soda-lime glass. Examples of flexible substrates, laminated films, and substrate films include plastics such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), and polytetrafluoroethylene (PTFE). Alternatively, resins such as acrylic resins can be used as examples. Alternatively, polypropylene, polyester, ethylene fluoride, or polyvinyl chloride can be used as examples. Alternatively, examples could include polyamide, polyimide, aromatic polyamide, epoxy resin, inorganic vapor-deposited films, and paper.

[0275] Alternatively, a flexible substrate can be used as the substrate, and the light-emitting element can be directly formed on the flexible substrate. Alternatively, a release layer can be provided between the substrate and the light-emitting element. A release layer can be used when part or all of the light-emitting element is fabricated on the release layer, and then it is separated from the substrate and transferred to another substrate. In this case, the light-emitting element can also be transferred to a substrate with low heat resistance or a flexible substrate. Furthermore, as the aforementioned release layer, for example, a laminated structure of inorganic films such as tungsten film and silicon oxide film, or a structure in which a resin film such as polyimide is formed on the substrate, can be used.

[0276] In other words, a light-emitting element can be formed on one substrate and then transferred to another substrate. Examples of substrates on which the light-emitting element is transferred, besides those mentioned above, include cellophane substrates, stone substrates, wood substrates, fabric substrates (including natural fibers (silk, cotton, linen), synthetic fibers (nylon, polyurethane, polyester), or recycled fibers (acetate fiber, cupro fiber, rayon, recycled polyester), leather substrates, and rubber substrates. By using these substrates, it is possible to manufacture light-emitting elements that are not easily damaged, have high heat resistance, are lightweight, or are thin.

[0277] Alternatively, a field-effect transistor (FET) can be formed on the aforementioned substrate, and a light-emitting element 150 can be fabricated on an electrode electrically connected to the FET. This allows for the fabrication of an active-matrix display device in which the driving of the light-emitting element is controlled by the FET.

[0278] The structure shown in this embodiment can be used in appropriate combinations with the structures shown in other embodiments.

[0279] Implementation Method 2 In this embodiment, an example of a method for synthesizing an organic compound for a light-emitting element applicable to one embodiment of the present invention is described, using organic compounds represented by general formulas (G1) and (G2) as examples.

[0280] <Synthetic methods for organic compounds represented by general formula (G1)> Organic compounds represented by the above general formula (G1) can be synthesized by various reaction synthesis methods. For example, they can be synthesized by the following synthetic schemes (S-1) and (S-2). By coupling compound 1, arylamine (compound 2), and arylamine (compound 3), a diamine compound (compound 4) is obtained.

[0281] Then, by coupling the diamine compound (compound 4), the halogenated aryl group (compound 5), and the halogenated aryl group (compound 6), an organic compound represented by the above general formula (G1) can be obtained.

[0282] [Chemical Formula 35]

[0283] [Chemical Formula 36]

[0284] Note that in the above synthetic schemes (S-1) and (S-2), A represents a substituted or unsubstituted fused aromatic ring or a substituted or unsubstituted fused heteroaromatic ring with 10 to 30 carbon atoms; Ar 1 to Ar 4 each independently represent a substituted or unsubstituted aromatic group with 6 to 13 carbon atoms; and X 1 to X 8 each independently represent any one of an alkyl group with 3 or more but less than 10 carbon atoms, a substituted or unsubstituted cycloalkyl group with 3 or more but less than 10 carbon atoms, or a trialkylsilyl group with 3 or more but less than 12 carbon atoms. Examples of such fused aromatic rings or fused heteroaromatic rings include phenanthrene, stilbene, acridinium, phenanthrene, and phenanthrene-thiazolinium. Particularly preferred are anthracene, pyrene, coumarin, quinacridone, perylene, fused tetraphenylene, and naphthobisbenzofuran.

[0285] Note that in the above synthetic schemes (S-1) and (S-2), when the Buchwald-Hartwig reaction is carried out using a palladium catalyst, X 10 to X 13 represent a halogen group or a trifluoromethanesulfonate group, and the halogen is preferably iodine, bromine, or chlorine. In the above reaction, palladium compounds such as bis(dibenzylacetone)palladium (0) and palladium acetate (II), ligands such as tris(tributyl)phosphine, tris(n-hexyl)phosphine, tricyclohexylphosphine, bis(1-adamantane)-n-butylphosphine, and 2-dicyclohexylphosphino-2',6'-dimethoxy-1,1'-biphenyl can be used. Additionally, in the above reaction, organic bases such as sodium terephthaloxide, and inorganic bases such as potassium carbonate, cesium carbonate, and sodium carbonate can be used. As solvents, toluene, xylene, mesitylene, benzene, tetrahydrofuran, dioxane, etc., can be used. Note that the reagents that can be used in the above reaction are not limited to the above-mentioned reagents.

[0286] The reactions carried out in the above synthetic schemes (S-1) and (S-2) are not limited to the Buchwald-Hartwig reaction, but can also utilize the Yuda-Kosugi-Stille coupling reaction using organotin compounds, the coupling reaction using Grinner reagents, the Ullmann reaction using copper or copper compounds, etc.

[0287] In the above synthetic scheme (S-1), when compounds 2 and 3 have different structures, it is preferable to react compound 1 with compound 2 to form a coupled body, and then react the resulting coupled body with compound 3. Note that when compound 1 reacts with compounds 2 and 3 one by one, compound 1 is preferably a dihalide, and X10 and X11 are preferably made using different halogens and selectively amination reactions are carried out one by one.

[0288] Furthermore, in the above synthetic scheme (S-2), when compounds 5 and 6 have different structures, it is preferable to react compounds 4 and 5 to form a coupler, and then react the resulting coupler with compound 6.

[0289] Implementation Method 3 In this embodiment, a light-emitting element having a structure different from that shown in Embodiment 1 will be described with reference to FIG6. Note that in FIG6, the same shading is used for parts having the same function as the element symbols shown in FIG1A, and sometimes the element symbols are omitted. Furthermore, parts having the same function as those in FIG1A are represented by the same element symbols, and sometimes their detailed descriptions are omitted.

[0290] <Example 2 of the structure of a light-emitting element> Figure 6 is a cross-sectional schematic diagram of the light-emitting element 250.

[0291] The light-emitting element 250 shown in Figure 6 has multiple light-emitting units (light-emitting unit 106 and light-emitting unit 108) between a pair of electrodes (electrode 101 and electrode 102). One of the multiple light-emitting units preferably has the same structure as the EL layer 100 shown in Figure 1A. That is, the light-emitting element 150 shown in Figure 1A preferably has one light-emitting unit, while the light-emitting element 250 preferably has multiple light-emitting units. Note that although the case where electrode 101 is the anode and electrode 102 is the cathode is described in the light-emitting element 250, the structure of the light-emitting element 250 can also be the opposite.

[0292] In the light-emitting element 250 shown in Figure 6, light-emitting units 106 and 108 are stacked, and a charge-generating layer 115 is disposed between the light-emitting units 106 and 108. Furthermore, the light-emitting units 106 and 108 may have the same structure or different structures. For example, the light-emitting unit 108 preferably adopts the same structure as the EL layer 100.

[0293] The light-emitting element 250 includes a light-emitting layer 120 and a light-emitting layer 170. The light-emitting unit 106, in addition to the light-emitting layer 120, also includes a hole injection layer 111, a hole transport layer 112, an electron transport layer 113, and an electron injection layer 114. The light-emitting unit 108, in addition to the light-emitting layer 170, also includes a hole injection layer 116, a hole transport layer 117, an electron transport layer 118, and an electron injection layer 119.

[0294] In the light-emitting element 250, any layer in the light-emitting unit 106 and light-emitting unit 108 may contain a compound according to an embodiment of the present invention. Note that light-emitting layer 120 or light-emitting layer 170 is preferred as the layer containing the compound.

[0295] The charge-generating layer 115 can have either a structure in which an acceptor substance as an electron acceptor is added to the hole-transporting material, or a structure in which a donor substance as an electron donor is added to the electron-transporting material. Alternatively, both structures can be stacked.

[0296] When the charge generation layer 115 comprises a composite material consisting of an organic compound and an acceptor substance, the same composite material used in the hole injection layer 111 shown in Embodiment 1 can be used as the composite material. Various compounds such as aromatic amine compounds, carbazole compounds, aromatic hydrocarbons, and polymers (oligomers, dendritic polymers, polymers, etc.) can be used as the organic compound. Furthermore, it is preferable to use a substance with a hole mobility of 1×10⁻⁶ cm² / Vs or higher as the organic compound. However, any other substance can be used as long as its hole transport capability is higher than its electron transport capability. Because the composite material consisting of the organic compound and the acceptor substance has good carrier injection and carrier transport capabilities, low-voltage driving and low-current driving can be achieved. Note that when the surface on the anode side of the light-emitting unit contacts the charge generation layer 115, the charge generation layer 115 can also function as a hole injection layer or a hole transport layer of the light-emitting unit; therefore, a hole injection layer or a hole transport layer may not be provided in this light-emitting unit. Alternatively, when the surface of the cathode side of the light-emitting unit is in contact with the charge generation layer 115, the charge generation layer 115 can also function as the electron injection layer or electron transport layer of the light-emitting unit. Therefore, the electron injection layer or electron transport layer may not be provided in the light-emitting unit.

[0297] Note that the charge-generating layer 115 can also be a laminated structure combining a layer of a composite material containing an organic compound and an acceptor substance with a layer made of other materials. For example, it can also be a structure combining a layer of a composite material containing an organic compound and an acceptor substance with a layer containing a compound selected from an electron-donating substance and a compound with high electron transport capacity. Alternatively, it can be a structure combining a layer of a composite material containing an organic compound and an acceptor substance with a layer containing a transparent conductive film.

[0298] The charge generation layer 115 sandwiched between the light-emitting unit 106 and the light-emitting unit 108 only needs to have a structure that injects electrons into one light-emitting unit and holes into the other light-emitting unit when a voltage is applied between the electrodes 101 and 102. For example, in FIG6, when a voltage is applied such that the potential of electrode 101 is higher than the potential of electrode 102, the charge generation layer 115 injects electrons into the light-emitting unit 106 and holes into the light-emitting unit 108.

[0299] From the viewpoint of light extraction efficiency, the charge generation layer 115 preferably has visible light transmittance (specifically, visible light transmittance of 40% or more). Furthermore, the charge generation layer 115 functions even if its conductivity is less than that of the pair of electrodes (electrode 101 and electrode 102).

[0300] By using the above-mentioned material to form the charge generation layer 115, the increase in driving voltage during the stacking of the light-emitting layer can be suppressed.

[0301] Although Figure 6 illustrates a light-emitting element with two light-emitting units, the same structure can be applied to light-emitting elements with three or more light-emitting units stacked together. As shown in light-emitting element 250, by arranging multiple light-emitting units between a pair of electrodes and separating them by a charge-generating layer, a light-emitting element that can achieve high brightness while maintaining low current density and has a longer lifespan can be realized. In addition, a low-power light-emitting element can also be realized.

[0302] Furthermore, in the above structures, the emission colors of the guest materials used in the light-emitting units 106 and 108 can be the same or different. When the light-emitting units 106 and 108 contain guest materials that emit light of the same color, the light-emitting element 250 becomes a light-emitting element that exhibits high luminous brightness with a lower current value, which is preferable. Conversely, when the light-emitting units 106 and 108 contain guest materials that emit light of different colors, the light-emitting element 250 emits light of multiple colors, which is also preferable. In this case, when multiple light-emitting materials with different emission wavelengths are used in one or both of the light-emitting layers 120 and 170, light with different emission peaks is synthesized, and therefore the emission spectrum of the light-emitting element 250 has at least two maxima.

[0303] The above structure is suitable for obtaining white light emission. By making the light emitted by the light-emitting layer 120 and the light-emitting layer 170 complementary colors, white light emission can be obtained. It is particularly preferable to select the object material in a way that achieves white light emission with high color rendering or at least has red, green, and blue light emission.

[0304] Preferably, the structure of the light-emitting layer 130 shown in Embodiment 1 is used in one or both of the light-emitting layers 120 and 170. By adopting this structure, a light-emitting element with good luminous efficiency and reliability can be obtained. The guest material included in the light-emitting layer 130 is a fluorescent material, a phosphorescent material, or a TADF material. Therefore, by using the structure of the light-emitting layer 130 shown in Embodiment 1 in one or both of the light-emitting layers 120 and 170, a light-emitting element with high efficiency, high reliability, and multi-color emission can be obtained.

[0305] Furthermore, in light-emitting elements with three or more stacked light-emitting units, the emission color of the object material used for each light-emitting unit can be the same or different. When the light-emitting element includes multiple light-emitting units that emit light of the same color, these units can achieve a high luminous brightness emission color with a lower current value than other colors. This structure is suitable for adjusting the emission color. It is particularly preferred for cases where object materials with different luminous efficiencies and exhibiting different emission colors are used. For example, when three light-emitting units are provided, by providing two light-emitting units containing a fluorescent material exhibiting the same emission color and one light-emitting unit containing a phosphorescent material exhibiting a different emission color from the fluorescent material, the luminous intensity of both fluorescence and phosphorescence can be adjusted. In other words, the intensity of the emission color can be adjusted according to the number of light-emitting units.

[0306] In the case of using the above-described light-emitting element comprising two fluorescent light-emitting units and one phosphorescent light-emitting unit, in order to efficiently obtain white light emission, it is preferable to adopt the following structure: the light-emitting element comprises two light-emitting units containing blue fluorescent material and one light-emitting unit containing yellow phosphorescent material; the light-emitting element comprises two light-emitting units containing blue fluorescent material and one light-emitting unit containing red phosphorescent material and green phosphorescent material; the light-emitting element comprises two light-emitting units containing blue fluorescent material and one light-emitting unit containing red phosphorescent material, yellow phosphorescent material and green phosphorescent material. Thus, the light-emitting element and phosphorescent light-emitting layer of one embodiment of the present invention can be appropriately combined.

[0307] Furthermore, at least one of the light-emitting layers 120 and 170 can be further divided into layers, with each layer containing a different light-emitting material. That is, at least one of the light-emitting layers 120 and 170 can also be formed from two or more layers. For example, when a light-emitting layer is formed by sequentially stacking a first light-emitting layer and a second light-emitting layer from the hole transport layer side, a material with hole transport properties can be used as the main material of the first light-emitting layer, and a material with electron transport properties can be used as the main material of the second light-emitting layer. In this case, the light-emitting materials contained in the first and second light-emitting layers can be the same or different materials. Additionally, the light-emitting materials contained in the first and second light-emitting layers can be materials that emit light of the same color or materials that emit light of different colors. By employing a structure with multiple light-emitting materials that emit light of different colors, it is also possible to obtain white light with high color rendering composed of three primary colors or four or more light-emitting colors.

[0308] This implementation method can be appropriately combined with other implementation methods.

[0309] Implementation Method 4 In this embodiment, a light-emitting device using the light-emitting element described in Embodiments 1 and 3 will be described with reference to FIGS. 7A and 7B.

[0310] Figure 7A is a top view showing the light-emitting device, and Figure 7B is a cross-sectional view cut along AB and CD in Figure 7A. The light-emitting device includes a driving circuit section (source-side driving circuit) 601, a pixel section 602, and a driving circuit section (gate-side driving circuit) 603, indicated by dashed lines, for controlling the light emission of the light-emitting element. Additionally, component symbol 604 is a sealing substrate, component symbol 625 is a desiccant, component symbol 605 is a sealant, and the inner side surrounded by the sealant 605 is a space 607.

[0311] Additionally, the guide wiring 608 is used to transmit signals input to the source-side drive circuit 601 and the gate-side drive circuit 603, and receives video signals, clock signals, start signals, reset signals, etc., from the FPC (Flexible Printed Circuit) 609, which serves as an external input terminal. Although only the FPC is shown here, it can also be equipped with a printed circuit board (PWB). The light-emitting device described in this specification includes not only the main body of the light-emitting device but also the light-emitting device with an FPC or PWB mounted on it.

[0312] Next, the cross-sectional structure of the light-emitting device described above will be described with reference to FIG7B. A driving circuit section and a pixel section are formed on the element substrate 610. Here, a pixel is shown as the source side driving circuit 601 of the driving circuit section and one pixel of the pixel section 602.

[0313] Additionally, a CMOS circuit combining an n-channel TFT 623 and a p-channel TFT 624 is formed in the source-side drive circuit 601. Furthermore, the drive circuit can also be formed using various CMOS circuits, PMOS circuits, or NMOS circuits. Although this embodiment shows an integrated driver with the drive circuit formed on the substrate, this structure is not mandatory; the drive circuit can also be formed externally instead of on the substrate.

[0314] Furthermore, the pixel portion 602 is formed of a pixel including a switching TFT 611, a current control TFT 612, and a first electrode 613 electrically connected to the drain of the current control TFT 612. Additionally, an insulator 614 is formed to cover the end of the first electrode 613. The insulator 614 can be formed using a positive photosensitive resin film.

[0315] Furthermore, to improve the coverage of the film formed on the insulator 614, the upper or lower end of the insulator 614 is formed as a curved surface. For example, when photosensitive acrylic resin is used as the material of the insulator 614, it is preferable that only the upper end of the insulator 614 has a curved surface. The radius of curvature of this curved surface is 0.2 μm or more and 0.3 μm or less. In addition, negative photosensitive materials or positive photosensitive materials can be used as the insulator 614.

[0316] An EL layer 616 and a second electrode 617 are formed on the first electrode 613. Here, the material of the first electrode 613, used as the anode, is preferably a material with a high work function. For example, in addition to single-layer films such as ITO films, indium tin oxide films containing silicon, indium oxide films containing 2 wt% to 20 wt% zinc oxide, titanium nitride films, chromium films, tungsten films, Zn films, and Pt films, multilayer films composed of titanium nitride films and films with aluminum as the main component, as well as three-layer multilayer films composed of titanium nitride films, films with aluminum as the main component, and titanium nitride films, can also be used. Note that when a multilayer structure is used, the wiring resistance is also low, good ohmic contact can be obtained, and it can be used as the anode.

[0317] In addition, the EL layer 616 is formed by various methods such as vapor deposition using a vapor deposition mask, inkjet printing, spin coating, etc. As the material constituting the EL layer 616, low molecular weight compounds or high molecular weight compounds (including oligomers and dendritic polymers) can also be used.

[0318] Furthermore, the material of the second electrode 617 formed on the EL layer 616 and used as the cathode is preferably a material with a low work function (Al, Mg, Li, Ca, or their alloys and compounds, MgAg, MgIn, AlLi, etc.). Note that when light generated in the EL layer 616 is transmitted through the second electrode 617, the second electrode 617 is preferably a stack composed of a metal thin film with reduced film thickness and a transparent conductive film (ITO, indium oxide containing 2 wt% to 20 wt% zinc oxide, indium tin oxide containing silicon, zinc oxide (ZnO), etc.).

[0319] Furthermore, the light-emitting element 618 is formed from a first electrode 613, an EL layer 616, and a second electrode 617. Preferably, the light-emitting element 618 has the structure shown in Embodiments 1 and 3. Additionally, the pixel portion includes multiple light-emitting elements, and the light-emitting device of this embodiment may also include both light-emitting elements having the structures described in Embodiments 1 and 3 and light-emitting elements having other structures.

[0320] Furthermore, by using a sealant 605 to bond the sealing substrate 604 and the component substrate 610 together, a light-emitting element 618 is disposed in the space 607 surrounded by the component substrate 610, the sealing substrate 604, and the sealant 605. In addition, the space 607 is filled with a filler, which may be inert gas (nitrogen, argon, etc.), or sometimes resin or a drying material, or both resin and a drying material.

[0321] As the sealant 605, epoxy resin or glass powder is preferably used. Furthermore, these materials are preferably those that minimize the permeability of moisture and oxygen. In addition to glass substrates and quartz substrates, plastic substrates made of FRP (fiber reinforced plastics), PVF (polyvinyl fluoride), polyester, or acrylic resin can also be used as the material for the sealing substrate 604.

[0322] The above method can be used to obtain a light-emitting device that uses the light-emitting element described in Embodiments 1 and 3.

[0323] <Example 1 of the structure of a light-emitting device> Figures 8A and 8B show an example of a light-emitting device having a light-emitting element that emits white light and a color layer (color filter) as an example of a display device.

[0324] Figure 8A shows a substrate 1001, a base insulating film 1002, a gate insulating film 1003, gate electrodes 1006, 1007, and 1008, a first interlayer insulating film 1020, a second interlayer insulating film 1021, a peripheral portion 1042, a pixel portion 1040, a driving circuit portion 1041, first electrodes of the light-emitting element 1024W, 1024R, 1024G, and 1024B, a separator wall 1025, an EL layer 1028, a second electrode of the light-emitting element 1029, a sealing substrate 1031, and a sealant 1032, etc.

[0325] Furthermore, in Figures 8A and 8B, color layers (red color layer 1034R, green color layer 1034G, and blue color layer 1034B) are disposed on the transparent substrate 1033. Additionally, a black layer (black matrix) 1035 may also be disposed. The transparent substrate 1033, on which the color and black layers are disposed, is aligned and fixed to the substrate 1001. Furthermore, the color and black layers are covered by a capping layer 1036. Additionally, Figure 8A shows a light-emitting layer where light does not pass through the color layers but is transmitted to the outside, and a light-emitting layer where light passes through each color layer but is transmitted to the outside. Light that does not pass through the color layers becomes white light, and light that passes through the color layers becomes red, blue, and green light, thus enabling the display of images using pixels of four colors.

[0326] Figure 8B shows an example in which a red color layer 1034R, a green color layer 1034G, and a blue color layer 1034B are formed between the gate insulating film 1003 and the first interlayer insulating film 1020. As shown in Figure 8B, the color layers can also be disposed between the substrate 1001 and the sealing substrate 1031.

[0327] In addition, although the light-emitting device described above adopts a structure that emits light from the side of the substrate 1001 on which the TFT is formed (bottom-emitting type), a light-emitting device that emits light from the side of the sealing substrate 1031 (top-emitting type) may also be adopted.

[0328] <Structural Example 2 of a Light-Emitting Device> Figures 9A and 9B show cross-sectional views of a top-emitting light-emitting device. In this case, a light-blocking substrate can be used for substrate 1001. The process up to fabricating the connecting electrode that connects the TFT and the anode of the light-emitting element is performed in the same way as for a bottom-emitting light-emitting device. Then, a third interlayer insulating film 1037 is formed to cover electrode 1022. This insulating film may also have a planarization function. The third interlayer insulating film 1037 can be formed using the same material as the second interlayer insulating film 1021 or various other materials.

[0329] Although the lower electrodes 1025W, 1025R, 1025G, and 1025B of the light-emitting element are all anodes here, they can also be cathodes. Furthermore, in the top-emitting type light-emitting device shown in Figures 9A and 9B, it is preferable that the lower electrodes 1025W, 1025R, 1025G, and 1025B are reflective electrodes. Additionally, it is preferable that the second electrode 1029 has the function of emitting light and allowing light to pass through. Furthermore, it is preferable that a microcavity structure is used between the second electrode 1029 and the lower electrodes 1025W, 1025R, 1025G, and 1025B to amplify light of a specific wavelength. The structure of the EL layer 1028 adopts the structure described in Embodiments 1 and 3, and employs an element structure capable of obtaining white light emission.

[0330] In Figures 8A and 8B, and Figures 9A and 9B, a structure for obtaining a white-emitting EL layer can be achieved by using multiple light-emitting layers or multiple light-emitting units. Note that the structure for obtaining white-emitting light is not limited to this.

[0331] When using the top-emitting structure shown in Figures 9A and 9B, sealing can be achieved using a sealing substrate 1031 with color layers (red color layer 1034R, green color layer 1034G, and blue color layer 1034B). A black layer (black matrix) 1030 located between pixels can be provided on the sealing substrate 1031. The color layers (red color layer 1034R, green color layer 1034G, and blue color layer 1034B) and the black layer (black matrix) can also be covered by a capping layer. Furthermore, a light-transmitting substrate is used as the sealing substrate 1031.

[0332] Furthermore, although Figure 9A shows a structure displaying full color using three colors: red, green, and blue, Figure 9B shows that a full-color display can also be achieved using four colors: red, green, blue, and white. Moreover, the structure for full-color display is not limited to these structures. For example, a full-color display can also be achieved using four colors: red, green, blue, and yellow.

[0333] According to one embodiment of the present invention, the light-emitting element uses fluorescent materials, phosphorescent materials, or TADF materials as the guest materials, thereby achieving high-efficiency multicolor light emission. Therefore, by using this light-emitting element in the light-emitting device shown in this embodiment, a light-emitting device with high luminous efficiency can be obtained.

[0334] The above method can be used to obtain a light-emitting device that uses the light-emitting element described in Embodiment 1 and Embodiment 3.

[0335] Furthermore, this embodiment can be appropriately combined with other embodiments.

[0336] Implementation Method 5 In this embodiment, an electronic device and a display device according to one embodiment of the present invention will be described.

[0337] According to one embodiment of the present invention, electronic devices and display devices that are planar, have high luminous efficiency, and are highly reliable can be manufactured. According to one embodiment of the present invention, electronic devices and display devices that are curved, have high luminous efficiency, and are highly reliable can be manufactured. Furthermore, as described above, light-emitting elements with high color reproduction can be obtained.

[0338] Examples of electronic devices include: televisions; desktop or laptop personal computers; monitors for computers, etc.; digital cameras; digital camcorders; digital photo frames; mobile phones; portable game consoles; portable information terminals; audio playback devices; pinball machines and other large-scale game machines, etc.

[0339] The portable information terminal 900 shown in Figures 10A and 10B includes a housing 901, a housing 902, a display unit 903, and a hinge unit 905, etc.

[0340] The outer casing 901 and outer casing 902 are connected together by a hinge 905. The portable information terminal 900 can be transformed from a folded state (Fig. 10A) to an unfolded state as shown in Fig. 10B. As a result, it has good portability when carried and high visibility when in use due to its large display area.

[0341] The portable information terminal 900 has a flexible display section 903 provided across the housing 901 and housing 902 connected by the hinge section 905.

[0342] The light-emitting device manufactured using one embodiment of the present invention can be used in the display unit 903. Therefore, a highly reliable portable information terminal can be manufactured.

[0343] The display unit 903 can display at least one of document information, still images, and moving images. When document information is displayed on the display unit 903, the portable information terminal 900 can be used as an e-book reader.

[0344] When the portable information terminal 900 is unfolded, the display unit 903 is maintained in a state with a large radius of curvature. For example, the display unit 903 can be maintained in a manner that includes a portion bent with a radius of curvature of 1 mm or more and 50 mm or less, preferably 5 mm or more and 30 mm or less. A portion of the display unit 903 is continuously arranged with pixels across the housing 901 and housing 902, thereby enabling curved surface display.

[0345] The display unit 903 is used as a touch panel, which can be operated with a finger or stylus.

[0346] The display unit 903 is preferably composed of a flexible display. This allows for continuous display across housings 901 and 902. Alternatively, housings 901 and 902 may each be equipped with a display.

[0347] To prevent the angle formed by the outer casing 901 and outer casing 902 from exceeding a predetermined angle when the portable information terminal 900 is unfolded, the hinge portion 905 preferably has a locking mechanism. For example, the locking angle (the angle at which further opening is prevented) is preferably 90° or higher and less than 180°, typically 90°, 120°, 135°, 150°, or 175°. This improves the convenience, security, and reliability of the portable information terminal 900.

[0348] When the hinge portion 905 has the aforementioned locking mechanism, excessive force can be suppressed from being applied to the display portion 903, thereby preventing damage to the display portion 903. This enables a highly reliable portable information terminal.

[0349] Housings 901 and 902 may also include a power button, operation button, external connection port, speaker, microphone, etc.

[0350] Either housing 901 or housing 902 may be equipped with a wireless communication module, which can transmit and receive data via computer networks such as the Internet, local area network (LAN), and Wi-Fi (registered trademark).

[0351] The portable information terminal 910 shown in Figure 10C includes a housing 911, a display unit 912, operation buttons 913, an external connection port 914, a speaker 915, a microphone 916, a camera 917, etc.

[0352] The light-emitting device manufactured using one embodiment of the present invention can be used in the display unit 912. Therefore, portable information terminals can be manufactured with high yield.

[0353] In the portable information terminal 910, a touch sensor is included in the display unit 912. By touching the display unit 912 with a finger or stylus, various operations such as making phone calls or inputting text can be performed.

[0354] Additionally, by operating button 913, the power can be switched on / off or the types of images displayed on display unit 912 can be changed. For example, the email composing screen can be switched to the main menu screen.

[0355] Furthermore, by incorporating a gyroscope sensor or accelerometer within the portable information terminal 910, the orientation (vertical or horizontal) of the portable information terminal 910 can be determined, and the screen display orientation of the display unit 912 can be automatically switched. Additionally, the screen display orientation can also be switched by touching the display unit 912, operating the operation button 913, or inputting sound using the microphone 916.

[0356] The portable information terminal 910 has one or more functions selected from telephones, laptops, and information reading devices. Specifically, the portable information terminal 910 can be used as a smartphone. The portable information terminal 910 can, for example, perform various applications such as mobile phone calls, email, article reading and editing, music playback, animation playback, internet communication, and computer games.

[0357] The camera 920 shown in Figure 10D includes a housing 921, a display unit 922, operation buttons 923, a shutter button 924, etc. Additionally, the camera 920 is equipped with a detachable lens 926.

[0358] The light-emitting device manufactured using one embodiment of the present invention can be used in the display unit 922. Therefore, a highly reliable camera can be manufactured.

[0359] Here, although the camera 920 has a structure that allows the lens 926 to be detached from the housing 921 and exchanged, the lens 926 and the housing 921 can also be formed as one unit.

[0360] By pressing the shutter button 924, the camera 920 can capture still or moving images. Additionally, the display unit 922 can be equipped with a touch panel, allowing users to take photos by touching the display unit 922.

[0361] In addition, the camera 920 may also have a separately mounted flash unit and viewfinder, etc. Furthermore, these components can also be assembled into the housing 921.

[0362] Figure 11A is a schematic diagram showing an example of a robotic vacuum cleaner.

[0363] The robotic vacuum cleaner 5100 includes a display 5101 on its top surface, multiple cameras 5102 on its sides, a brush 5103, and operation buttons 5104. Although not shown, the bottom of the robotic vacuum cleaner 5100 has tires and a suction port. Furthermore, the robotic vacuum cleaner 5100 includes various sensors such as infrared sensors, ultrasonic sensors, accelerometers, piezoelectric sensors, light sensors, and gyroscope sensors. Additionally, the robotic vacuum cleaner 5100 includes a wireless communication unit.

[0364] The 5100 robotic vacuum cleaner can walk automatically, and the 5120 can detect garbage and suck it up from the suction port on the bottom.

[0365] In addition, the robot vacuum cleaner 5100 analyzes the images captured by the camera 5102 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if it detects objects such as wiring that may get tangled in the brush 5103 through image analysis, it can stop the rotation of the brush 5103.

[0366] The display 5101 can show the remaining battery power and the amount of debris collected. Additionally, the display 5101 can show the robot vacuum's path. Furthermore, the display 5101 can be a touch panel, displaying the operation buttons 5104.

[0367] The robotic vacuum cleaner 5100 can communicate with portable electronic devices 5140 such as smartphones. Images captured by the camera 5102 can be displayed on the portable electronic device 5140. Therefore, the owner of the robotic vacuum cleaner 5100 can know the status of the room even when leaving home. Additionally, the content displayed on the monitor 5101 can be checked using the portable electronic device 5140 such as a smartphone.

[0368] The light-emitting device of one embodiment of the present invention can be used in a display 5101.

[0369] The robot 2100 shown in Figure 11B includes a computing unit 2110, an illuminance sensor 2101, a microphone 2102, an upper camera 2103, a speaker 2104, a display 2105, a lower camera 2106, an obstacle sensor 2107, and a movement mechanism 2108.

[0370] Microphone 2102 has the function of detecting the user's voice and ambient sounds. Additionally, speaker 2104 has the function of emitting sound. Robot 2100 can use microphone 2102 and speaker 2104 to communicate with the user.

[0371] The display 2105 has the function of displaying various information. The robot 2100 can display the information desired by the user on the display 2105. The display 2105 may be equipped with a touch panel. The display 2105 can be a detachable information terminal, which can be charged and send and receive data by setting it at a designated position on the robot 2100.

[0372] The upper camera 2103 and the lower camera 2106 are capable of capturing images of the robot 2100's surrounding environment. Additionally, the obstacle sensor 2107 can detect the presence or absence of obstacles in front of the robot 2100 when it moves using the mobility mechanism 2108. The robot 2100 can use the upper camera 2103, the lower camera 2106, and the obstacle sensor 2107 to perceive its surrounding environment and move safely.

[0373] The light-emitting device of one embodiment of the present invention can be used in a display 2105.

[0374] Figure 11C is a diagram showing an example of a goggle-type display. The goggle-type display includes, for example, a housing 5000, a display unit 5001, a speaker 5003, an LED light 5004, operation keys 5005 (including a power switch or operation switch), a connection terminal 5006, a sensor 5007 (which has the function of measuring factors such as force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, tilt, vibration, odor, or infrared radiation), a microphone 5008, a second display unit 5002, a support unit 5012, and headphones 5013, etc.

[0375] The light-emitting device of one embodiment of the present invention can be used in the display unit 5001 and the second display unit 5002.

[0376] Figures 12A and 12B illustrate a foldable portable information terminal 5150. The foldable portable information terminal 5150 includes a housing 5151, a display area 5152, and a bending portion 5153. Figure 12A shows the portable information terminal 5150 in its unfolded state. Figure 12B shows the portable information terminal 5150 in its folded state. Although the portable information terminal 5150 has a relatively large display area 5152, by folding the portable information terminal 5150, it becomes smaller and more portable.

[0377] The display area 5152 can be folded in half by the bending portion 5153. The bending portion 5153 is composed of a telescopic component and multiple support components. When folding, the telescopic component is stretched, and the bending portion 5153 is folded in such a way that it has a radius of curvature of 2 mm or more, preferably 5 mm or more.

[0378] Alternatively, the display area 5152 can also be a touch panel (input / output device) equipped with a touch sensor (input device). A light-emitting device according to one embodiment of the present invention can be used in the display area 5152.

[0379] This implementation method can be appropriately combined with other implementation methods.

[0380] Implementation Method 6 In this embodiment, examples of applying the light-emitting element of one embodiment of the present invention to various lighting devices will be described with reference to FIG13. By using the light-emitting element of one embodiment of the present invention, lighting devices with high luminous efficiency and reliability can be manufactured.

[0381] By forming a light-emitting element according to one embodiment of the present invention on a flexible substrate, it is possible to realize an electronic device or lighting device having a light-emitting area on a curved surface.

[0382] In addition, the light-emitting device that applies the light-emitting element of one embodiment of the present invention can also be used for automotive lighting, wherein the lighting is provided on the windshield, ceiling, etc.

[0383] Figure 13 shows an example of using a light-emitting element in an indoor lighting device 8501. Furthermore, because the light-emitting element can be made large-area, large-area lighting devices can also be formed. Additionally, a lighting device 8502 with a curved light-emitting area can be formed by using a curved housing. The light-emitting element shown in this embodiment is thin-film, so the housing design is highly flexible. Therefore, lighting devices that can accommodate various designs can be formed. Furthermore, a large lighting device 8503 can be installed on an indoor wall. Touch sensors can also be provided in lighting devices 8501, 8502, and 8503 to turn the power on or off.

[0384] Additionally, by using the light-emitting element on one side of the table surface, a lighting device 8504 that functions as a table can be provided. Furthermore, by using the light-emitting element as part of other furniture, a lighting device that functions as furniture can be provided.

[0385] As described above, by applying the light-emitting device according to one embodiment of the present invention, lighting equipment and electronic devices can be obtained. Note that the lighting equipment and electronic devices are not limited to those shown in this embodiment, and can be applied to lighting equipment and electronic devices in various fields.

[0386] The structure shown in this embodiment can be used in appropriate combinations with the structures shown in other embodiments. Example 1

[0387] In this embodiment, a light-emitting element according to one embodiment of the present invention and a comparative light-emitting element manufacturing example, as well as the characteristics of the light-emitting element, are described. The structure of the light-emitting element manufactured in this embodiment is the same as that in FIG1A. Tables 1 and 2 show the detailed contents of the element structure. The structure and abbreviation of the compounds used are shown below.

[0388] [Chemical Formula 37]

[0389] [Table 1] layer symbol film thickness (nm) Material weight ratio Light-emitting element 1 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: 2TMS-mmtBuDPhA2Anth:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.025:0.01 Electric hole transport layer 112 20 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Light-emitting element 2 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: 2TMS-mmtBuDPhA2Anth:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.05:0.01 Electric hole transport layer 112 20 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Light-emitting element 3 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: 2TMS-mmtBuDPhA2Anth:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.025:0.005 Electric hole transport layer 112 20 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO -

[0390] [Table 2] layer symbol film thickness (nm) Material weight ratio Light-emitting element 4 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: 2TMS-mmtBuDPhA2Anth:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.05:0.005 Electric hole transport layer 112 30 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Comparison of light-emitting element 5 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: 2TMS-mmtBuDPhA2Anth 0.8:0.2: 0.05 Electric hole transport layer 112 30 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO -

[0391] <Manufacturing of Light-Emitting Elements> The following illustrates a method for manufacturing the light-emitting element produced in this embodiment.

[0392] <<Manufacturing of Light-Emitting Element 1>> As electrode 101, an ITSO film with a thickness of 70 nm is formed on a glass substrate. The electrode area of ​​electrode 101 is 4 mm² (2 mm × 2 mm).

[0393] Next, as the hole injection layer 111, DBT3P-II and molybdenum oxide (MoO3) are co-deposited on electrode 101 in a weight ratio (DBT3P-II:MoO3) of 1:0.5 and a thickness of 40 nm.

[0394] Next, as the hole transport layer 112, PCCP is deposited on the hole injection layer 111 with a thickness of 20 nm.

[0395] Next, as the luminescent layer 130, 4,6mCzP2Pm, Ir(ppz)3, 2-trimethylsilyl-N,N,N',N'-tetratetra(3,5-di-tri-butylphenyl)-9,10-anthraphthalene (abbreviated as: 2TMS-mmtBuDPhA2Anth), and Ir(dmdppr-dmp)2(dpm) are co-deposited on the hole transport layer 112 in a weight ratio (4,6mCzP2Pm:Ir(ppz)3:2TMS-mmtBuDPhA2Anth:Ir(dmdppr-dmp)2(dpm)) of 0.8:0.2:0.025:0.01 and with a thickness of 40 nm. In the luminescent layer 130, 4,6mCzP2Pm and Ir(ppz)3 form an excited-state complex. In addition, 2TMS-mmtBuDPhA2Anth is a fluorescent material with a protective group, and Ir(dmdppr-dmp) 2(dpm) is a phosphorescent material containing Ir.

[0396] Next, as the electron transport layer 118, 4,6mCzP2Pm with a thickness of 20nm and NBPhen with a thickness of 10nm are sequentially deposited on the light-emitting layer 130. Next, as the electron injection layer 119, LiF with a thickness of 1nm is deposited on the electron transport layer 118.

[0397] Next, as electrode 102, an aluminum (Al) layer with a thickness of 200 nm is formed on the electron injection layer 119.

[0398] Next, in a nitrogen-atmospheric glove box, an organic EL sealant is used to fix a sealing glass substrate onto a glass substrate on which the organic material is formed, thereby sealing the light-emitting element 1. Specifically, the sealant is applied around the organic material formed on the glass substrate, the glass substrate and the sealing glass substrate are bonded together, and ultraviolet light with a wavelength of 365 nm is irradiated at 6 J / cm², followed by a heat treatment at 80°C for 1 hour. The light-emitting element 1 is obtained through the above process.

[0399] <<Manufacturing of Light-Emitting Elements 2 to 4 and Contrast Light-Emitting Element 5>> The only difference between light-emitting elements 2 to 4 and the comparative light-emitting element 5 and light-emitting element 1 is the structure of the light-emitting layer 130; the other processes are the same as those for light-emitting element 1. Detailed information about the element structures is described in Tables 1 and 2, therefore, detailed information about the manufacturing methods is omitted. In light-emitting elements 1 to 4, the materials used in the light-emitting layer 130 are the same, but their mixing ratios differ. Furthermore, the comparative light-emitting element 5 uses a fluorescent material with a protective base, 2TMS-mmtBuDPhA2Anth, but does not use the phosphorescent material Ir(dmdppr-dmp)2(dpm).

[0400] Characteristics of light-emitting elements Next, the characteristics of the light-emitting elements 1 to 4 and the comparative light-emitting element 5 were measured. For the measurement of luminance and CIE chromaticity, a colorimeter (BM-5A manufactured by Topcon Technohouse) was used. For the measurement of electroluminescence spectra, a multi-channel spectrometer (PMA-11 manufactured by Hamamatsu Photonics Co., Ltd., Japan) was used.

[0401] Figure 14 shows the external quantum efficiency-luminance characteristics of light-emitting elements 1 to 4 and the contrastive light-emitting element 5. Furthermore, Figure 15 shows the electroemission spectra of light-emitting elements 1 to 4 and the contrastive light-emitting element 5 when a current density of 2.5 mA / cm² is applied. Measurements of each light-emitting element were performed at room temperature (maintained in an atmosphere of 23°C). Figure 16 shows the absorption and emission spectra of a toluene solution of 2TMS-mmtBuDPhA2Anth used for light-emitting elements 1 to 4, the absorption spectrum of a dichloromethane solution of Ir(dmdppr-dmp)2(dpm), and the EL spectrum of the contrastive light-emitting element 9 (the EL spectrum of the excited-state complex formed by 4,6mCzP2Pm and Ir(ppz)3, described later).

[0402] The absorption spectra of the toluene solution of 2TMS-mmtBuDPhA2Anth and the dichloromethane solution of Ir(dmdppr-dmp)2(dpm) were measured using a UV-Vis spectrophotometer (V550 model, manufactured by Nippon Spectrophotometer Co., Ltd.). The absorption spectra shown in Figure 16 are obtained by subtracting the spectra measured with the solvent only in a quartz dish from the absorption spectra of the toluene solution of 2TMS-mmtBuDPhA2Anth and the dichloromethane solution of Ir(dmdppr-dmp)2(dpm). Emission spectra were measured using a fluorescence spectrophotometer (FS920, manufactured by Hamamatsu Photonics Co., Ltd., Nippon).

[0403] Table 3 shows the element characteristics of light-emitting elements 1 to 4 and comparative light-emitting element 5 at a range of 1000 cd / m².

[0404] [Table 3] Voltage (V) Current density (mA / cm 2) CIE Colorimeter (x, y) brightness (cd / m²) Current efficiency (cd / A) Power efficiency (lm / W) External quantum efficiency (%) Light-emitting element 1 3.30 1.88 (0.522, 0.460) 959 51.1 48.7 23.6 Light-emitting element 2 3.30 2.25 (0.499, 0.484) 1100 49.0 46.6 20.9 Light-emitting element 3 3.20 1.88 (0.446, 0.529) 1150 61.2 60.0 22.8 Light-emitting element 4 3.10 1.38 (0.439, 0.540) 839 60.6 61.5 21.7 contrast Light-emitting element 5 3.20 1.19 (0.323, 0.649) 1081 90.7 89.0 23.6

[0405] As shown in Figure 15, the emission spectra of light-emitting elements 1 to 4 have two peaks near 530 nm and 610 nm. The peak near 530 nm originates from 2TMS-mmtBuDPhA2Anth, and the peak near 610 nm originates from Ir(dmdppr-dmp)2(dpm). In other words, light-emitting elements 1 to 4 emit both light from 2TMS-mmtBuDPhA2Anth and light from Ir(dmdppr-dmp)2(dpm). On the other hand, the contrasting light-emitting element 5 emits green light with a peak wavelength of 534 nm and a half-width of 65 nm. Therefore, the contrasting light-emitting element 5 emits light from 2TMS-mmtBuDPhA2Anth.

[0406] In addition, as shown in FIG. 14, although the light-emitting elements 1 to 4 and the comparative light-emitting element 5 exhibit light emission from the fluorescent material, they have a high luminous efficiency, that is, an external quantum efficiency exceeding 20%. Here, the maximum generation probability of singlet excitons generated by the recombination of carriers (holes and electrons) injected from a pair of electrodes is 25%. Therefore, when the light extraction efficiency to the outside is 25%, the maximum external quantum efficiency of a normal fluorescent light-emitting element is 6.25%. In addition, for example, when the fluorescent material and the phosphorescent material emit light at a ratio of 1:1, the external quantum efficiency of the EL element is 15.5%. However, compared with the case where only singlet excitons contribute to light emission or the case where both normal fluorescent materials and phosphorescent materials contribute to light emission, the light-emitting elements 1 to 4 and the comparative light-emitting element 5 exhibit higher efficiency. This is because, in addition to the light emission from singlet excitons generated by the recombination of carriers (holes and electrons) injected from a pair of electrodes, light emission from the energy transfer of triplet excitons or light emission from singlet excitons generated from triplet excitons through reverse intersystem crossing in the exciplex is obtained. Therefore, it can be said that in a light-emitting element using a fluorescent material having a protecting group, the non-radiative deactivation of triplet excitons is suppressed, and both singlet excitation energy and triplet excitation energy are efficiently converted into light emission. That is, the light-emitting elements 1 to 4 and the comparative light-emitting element 5 can be regarded as light-emitting elements using ExEF.

[0407] In addition, as shown in FIGS. 14 and 15, the light-emitting elements 1 to 4, which include both a phosphorescent material and a fluorescent material as the light-emitting material, have the same efficiency as the comparative light-emitting element 5, which includes only a fluorescent material as the light-emitting material. That is, by using a fluorescent material having a protecting group on the luminescent body, even if both a phosphorescent material and a fluorescent material are used as the light-emitting material, a light-emitting element with high luminous efficiency can be manufactured. In addition, the comparative light-emitting element 5 can be regarded as a light-emitting element with a phosphorescent material concentration of 0. Therefore, by adjusting one or both of the concentration of the fluorescent material having a protecting group and the concentration of the phosphorescent material contributing to light emission, the emission color can be adjusted while maintaining high luminous efficiency. At this time, the concentration of the fluorescent material having a protecting group is preferably higher than the concentration of the phosphorescent material because the light emission of the fluorescent material and the light emission of the phosphorescent material can be obtained in a balanced manner.

[0408] <CV measurement results> Next, the electrochemical properties (oxidation reaction properties and reduction reaction properties) of 4,6mCzP2Pm and Ir(ppz)3 for the light-emitting layer used in each light-emitting element were measured using cyclic voltammetry (CV).

[0409] As the measuring instrument, an electrochemical analyzer (BAS Inc. ALS model 600A or 600C) was used. Furthermore, the solution used for the CV determination was modified as follows: as the solvent, dehydrated dimethylformamide (DMF) (manufactured by Aldrich Co., Ltd., 99.8%, catalog number: 22705-6) was used, and tetrabutylammonium perchlorate (n-Bu4NClO4) (manufactured by Tokyo Chemical Industry Co., Ltd., catalog number: T0836), used as the supporting electrolyte, was dissolved at a concentration of 100 mmol / L, and the analyte was dissolved at a concentration of 2 mmol / L. In addition, a platinum electrode (manufactured by BAS Inc., PTE platinum electrode) was used as the working electrode, a platinum electrode (manufactured by BAS Inc., Pt counter electrode for VC-3 (5cm)) was used as the auxiliary electrode, and an Ag / Ag+ electrode (manufactured by BAS Inc., RE7 non-aqueous solvent reference electrode) was used as the reference electrode. Measurements were performed at room temperature (20 to 25°C). The scan rate during CV measurements was uniformly set to 0.1 V / sec, and the oxidation potential Ea [V] and reduction potential Ec [V] relative to the reference electrode were measured. Ea is the intermediate potential between the oxidation-reduction phase, and Ec is the intermediate potential between the reduction-oxidation phase. Here, it is known that the potential energy of the reference electrode used in this embodiment relative to the vacuum level is -4.94 [eV]. Therefore, the HOMO level and LUMO level are obtained by using the formulas HOMO level [eV] = -4.94 - Ea and LUMO level [eV] = -4.94 - Ec, respectively.

[0410] According to CV measurements, the oxidation potential of 4,6mCzP2Pm is 0.95 V, and the reduction potential is -2.06 V. Furthermore, the HOMO level of 4,6mCzP2Pm calculated from CV measurements is -5.89 eV, and the LUMO level is -2.88 eV. Similarly, the oxidation potential of Ir(ppz)3 is 0.45 V, and the reduction potential is -3.17 V. Additionally, the HOMO level of Ir(ppz)3 calculated from CV measurements is -5.39 eV, and the LUMO level is -1.77 eV.

[0411] As mentioned above, the LUMO energy level of 4,6mCzP2Pm is lower than that of Ir(ppz)3, while the HOMO energy level of Ir(ppz)3 is higher than that of 4,6mCzP2Pm. Therefore, when this compound is used as a light-emitting layer, electrons and holes can be efficiently injected into 4,6mCzP2Pm and Ir(ppz)3, respectively, resulting in the formation of an excited-state complex between 4,6mCzP2Pm and Ir(ppz)3. Furthermore, as shown in Figure 16, the excited-state complex formed by 4,6mCzP2Pm and Ir(ppz)3 exhibits a emission peak near 530 nm.

[0412] As shown in Figure 16, the emission spectrum of the excited-state complex formed from 4,6mCzP2Pm and Ir(ppz)3 overlaps with both the absorption spectrum of 2TMS-mmtBuDPhA2Anth and the absorption spectrum of Ir(dmdppr-dmp)2(dpm). Therefore, the excitation energy of the excited-state complex can be efficiently transferred to both 2TMS-mmtBuDPhA2Anth and Ir(dmdppr-dmp)2(dpm). Furthermore, the emission spectrum of 2TMS-mmtBuDPhA2Anth overlaps with the absorption spectrum of Ir(dmdppr-dmp)2(dpm). Therefore, energy transfer from 2TMS-mmtBuDPhA2Anth to Ir(dmdppr-dmp)2(dpm) can also occur. Thus, by one embodiment of the present invention, a multicolor light-emitting element with excellent luminous efficiency can be manufactured. Example 2

[0413] In this embodiment, a light-emitting element according to an embodiment of the present invention different from the above embodiments is described, along with a manufacturing example of a comparative light-emitting element and its characteristics. The structure of the light-emitting element manufactured in this embodiment is the same as that shown in FIG. 1A. Tables 4 and 5 show the detailed structure of the element. The structures and abbreviations of the compounds used are shown below. For other organic compounds, please refer to the above embodiments and implementation methods.

[0414] [Compound 38]

[0415] [Table 4] layer symbol film thickness (nm) Material weight ratio Light-emitting element 4 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: 2TMS-mmtBuDPhA2Anth:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.05:0.005 Electric hole transport layer 112 30 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Light-emitting element 6 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: 2TMS-mmtBuDPhA2Anth:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.1:0.005 Electric hole transport layer 112 20 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO -

[0416] [Table 5] layer symbol Film thickness (nm) Material weight ratio Contrast light-emitting element 7 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: MeDPhA2A:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.05:0.005 Electric hole transport layer 112 30 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Contrast light-emitting element 8 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3: MeDPhA2A:Ir(dmdppr-dmp) 2(dpm) 0.8:0.2: 0.1:0.005 Electric hole transport layer 112 20 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Contrast light-emitting element 9 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :Ir(ppz) 3 0.8:0.2 Electric hole transport layer 112 20 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO -

[0417] <<Manufacturing of light-emitting element 4, light-emitting element 6, and contrast light-emitting elements 7 to 9>> The structure of the light-emitting element 4 is shown in Example 1 and Table 3. Similarly, the only difference between the manufacturing processes of the light-emitting element 6 and the comparative light-emitting elements 7 to 9 and those of the light-emitting element 1 is the manufacturing process of the light-emitting layer 130; the other processes are the same as those of the light-emitting element 1. Detailed information about the element structure is described in Table 3, therefore, detailed information about the manufacturing process is omitted. Comparative light-emitting elements 7 and 8 are light-emitting elements using MeDPhA2A fluorescent material without a protective substrate, while comparative light-emitting element 9 is a light-emitting element that does not contain fluorescent material.

[0418] Characteristics of light-emitting elements Next, the characteristics of the light-emitting elements 4, 6, and the comparative light-emitting elements 7 to 9 manufactured above were measured. The measurement method was the same as in Example 1.

[0419] Figure 17 shows the external quantum efficiency-luminance characteristics of light-emitting elements 4, 6, and contrast light-emitting elements 7 through 9. Figure 18 shows the electroluminescence spectra when a current flows through light-emitting elements 4, 6, and contrast light-emitting elements 7 through 9 at a current density of 2.5 mA / cm². Measurements of each light-emitting element were performed at room temperature (maintained in an atmosphere of 23°C).

[0420] Table 6 shows the element characteristics of light-emitting elements 4, 6, and contrasting light-emitting elements 7 to 9 near 1000 cd / m².

[0421] [Table 6] Voltage (V) Current density (mA / cm²) CIE Colorimeter (x, y) brightness (cd / m²) Current efficiency (cd / A) Power efficiency (lm / W) External quantum efficiency (%) Light-emitting element 4 3.10 1.38 (0.439, 0.540) 839 60.6 61.5 21.7 Light-emitting element 6 3.20 2.09 (0.426, 0.557) 1139 54.5 53.5 18.4 Contrast light-emitting element 7 3.40 2.68 (0.409, 0.569) 879 32.8 30.3 10.6 Contrast light-emitting element 8 3.50 3.76 (0.402, 0.580) 920 24.5 22.0 7.5 Contrast light-emitting element 9 3.30 1.63 (0.323, 0.610) 1053 64.7 61.6 19.0

[0422] As shown in Figure 18, the emission spectra of light-emitting elements 4 and 6 have two peaks near 530 nm and 610 nm. The peak near 530 nm originates from 2TMS-mmtBuDPhA2Anth, and the peak near 610 nm originates from Ir(dmdppr-dmp)2(dpm). In other words, light-emitting elements 4 and 6 emit both light from 2TMS-mmtBuDPhA2Anth and light from Ir(dmdppr-dmp)2(dpm). Similarly, the contrast light-emitting elements 7 and 8 also have two peaks near 530 nm and 610 nm. The peak near 530 nm originates from MeDPhA2A, and the peak near 610 nm originates from Ir(dmdppr-dmp)2(dpm). In other words, it can be seen that both light emission from MeDPhA2A and light emission from Ir(dmdppr-dmp)2(dpm) are obtained in the contrast light-emitting element 7 and contrast light-emitting element 8. Furthermore, green light emission with a peak wavelength of 531 nm and a half-width of 88 nm is obtained in the contrast light-emitting element 9. Therefore, it can be seen that light emission from the excited-state complex formed by 4,6mCzP2Pm and Ir(ppz)3 is obtained in the contrast light-emitting element 9.

[0423] Furthermore, as shown in Figure 17, although light-emitting elements 4 and 6 exhibit luminescence originating from fluorescent materials, they possess external quantum efficiencies equal to or higher than those of the comparative light-emitting element 9. On the other hand, comparative light-emitting elements 7 and 8 exhibit significantly lower external quantum efficiencies than comparative light-emitting element 9. Light-emitting elements 4, 6, 7, and 8 can be considered as elements with fluorescent and phosphorescent materials added to the comparative light-emitting element 9. That is, although light-emitting elements 4 and 6 have fluorescent materials added, they achieve multicolor luminescence while maintaining the same luminous efficiency as the comparative light-emitting element 9. On the other hand, in comparative light-emitting elements 7 and 8, the luminous efficiency decreases due to the addition of fluorescent and phosphorescent materials. Since light-emitting elements 4, 6, 7, and 8 use the same phosphorescent material, it can be said that the decrease in efficiency of comparative light-emitting elements 7 and 8 is due to the fluorescent material. It can be considered that the use of fluorescent materials without protecting groups leads to the deactivation of triple excitons. On the other hand, in the light-emitting element of one embodiment of the present invention, the non-radiative deactivation of triple excitons is suppressed, and they are efficiently converted into light emission. Thus, it can be seen that by using a fluorescent material with a protective group in the light-emitting layer, the energy transfer based on the Dexter mechanism from the host material and phosphorescent material to the fluorescent material and the non-radiative deactivation of the triple excitation energy can be suppressed.

[0424] Furthermore, the concentration of the fluorescent material with a protective group differs between light-emitting elements 4 and 6. Similarly, the concentration of the fluorescent material without a protective group differs between contrasting light-emitting elements 7 and 8. Here, according to Table 4, the reduction rate of external quantum efficiency between light-emitting elements 4 and 6 {(external quantum efficiency of light-emitting element 4 - external quantum efficiency of light-emitting element 6) / external quantum efficiency of light-emitting element 4 × 100} is approximately 15%, while the reduction rate of external quantum efficiency between contrasting light-emitting elements 7 and 8 {(external quantum efficiency of contrasting light-emitting element 7 - external quantum efficiency of contrasting light-emitting element 8) / external quantum efficiency of contrasting light-emitting element 7 × 100} is approximately 30%. Therefore, it can be seen that by using a fluorescent material with a protective group, the efficiency decrease caused by the increase in the concentration of the fluorescent material is suppressed.

[0425] <Brightness changes of light-emitting elements> Figure 19 shows the chromaticity-luminance characteristics of light-emitting elements 4 and 6. As can be seen from Figure 19, the chromaticity x and chromaticity y of light-emitting elements 4 and 6 remain almost unchanged with increasing luminance. In other words, light-emitting elements 4 and 6 are color-stable light-emitting elements with very little color change due to changes in luminance. This is because the fluorescent and phosphorescent materials in light-emitting elements 4 and 6 emit light through energy transfer from the excitation energy of the energy donor. Therefore, it can be seen that, through one embodiment of the present invention, a multi-color light-emitting element with minimal color change due to luminance can be manufactured.

[0426] Reliability Testing of Light-Emitting Elements Next, a constant current drive test of 2mA was performed on the light-emitting element 6, the contrast light-emitting element 5, and the contrast light-emitting element 9. Figure 20 shows the results. As can be seen from Figure 20, the contrast light-emitting element 5, which contains fluorescent materials, has a better drive life than the contrast light-emitting element 9, which does not contain fluorescent or phosphorescent materials. Furthermore, the drive life of the light-emitting element 6, which contains both fluorescent and phosphorescent materials, is even better. In other words, through one embodiment of the present invention, a light-emitting element exhibiting multicolor emission with high luminous efficiency and good reliability can be manufactured.

[0427] Next, Figure 21 shows the electroemission spectrum of the light-emitting element 6 after its brightness was reduced to 50% during the reliability test, and the electroemission spectrum of the light-emitting element 6 at 2.5 mA / cm² before the reliability test. The spectral intensities shown in Figure 21 were normalized for comparison of spectral shapes. As can be seen from Figure 21, the shape of the electroemission spectrum of the light-emitting element 6 remained almost unchanged before and after the reliability test. This is because the fluorescent and phosphorescent materials in the light-emitting element 6 emit light through energy transfer from the excitation energy of the energy donor. Therefore, it can be seen that, by one embodiment of the present invention, a multi-color light-emitting element with minimal color change before and after driving can be manufactured. Example 3

[0428] In this embodiment, a light-emitting element according to an embodiment of the present invention different from the above embodiments is described, along with a manufacturing example of a comparative light-emitting element and its characteristics. The structure of the light-emitting element manufactured in this embodiment is the same as that shown in FIG. 1A. Table 7 shows the detailed structure of the element. The structures and abbreviations of the compounds used are shown below. For other organic compounds, please refer to the above embodiments and implementation methods.

[0429] [Compound 39]

[0430] [Table 7] layer symbol film thickness (nm) Material weight ratio Light-emitting element 10 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm:3Cz2DPhCzBN:Oct-tBuDPQd:Ir(dmdppr-dmp) 2(dpm) 1:0.1: 0.025:0.005 Electric hole transport layer 112 20 mCzFLP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Contrast light-emitting element 11 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm:3Cz2DPhCzBN:Oct-tBuDPQd 1:0.1: 0.025 Electric hole transport layer 112 20 mCzFLP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO - Contrast light-emitting element 12 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 30 4,6mCzP2Pm :3Cz2DPhCzBN 1:0.1 Electric hole transport layer 112 20 PCCP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO -

[0431] Manufacturing of light-emitting element 10, contrast light-emitting element 11, and contrast light-emitting element 12 The only difference between the fabrication processes of light-emitting element 10, contrast light-emitting element 11, and contrast light-emitting element 12 and those of light-emitting element 1 is the fabrication process of hole transport layer 112 and light-emitting layer 130. The other fabrication processes are the same as those of light-emitting element 1. Detailed information about the element structure is described in Table 7, therefore, detailed information about the fabrication method is omitted. The light emission of light-emitting element 10 using 1,3,8,10-tetra-tertiary butyl-7,14-bis(3,5-di-tertiary butylphenyl)-5,12-dihydroquinolino[2,3-b]acridin-7,14-dione (abbreviated as Oct-tBuDPQd) fluorescent material with a protective group and Ir(dmdppr-dm)2(dpm) phosphorescent material will be explained in detail later.

[0432] Alternatively, the light-emitting element 10 can be considered as a light-emitting element in which phosphorescent material is added to the contrast light-emitting element 11. Furthermore, the contrast light-emitting element 11 can be considered as a light-emitting element in which fluorescent material with a protective group is added to the contrast light-emitting element 12. Therefore, the light-emitting element 10 can be considered as an element in which fluorescent material with a protective group and phosphorescent material are added to the contrast light-emitting element 12.

[0433] Characteristics of light-emitting elements Next, the characteristics of the light-emitting element 10, the contrast light-emitting element 11, and the contrast light-emitting element 12 manufactured above were measured. The measurement method was the same as in Example 1.

[0434] Figure 26 shows the external quantum efficiency-luminance characteristics of light-emitting element 10, contrast light-emitting element 11, and contrast light-emitting element 12. Figure 27 shows the electroluminescence spectra of light-emitting element 10, contrast light-emitting element 11, and contrast light-emitting element 12 when a current density of 2.5 mA / cm² is applied. Measurements of each light-emitting element were performed at room temperature (maintained in an atmosphere of 23°C).

[0435] Table 8 shows the element characteristics of light-emitting element 10, contrast light-emitting element 11, and contrast light-emitting element 12 near 1000 cd / m².

[0436] [Table 8] Voltage (V) Current density (mA / cm²) CIE Colorimeter (x, y) brightness (cd / m²) Current efficiency (cd / A) Power efficiency (lm / W) External quantum efficiency (%) Light-emitting element 10 4.80 1.97 (0.465, 0.495) 1071 54.5 35.7 21.9 Contrast light-emitting element 11 4.20 1.53 (0.275, 0.661) 1056 69.2 51.8 18.3 Contrast light-emitting element 12 3.50 2.20 (0.221, 0.507) 1027 46.8 42.0 16.8

[0437] As shown in Figure 27, the emission spectrum of light-emitting element 10 has two peaks near 526 nm and 608 nm. The peak near 526 nm originates from Oct-tBuDPQd, and the peak near 608 nm originates from Ir(dmdppr-dmp)2(dpm). In other words, it can be seen that light-emitting element 10 emits both light from Oct-tBuDPQd and light from Ir(dmdppr-dmp)2(dpm). Furthermore, the contrast light-emitting element 11 has a peak near 526 nm. This peak also originates from Oct-tBuDPQd. Additionally, the emission spectrum of contrast light-emitting element 12 has a peak near 506 nm, with a half-width of 81 nm. The light emitted by contrast light-emitting element 12 originates from 3Cz2DPhCzBN. Non-Patent Document 1 describes 3Cz2DPhCzBN as a TADF material.

[0438] Furthermore, as shown in FIG26, although the light-emitting element 10 exhibits light emission originating from the fluorescent material, it possesses an external quantum efficiency equal to or higher than that of the comparative light-emitting element 12. Moreover, the light-emitting element 10 has a higher external quantum efficiency than the comparative light-emitting element 11. Therefore, light emission from both the fluorescent and phosphorescent materials is obtained in the light-emitting element 10, and a higher luminous efficiency than that of both the comparative light-emitting elements 11 and 12 is achieved. As described above, this is because in the light-emitting element of one embodiment of the present invention, the non-radiative inactivation of triplet excitons is suppressed, and they are efficiently converted into light emission.

[0439] Furthermore, in the light-emitting element 10, TADF material is used as an energy donor. Therefore, TADF material is suitable for use in a light-emitting element according to one embodiment of the present invention. Additionally, in the light-emitting element 10, an organic compound containing a quinacridone skeleton in the light-emitting body is used as a fluorescent material having a protective group. Therefore, an organic compound containing a quinacridone skeleton is suitable for use in a light-emitting element according to one embodiment of the present invention. Example 4

[0440] In this embodiment, a light-emitting element according to an embodiment of the present invention different from the above embodiments is described, along with a manufacturing example of a comparative light-emitting element and its characteristics. The structure of the light-emitting element manufactured in this embodiment is the same as that shown in FIG. 1A. Table 7 shows the detailed structure of the element. The structures and abbreviations of the compounds used are shown below. For other organic compounds, please refer to the above embodiments and implementation methods.

[0441] [Compound 40]

[0442] [Table 9] layer symbol film thickness (nm) Material weight ratio Light-emitting element 13 electrode 102 200 Al - Electron injection layer 119 1 LiF - Electron transport layer 118(2) 10 NBPhen - 118(1) 20 4,6mCzP2Pm - Emissive layer 130 40 4,6mCzP2Pm :3Cz2DPhCzBN: Oct-tBuDPQd:TPA-DCPP 1:0.1: 0.025:0.005 Electric hole transport layer 112 20 mCzFLP - Hole Injection Layer 111 40 DBT3P-II: MoO 3 1:0.5 electrode 101 70 ITSO -

[0443] Manufacturing of Light-Emitting Element 13 The only difference between the manufacturing process of the light-emitting element 13 and that of the light-emitting element 10 is the manufacturing process of the light-emitting layer 130; the other processes are the same as those of the light-emitting element 10. Detailed information about the element structure is described in Table 9, therefore, detailed information about the manufacturing method is omitted.

[0444] Characteristics of light-emitting elements Next, the characteristics of the light-emitting element 13 manufactured above were measured. The measurement method was the same as in Example 1.

[0445] Figure 28 shows the external quantum efficiency-luminance characteristics of the light-emitting element 13. Furthermore, Figure 29 shows the electroluminescence spectrum when a current flows through the light-emitting element 13 at a current density of 2.5 mA / cm². Measurements of the light-emitting element were performed at room temperature (in an atmosphere maintained at 23°C).

[0446] In addition, Table 10 shows the element characteristics of the light-emitting element 13 near 3 cd / m².

[0447] [Table 10] Voltage (V) Current density (mA / cm²) CIE Colorimeter (x, y) brightness (cd / m²) Current efficiency (cd / A) Power efficiency (lm / W) External quantum efficiency (%) Light-emitting element 13 2.80 0.005 (0.464, 0.529) 3 53.8 60.4 17.2

[0448] As shown in Figure 29, the emission spectrum of the light-emitting element 13 has two peaks near 527 nm and 567 nm. The peak near 527 nm originates from Oct-tBuDPQd, and the peak near 567 nm originates from 7,10-bis(4-(diphenylamino)phenyl)-2,3-dicyanopyrazinephenanthrene (TPA-DCPP) of the TADF material. In other words, it can be seen that the light-emitting element 13 emits both light from Oct-tBuDPQd and light from TPA-DCPP. Non-Patent Literature 2 describes TPA-DCPP as a TADF material.

[0449] Furthermore, as shown in Figure 28, although the light-emitting element 13 exhibits light emission originating from the fluorescent material, it achieves a high external quantum efficiency exceeding the theoretical efficiency of a typical fluorescent element.

[0450] Reference Example 1 In this reference example, a method for synthesizing 2TMS-mmtBuDPhA2Anth (structural formula (229)) of the fluorescent material with a protective base used in Examples 1 and 2 is described.

[0451] <Step 1: Synthesis of 9,10-dibromo-2-trimethylsilylanthracene> 2.7 g (11 mmol) of 2-trimethylsilylanthracene was placed in a 500 mL three-necked flask, and the air in the flask was purged with nitrogen. 110 mL of N,N-dimethyl sulfoxide was added, and the mixture was stirred at room temperature. 4.0 g (23 mmol) of N-bromobutyldiamide was then added, and the mixture was stirred at room temperature for 15 hours. After stirring, water was added to the reaction mixture to obtain an aqueous layer and an organic layer. The aqueous layer was extracted with toluene, and the resulting extract and organic layer were combined. The mixture of extract and organic layer was washed with water and a saturated sodium thiosulfate aqueous solution, and then dried over magnesium sulfate. The mixture was separated by gravity filtration, and the filtrate was concentrated to give a yellowish-brown solid. After adding 450 mL of hexane and 50 mL of toluene to the obtained yellowish-brown solid, the mixture was filtered through a suction filter containing magnesium silicate (Wako Pure Chemical Industries, Ltd., catalog number: 066-05265), diatomaceous earth (Wako Pure Chemical Industries, Ltd., catalog number: 537-02305), and alumina to obtain a filtrate. The filtrate was concentrated to obtain a yellowish-brown solid. The solid was recrystallized from the filtrate using ethyl acetate / ethanol to give 2.4 g of a yellow solid in 54% yield. The synthetic scheme for step 1 is shown below (F-1).

[0452] [Chemical Formula 41]

[0453] Furthermore, the following shows the 1H NMR measurement results of the yellow solid obtained by step 1 above. Figures 22A, 22B, and 23 show the 1H NMR spectra. Figure 22B is a magnified view of Figure 22A in the range of 6.5 ppm to 9.0 ppm. Figure 23 is a magnified view of Figure 22A in the range of 0.0 ppm to 2.0 ppm. These results indicate the formation of 9,10-dibromo-2-trimethylsilylanthracene.

[0454] 1H NMR (CDCl 3,300MHz): σ=8.74(s,1H), 8.63-8.56(m,2H), 8.55(d,J=8.8Hz,1H), 7.75(d,J=8.3Hz,1H), 7.68-7.61(m,2H), 0.42(s,9H).

[0455] <Step 2: Synthesis of 2TMS-mmtBuDPhA2Anth> 1.4 g (3.3 mmol) of 9,10-dibromo-2-trimethylsilylanthracene, 2.6 g (6.6 mmol) of bis(3,5-tributylphenyl)amine, 1.3 g (14 mmol) of sodium tributyloxide, and 60 mg (0.15 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxy-1,1'-biphenyl (SPhos) were placed in a 200 mL three-necked flask, and the air in the flask was purged with nitrogen. 33 mL of xylene was added to the mixture, and the mixture was degassed under reduced pressure. 40 mg (70 μmol) of bis(dibenzylacetone)palladium(O) was added to the mixture, and the mixture was stirred at 150 °C for 6 hours under a nitrogen stream. After stirring, 400 mL of toluene was added to the resulting mixture, and the mixture was filtered through a suction filter containing magnesium silicate, diatomaceous earth, and alumina to obtain the filtrate. The filtrate was concentrated to obtain a brown solid. The solid was purified by silicone column chromatography (developing solvent: hexane:toluene = 9:1) to obtain a yellow solid. The yellow solid was recrystallized from the obtained yellow solid using ethyl acetate and ethanol, yielding 0.40 g of the target compound in a 12% yield. The synthetic scheme for step 2 is shown below (F-2).

[0456] [Chemical Formula 42]

[0457] The obtained yellow solid was purified by gradient sublimation. Sublimation purification was performed by heating the yellow solid at 260°C for 15 hours under a pressure of 3.5 Pa. After sublimation purification, 0.35 g of the target yellow solid was obtained in 87% yield.

[0458] Furthermore, the following shows the 1H NMR measurement results of the yellow solid obtained by step 2 above. Figures 24A, 24B, and 25 show the 1H NMR spectra. Figure 24B is a magnified view of the range of 6.5 ppm to 9.0 ppm in Figure 24A. Figure 25 is a magnified view of the range of 0.0 ppm to 2.0 ppm in Figure 24A. From these results, it can be seen that 2TMS-mmtBuDPhA2Anth is obtained.

[0459] 1H NMR(CDCl 3,300MHz): σ=8.25(s,1H), 8.24-8.21(m,1H), 8.15-8.11(m,2H), 7.40-7.37(m,1H), 7.30-7 .27(m,2H), 6.97-6.94(m,8H), 6.92-6.91(m,4H), 1.14(s,36H), 1.12(m,36H), 0.09(s,9H).

[0460] See Example 2 In this reference example, a method for synthesizing Oct-tBuDPQd (structural formula (104)) of the fluorescent material with a protective base used in Examples 3 and 4 is described.

[0461] <Step 1: Synthesis of 1,4-cyclohexadiene-1,4-dicarboxylic acid, 2,5-bis{(3,5-di-tri-butylphenyl)amino}-dimethyl ester> 5.6 g (24 mmol) of 1,4-cyclohexanedione-2,5-dicarboxylic acid dimethyl and 10 g (48 mmol) of 3,5-di-tert-butylaniline were placed in a 200 mL three-necked flask equipped with a reflux tube, and the mixture was stirred at 170 °C for 2 hours. Methanol was added to the resulting red-orange solid to slurry it, and the mixture was collected by suction filtration. The resulting solid was washed with hexane and methanol and dried to give 12 g of the target red-orange solid in 82% yield. The synthetic scheme for step 1 (E-1) is shown below.

[0462] [Chemical Formula 43]

[0463] The following shows the numerical data of the 1H NMR of the obtained solid. This indicates that the target compound has been obtained.

[0464] ¹H NMR (chloroform-d, 500 MHz): δ = 10.6 (s, 2H), 7.20 (t, J = 1.5 Hz, 2H), 6.94 (d, J = 2.0 Hz, 4H), 3.65 (s, 6H), 3.48 (s, 4H), 1.33 (s, 36H).

[0465] <Step 2: Synthesis of 1,4-benzenedicarboxylic acid, 2,5-bis{(3,5-di-tertiary-butylphenyl)amino}-dimethyl ester> 12 g (20 mmol) of 1,4-cyclohexadiene-1,4-dicarboxylic acid, 2,5-bis{(3,5-di-tri-butylphenyl)amino}-dimethyl ester, obtained in step 1, and 150 mL of toluene were placed in a 300 mL three-necked flask equipped with a reflux tube. The mixture was refluxed for 15 hours while air was bubbled into it. After stirring, the precipitated solid was collected by suction filtration. The solid was washed with hexane and methanol to give 7.3 g of the target compound as a red solid. The filtrate was concentrated to give another solid. This solid was washed with hexane and methanol and collected by suction filtration to give 3.1 g of the target compound as a red solid. Thus, a total of 10.4 g of the target compound was obtained in 85% yield. The synthetic scheme for step 2 (E-2) is shown below.

[0466] [Chemical Formula 44]

[0467] The following shows the numerical data of the 1H NMR of the obtained solid. This indicates that the target compound has been obtained.

[0468] ¹H NMR (chloroform-d, 500 MHz): δ = 8.84 (s, 2H), 8.18 (s, 2H), 7.08 (d, J = 2.0 Hz, 4H), 7.20 (t, J = 1.0 Hz, 2H), 3.83 (s, 6H), 1.34 (s, 36H).

[0469] <Step 3: Synthesis of 1,4-benzenedicarboxylic acid, 2,5-bis[N,N'-bis(3,5-di-tertiary butylphenyl)amino]-dimethyl ester> 4.0 g (6.7 mmol) of 1,4-benzenedicarboxylic acid, 2,5-bis{(3,5-di-tert-butylphenyl)amino}-dimethyl ester, 3.9 g (14.6 mmol) of 1-bromo-3,5-di-tert-butylbenzene, 0.46 g (7.3 mmol) of copper, 50 mg of copper iodide (0.26 mmol), 1.0 g (7.3 mmol) of potassium carbonate, and 10 mL of xylene obtained in step 2 were placed in a 200 mL three-necked flask equipped with a reflux tube. The mixture was degassed under reduced pressure, and the air in the system was then replaced with nitrogen. The mixture was refluxed for 20 hours. 0.46 g (7.3 mmol) of copper and 50 mg of copper iodide (0.26 mmol) were added to the resulting mixture, and reflux was carried out for another 16 hours. Dichloromethane was added to the resulting mixture to slurry it. Solids were removed by suction filtration, and the resulting filtrate was concentrated. The obtained solid was washed with hexane and ethanol. The solid was recrystallized from the solid using hexane / toluene to give 4.4 g of the target compound as a yellow solid in 72% yield. The synthetic scheme for step 3 is shown below (E-3).

[0470] [Chemical Formula 45]

[0471] The following shows the numerical data of the 1H NMR of the obtained solid. This indicates that the target compound has been obtained.

[0472] ¹H NMR (chloroform-d, 500 MHz): δ = 7.48 (s, 2H), 6.97 (t, J = 2.0 Hz, 4H), 7.08 (d, J = 1.5 Hz, 8H), 3.25 (s, 6H), 1.23 (s, 72H).

[0473] <Step 4: Synthesis of 1,3,8,10-tetra-tertiary butyl-7,14-bis(3,5-di-tertiary butylphenyl)-5,12-dihydroquinolino[2,3-b]acridin-7,14-dione (abbreviation: Oct-tBuDPQd)> 4.4 g (4.8 mmol) of 1,4-benzenedicarboxylic acid, 2,5-bis[N,N'-bis(3,5-di-tert-butylphenyl)amino]-dimethyl ester, and 20 mL of methanesulfonic acid obtained in step 3 were placed in a 100 mL three-necked flask equipped with a reflux tube, and the mixture was stirred at 160 °C for 7 hours. After cooling the mixture to room temperature, it was slowly added dropwise to 300 mL of ice water, and then left to stand until the temperature reached room temperature. The mixture was subjected to gravity filtration, and the resulting solid was washed with water and a saturated sodium bicarbonate aqueous solution. The solid was dissolved in toluene, and the resulting toluene solution was washed with water and a saturated brine solution, and dried with magnesium sulfate. The mixture was filtered using diatomaceous earth (Wako Pure Chemical Industries, Ltd., catalog number: 537-02305) and alumina. The filtrate was concentrated to give 3.3 g of a dark brown solid. The obtained solid was purified by silicone column chromatography (developing solvent: hexane: ethyl acetate = 20:1) to give 150 mg of the target compound as a red-orange solid in a 5% yield. The synthetic scheme for step 4 (E-4) is shown below.

[0474] [Chemical Formula 46]

[0475] Furthermore, the following shows the 1H NMR measurement results of the yellow solid obtained by step 4 above. Figures 30A, 30B, and 31 show the 1H NMR spectra. Figure 30B is a magnified view of Figure 30A in the range of 6.5 ppm to 9.0 ppm. Figure 31 is a magnified view of Figure 30A in the range of 0.5 ppm to 2.0 ppm. From these results, Oct-tBuDPQd can be obtained.

[0476] ¹H NMR (chloroform-d, 500 MHz): δ = 8.00 (s, 2H), 7.65 (t, J = 2.0 Hz, 2H), 7.39 (d, J = 1.0 Hz, 4H), 7.20 (d, J = 2.0 Hz, 2H), 6.50 (d, J = 1.0 Hz, 2H), 1.60 (s, 18H), 1.39 (s, 36H), 1.13 (s, 18H).

[0477] 100: EL layer 101: Electrode 102: Electrode 106: Light-emitting unit 108: Light-emitting unit 111: Hole Injection Layer 112: Hole Transport Layer 113: Electron Transport Layer 114: Electron Injection Layer 115: Charge Generation Layer 116: Hole Injection Layer 117: Electric Void Transport Layer 118: Electron Transport Layer 119: Electron Injection Layer 120: Emissive layer 130: Emissive layer 131: Compound 132: Compound 133: Compound 135: Compound 136: Compound 150: Light-emitting element 170: Emissive layer 250: Light-emitting element 301: Object Material 302: Object Material 310: Luminescent body 320: Protective base 330: Main materials 601: Source-side drive circuit 602: Pixel section 603: Gate-side drive circuit 604:Sealing substrate 605: Sealant 607: Space 608: Wiring 609:FPC 610: Component substrate 611: TFT for Switching 612: TFT for current control 613: Electrode 614: Insulators 616: EL layer 617: Electrode 618: Light-emitting element 623:n-channel TFT 624:p channel TFT 625: Desiccant 900: Portable Information Terminal 901: Outer shell 902: Outer shell 903: Display Unit 905: Hinge section 910: Portable Information Terminal 911: Outer shell 912: Display Unit 913: Operation Button 914: External connection port 915: Speaker 916: Microphone 917: Camera 920: Camera 921: Outer shell 922: Display Unit 923: Operation Button 924: Shutter Button 926: Lens 1001:Substrate 1002: Substrate insulating film 1003: Gate insulating film 1006: Gate electrode 1007: Gate electrode 1008: Gate electrode 1020: Interlayer insulating film 1021: Interlayer insulating film 1022: Electrode 1024B: Electrode 1024G: Electrode 1024R: Electrode 1024W: Electrode 1025B: Lower electrode 1025G: Lower electrode 1025R: Lower electrode 1025W: Lower electrode 1026: Partition Wall 1028: EL layer 1029: Electrode 1031:Sealing substrate 1032: Sealant 1033: Substrate 1034B: Color layer 1034G: Color Layer 1034R: Color layer 1035: Black layer 1036: Protective layer 1037: Interlayer insulating film 1040: Pixels 1041: Drive Circuit Section 1042: Surrounding Area 2100: Robot 2101: Illuminance Sensor 2102: Microphone 2103: Upper camera 2104: Speaker 2105: Monitor 2106: Lower camera 2107: Obstacle Sensor 2108: Mobile organization 2110: Computing device 5000: Casing 5001: Display Section 5002: Display Section 5003: Speaker 5004: LED lights 5005: Operation Key 5006: Connecting terminal 5007: Sensor 5008: Microphone 5012: Support section 5013: Headphones 5100: Robotic Vacuum Cleaner 5101: Monitor 5102: Camera 5103: Brush 5104: Operation button 5120: Garbage 5140: Portable electronic devices 5150: Portable Information Terminal 5151: Outer shell 5152: Display area 5153: Bending section 8501: Lighting equipment 8502: Lighting equipment 8503: Lighting equipment 8504: Lighting equipment

[0478]

Claims

1. A light-emitting element having a light-emitting layer between a pair of electrodes, wherein, The luminescent layer comprises a first material capable of converting triple excitation energy into luminescence, a second material capable of converting single excitation energy into luminescence, and a third material capable of converting triple excitation energy into luminescence. The first material comprises a first organic compound and a second organic compound. The first organic compound is a phosphorescent compound. The second material comprises a luminescent body and five or more protecting groups. The luminescent body is a fused aromatic ring or a fused heteroaromatic ring. Each of the five or more protecting groups independently comprises any one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 12 carbon atoms. Luminescence is obtained from both the second material and the third material.

2. A light-emitting element having a light-emitting layer between a pair of electrodes, wherein, The luminescent layer comprises a first material capable of converting triple excitation energy into luminescence, a second material capable of converting single excitation energy into luminescence, and a third material capable of converting triple excitation energy into luminescence. The first material comprises a first organic compound and a second organic compound, the first organic compound being a phosphorescent compound. The second material comprises a luminescent body and four protecting groups. The luminescent body is a fused aromatic ring or a fused heteroaromatic ring. The four protecting groups are not directly bonded to the fused aromatic ring or the fused heteroaromatic ring. Each of the four protecting groups independently comprises any one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 12 carbon atoms. Furthermore, luminescence is obtained from both the second material and the third material.

3. A light-emitting element having a light-emitting layer between a pair of electrodes, wherein, The luminescent layer comprises a first material capable of converting triple excitation energy into luminescence, a second material capable of converting single excitation energy into luminescence, and a third material capable of converting triple excitation energy into luminescence. The first material comprises a first organic compound and a second organic compound, the first organic compound being a phosphorescent compound. The second material comprises a luminescent body and two or more diarylamine groups. The luminescent body is a fused aromatic ring or a fused heteroaromatic ring, which is bonded to the two or more diarylamine groups. Each of the two or more diarylamine groups independently has at least one protecting group, which independently has one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 12 carbon atoms. Luminescence is obtained from both the second material and the third material.

4. A light-emitting element having a light-emitting layer between a pair of electrodes, wherein, The luminescent layer comprises a first material capable of converting triple excitation energy into luminescence, a second material capable of converting single excitation energy into luminescence, and a third material capable of converting triple excitation energy into luminescence. The first material comprises a first organic compound and a second organic compound, the first organic compound being a phosphorescent compound. The second material comprises a luminescent body and two or more diarylamine groups. The luminescent body is a fused aromatic ring or a fused heteroaromatic ring, which is bonded to the two or more diarylamine groups. Each of the two or more diarylamine groups independently has at least two protecting groups, each protecting group independently having one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 12 carbon atoms. Luminescence is obtained from both the second material and the third material.

5. The light-emitting element according to claim 3 or claim 4, wherein the diarylamine group is a diphenylamine group.

6. The light-emitting element according to any one of claims 1 to 4, wherein the alkyl group having 3 to 10 carbon atoms is a branched alkyl group.

7. The light-emitting element according to claim 6, wherein the branched alkyl group comprises quaternary carbon.

8. The light-emitting element according to any one of claims 1 to 4, wherein at least one of the atoms constituting the plurality of protecting groups is located directly on one face of the fused aromatic ring or the fused heteroaromatic ring, and at least one of the other atoms constituting the plurality of protecting groups is located directly on the other face of the fused aromatic ring or the fused heteroaromatic ring.

9. The light-emitting element according to any one of claims 1 to 4, wherein the first organic compound and the second organic compound are a combination forming an excited-state complex.

10. A light-emitting element according to any one of claims 1 to 4, wherein the fused aromatic ring or the fused heteroaromatic ring comprises any one of naphthalene, anthracene, fumonisin, styrene, triphenylene, tetraphenylene, pyrene, perylene, coumarin, quinacridone, and naphthobisbenzofuran.

11. A light-emitting element according to any one of claims 1 to 4, wherein the peak wavelength of the emission spectrum of the first material is located on the wavelength side shorter than the peak wavelength of the emission spectrum of the second material.

12. A light-emitting element according to any one of claims 1 to 4, wherein the emission spectrum of the first material overlaps with the absorption band of the absorption spectrum of the second material having the longest wavelength.

13. The light-emitting element according to any one of claims 1 to 4, wherein the third material is a phosphorescent compound.

14. The light-emitting element according to any one of claims 1 to 4, wherein the peak wavelength of the emission spectrum of the second material is located on the wavelength side shorter than the peak wavelength of the emission spectrum of the third material.

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