Organic light-emitting device

Abstract

To provide an organic compound that can be suitably used as a light-emitting material for displays, and an organic light-emitting device that includes such an organic compound.SOLUTION: A light-emitting layer includes a dopant compound and a host compound, and the host compound has a lone pair of electrons and a π electron orbital, and an energy difference ΔEST obtained by subtracting an energy level ET1 of the lowest triplet excited state T1 from an energy level ES1 of the lowest singlet excited state S1 is negative or is 0 eV≤ΔEST<0.0090 eV.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an organic light-emitting device that can be used as a light-emitting material.

Background Art

[0002] An organic light-emitting diode is an example of an organic light-emitting device that uses an organic electroluminescence (hereinafter referred to as organic EL) material composed of an organic compound. Even now, as displays and lighting devices equipped with organic light-emitting diodes are being provided on the market, there is a high need for new organic EL materials with higher luminous efficiency. Organic EL materials are an example of light-emitting materials. Organic EL materials include fluorescent materials and phosphorescent materials. The theoretical internal quantum efficiency of phosphorescent materials is four times higher than that of fluorescent materials. Therefore, research and development of phosphorescent materials has been ahead from the viewpoint of increasing the internal quantum efficiency.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, phosphorescent materials contain expensive metals such as iridium, so there is a problem of high cost.

[0006] 〔Regarding Patent Document 1 and Non-Patent Document 1〕 As a luminescent material with a lower cost than phosphorescent materials containing expensive metals such as iridium, the thermally activated delayed fluorescence materials described in Patent Document 1 and Non-Patent Document 1 are known. Hereinafter, the thermally activated delayed fluorescence material is referred to as a TADF (Thermally Activated Delayed Fluorescence) material.

[0007] The TADF material has an energy difference ΔE S1 obtained by subtracting the energy level E T1 of the lowest triplet excited state T1 from the energy level E ST of the lowest singlet excited state S1, which is configured to be small (for example, about 100 meV). The TADF material thermally induces reverse intersystem crossing from the lowest triplet excited state T1 to the lowest singlet excited state S1, and utilizes the lowest triplet excited state T1, which is originally deactivated as heat, as delayed fluorescence. As a result, in principle, the internal quantum efficiency of the organic EL material can be increased to 100%.

[0008] Also, by making ΔE ST as small as the energy at room temperature, reverse intersystem crossing is promoted, and the emission lifetime of the delayed fluorescence has been successfully shortened to several microseconds. This emission lifetime is comparable to that of conventional phosphorescent materials.

[0009] However, when assuming the use of TADF materials in displays, it has to be said that the emission lifetime of TADF materials is far from the practical level. The emission lifetime of TADF materials is about three orders of magnitude longer compared with the typical emission lifetime of organic EL materials used in displays provided in the market.

[0010] This long emission lifetime causes the degradation of TADF materials due to the increase in the triplet exciton density in TADF materials and the decrease in the emission efficiency during high-brightness emission.

[0011] 〔Regarding Non-Patent Document 2〕 Due to the exchange interaction in the excited state, the energy level E T1 of the lowest triplet excited state T1 is lower than the energy level E S1 of the lowest singlet excited state. In other words, ΔE ST becomes positive.

[0012] On the other hand, organic compounds have been reported in which the ΔE ST obtained by calculation is negative (see, for example, Non-Patent Document 2). The organic compound described in Non-Patent Document 2 has ΔE ST < -0.23 eV (see Table 3 of Non-Patent Document 2). Thus, ΔE ST that is negative and has a large absolute value belongs to a region called the Marcus inverted region. In organic EL materials belonging to the Marcus inverted region, it is considered that the rate constant of reverse intersystem crossing from the lowest triplet excited state T1 to the lowest singlet excited state S1 becomes small. In addition, the inventors of the present application have confirmed that such organic EL materials exhibit extremely low emission intensity and emission quantum yield experimentally. Therefore, it is not practical to use organic EL materials belonging to the region called the Marcus inverted region as light-emitting materials for displays.

[0013] One aspect of the present invention has been made in view of the above-described problems, and an object thereof is to provide an organic compound that can be suitably used as a light-emitting material for displays, and an organic light-emitting device including such an organic compound.

Means for Solving the Problems

[0014] To solve the above problems, an organic light-emitting device according to a first aspect of the present invention includes a light-emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the host compound is an organic compound having a lone pair and a π electron orbital, and the energy level E S1 from the lowest singlet excited state S1 to the energy level E T1 of the lowest triplet excited state T1, and the energy difference ΔE ST is negative or 0 eV ≦ ΔE ST < 0.0090 eV.

[0015] Further, an organic light-emitting device according to a second aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the first aspect described above, the host compound is a heptazine derivative having a lone pair and a π electron orbital, and is represented by the following formula (1) and has optional substituents R1, R2, R3.

Chemical formula

[0016] Further, an organic light-emitting device according to a third aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the first or second aspect described above, the radiative deactivation rate constant k r of the host compound is 1.0 × 10 6 s -1 < k r < 1.0 × 10

[0017] Further, an organic light-emitting device according to a fourth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the second aspect described above, the substituents R1, R2, R3 are composed of two types of substituents.

[0018] In addition, the organic light-emitting device according to the fifth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the second aspect described above, the substituents R1, R2, and R3 are each composed of three different types of substituents.

[0019] In addition, the organic light-emitting device according to the sixth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the second aspect described above, the substituents R1, R2, and R3 are each composed of one type of substituent.

[0020] In addition, the organic light-emitting device according to the seventh aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the fourth aspect described above, among the substituents R1, R2, and R3, the same substituent is used as the substituents R2 and R3, and the substituent R1 has a structure represented by the following formula (2): -S-R31, -O-R31, or -N-(R32)R33 ··· (2) Here, R31 to R33 are each independently a linear or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent, and each of the substituents R2 and R3 is a phenyl group or a phenyl group having 1 to 3 substituents.

[0021] In addition, the organic light-emitting device according to the eighth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the second aspect described above, the substituent R1 is any of the structures shown below,

Chemical formula

Chemical formula

Chemical formula

[0022] In addition, the organic light-emitting device according to the ninth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the sixth aspect described above, the substituents R1, R2, and R3 are any of the structures shown below.

Chemical formula

[0023] To solve the above problems, the organic light-emitting device according to the tenth aspect of the present invention includes a light-emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the dopant compound is an organic compound having a lone pair of electrons and a π electron orbital, and the energy difference ΔE S1 obtained by subtracting the energy level E T1 of the lowest triplet excited state T1 from the energy level E ST of the lowest singlet excited state S1 is a negative value or 0 eV ≦ ΔE ST < 0.0090 eV.

[0024] In addition, the organic light-emitting device according to the eleventh aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the tenth aspect described above, the dopant compound is a heptazine derivative having a lone pair of electrons and a π electron orbital, which is represented by the following formula (1) and has arbitrary substituents R1, R2, and R3.

Chemical formula

[0025] In addition, the organic light-emitting device according to the twelfth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the tenth or eleventh aspect described above, the radiative decay rate constant k r of the dopant compound is 1.0 × 10 6 s -1 < k r < 1.0 × 10

[0026] In addition, the organic light-emitting device according to the thirteenth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the eleventh aspect described above, the substituents R1, R2, and R3 are composed of two types of substituents.

[0027] In addition, in the organic light-emitting device according to the 14th aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the 11th aspect described above, the substituents R1, R2, and R3 are each composed of three different types of substituents.

[0028] In addition, in the organic light-emitting device according to the 15th aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the 11th aspect described above, the substituents R1, R2, and R3 are each composed of one type of substituent.

[0029] In addition, in the organic light-emitting device according to the 16th aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the 13th aspect described above, among the substituents R1, R2, and R3, the same substituent is used as the substituents R2 and R3, and the substituent R1 has a structure represented by the following formula (2): -S-R31, -O-R31, or -N-(R32)R33 ··· (2) Here, R31 to R33 are each independently a linear or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent, and each of the substituents R2 and R3 is a phenyl group or a phenyl group having 1 to 3 substituents.

[0030] In addition, in the organic light-emitting device according to the 17th aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the 11th aspect described above, the substituent R1 is any of the structures shown below,

Chemical formula

Chemical formula

Chemical formula

[0031] In addition, the organic light-emitting device according to the 18th aspect of the present invention has, in addition to the configuration of the organic light-emitting device according to the 15th aspect described above, the substituents R1, R2, and R3 being any of the structures shown below. [Chemical formula]

Effects of the Invention

[0032] According to one aspect of the present invention, an organic compound that can be suitably used as a light-emitting material for a display, and an organic light-emitting device including such an organic compound can be provided.

Brief Description of the Drawings

[0033]

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Mode for Carrying Out the Invention

[0034] 〔Organic Compound〕 <Overview> The organic compound according to one aspect of the present invention is an organic compound having a lone pair of electrons and a π electron orbital. Hereinafter, the organic compound according to one aspect of the present invention will be referred to as the organic compound of the present invention. The organic compound of the present invention can take at least a ground state S0, a lowest singlet excited state S1, and a lowest triplet excited state T1 (see FIG. 1). When electrons and holes are induced in the organic compound of the present invention, a part of them is excited to the lowest singlet excited state S1, and most of the rest is excited to the lowest triplet excited state T1. Hereinafter, the induced electrons and holes will be collectively referred to as carriers.

[0035] The organic compound of the present invention has an energy difference ΔE S1 obtained by subtracting the energy level E T1 of the lowest triplet excited state T1 from the energy level E ST of the lowest singlet excited state S1, and is configured such that -0.20 eV ≦ ΔE ST <0.0090 eV. In FIG. 1, the state where the energy level E T1 exceeds the energy level E S1 , that is, the state where the energy difference ΔE ST is Negative is shown.

[0036] Also, in the organic compound of the present invention, it is preferable that the energy difference ΔE ST is negative, that is, it is preferably configured such that -0.20 eV ≦ ΔE ST <0 eV.

[0037] In the organic compound of the present invention, the radiative deactivation rate constant k r is preferably 1.0×10 6 s -1 <k r .

[0038] In the organic compound of the present invention, the oscillator strength f is preferably 0.0050 < f

[0039] Note that each of the above-described energy difference ΔE ST , radiative deactivation rate constant k r , and oscillator strength f is described with two significant figures. When each of the energy difference ΔE ST , radiative deactivation rate constant k r , and oscillator strength f has three or more significant figures, the significant figures are made two by rounding the third significant figure.

[0040] <Advantages of the organic compound> The lowest triplet excited state T1 is an unstable excited state. Therefore, for example, when the organic compound of the present invention is used as a light-emitting material for a display including an organic light-emitting diode, the longer the time the excited carriers stay in the lowest triplet excited state T1, the more likely the organic compound will deteriorate, and the shorter the driving life, which is the life that can be driven as a light-emitting material, is likely to be.

[0041] In the organic compound of the present invention, since the energy difference ΔE ST is less than 0.0090 eV, intersystem crossing from the lowest triplet excited state T1 to the lowest singlet excited state S1 is easier compared to the TADF materials described in Patent Document 1 and Non-Patent Document 1. That is, the intersystem crossing rate constant k RISC of the organic compound of the present invention is larger than the rate constant k RISC of the TADF materials described in Patent Document 1 and Non-Patent Document 1. That is, the organic compound of the present invention can shorten the time that the excited carriers stay in the lowest triplet excited state T1 compared to the TADF materials described in Patent Document 1 and Non-Patent Document 1.

[0042] In addition, the luminescence lifetime of the fluorescence emission generated by the recombination of carriers in the lowest singlet excited state S1 is shorter than that of the fluorescence emission generated by the recombination of carriers from the lowest triplet excited state T1. Therefore, the organic compound of the present invention can shorten the luminescence lifetime compared to the TADF materials described in Patent Document 1 and Non-Patent Document 1.

[0043] The organic compound of the present invention configured as described above can enhance the durability compared to the TADF materials described in Patent Document 1 and Non-Patent Document 1, and consequently, can extend the driving lifetime of the organic light-emitting diode and the display using the organic compound of the present invention.

[0044] In addition, in the organic compound of the present invention, since the energy difference ΔE ST is -0.20 eV or more, compared with the organic compound described in Non-Patent Document 2, the rate constant k RISC can be increased, and the luminescence intensity and the luminescence quantum yield can be enhanced.

[0045] For an organic compound in which the energy difference ΔE ST is clearly less than -0.20 eV, since the energy difference ΔE ST is negative and its absolute value is too large, it belongs to the Marcus inverted region. It is predicted from the calculation results that the rate constant k RISC of an organic compound belonging to the Marcus inverted region is small. Also, it has been experimentally confirmed that the luminescence intensity and the luminescence quantum yield of an organic compound belonging to the Marcus inverted region are very low. Therefore, it is not practical to use an organic compound belonging to the Marcus inverted region as a luminescent material for displays.

[0046] Therefore, compared with the TADF materials described in Patent Document 1 and Non-Patent Document 1 and the organic compounds described in Non-Patent Document 2, the organic compounds of the present invention can be suitably used as light-emitting materials for displays provided with organic light-emitting diodes. The organic light-emitting diode is an aspect of an organic light-emitting device, and the organic light-emitting diode containing the organic compound of the present invention is included in the scope of the present invention.

[0047] <Energy difference ΔE ST Upper and lower limit values> (Energy difference ΔE ST Preferred lower limit value) When the reverse intersystem crossing in the organic compound is a non-adiabatic transition based on the weak spin-orbit interaction (H SO ) of the organic compound, the rate constant k RISC can be expressed by Equation (1) which is a Marcus theory-type formula (see Aizawa, N., Harabuchi, Y., Maeda, S., & Pu, Y.-J. Kinetic Prediction of Reverse Intersystem Crossing in Organic Donor-Acceptor Molecules. ChemRxiv. Preprint. https: / / doi.org / 10.26434 / chemrxiv.12203240.v1).

Equation

[0048] Here

Equation

[0049] From Equations (1) and (2), the rate constant k RISC is maximized when ΔE ST + λ = 0. The theoretical value of λ by TDDFT calculation is 0.050 eV or more and 0.20 eV or less in typical TADF materials (see Aizawa et al. mentioned above), and 0.0030 eV or more and 0.10 eV or less in the heptazine derivative which is an example of the organic compound of the present invention. The organic compound of the present invention has a lower limit value of the energy difference ΔE ST of -0.20 eV, whereby the rate constant k RISC can be increased.

[0050] In the organic compound according to one aspect of the present invention, the energy difference ΔE ST may be less than -0.20 eV.

[0051] (Upper limit value of energy difference ΔE ST ) The reorganization energy λ is always positive because it is based on the most stable energy of the lowest triplet excited state T1. So far, the smallest ΔE ST in isolated single organic molecules has been reported to be 0.009 eV (see Hironori Kaji et al. "Purely organic electroluminescent material realizing 100% conversion from electricity to light", Nat. Commun. 6, 8476 (2015)). The intermolecular exchange interaction is one of the origins of the energy difference ΔE ST . Note that the intermolecular exchange interaction is smaller than the intramolecular exchange interaction. The organic compound of the present invention has an upper limit value of the energy difference ΔE ST of 0.0090 eV, whereby the rate constant k RISC can be made larger than the TADF materials described in Patent Document 1 and Non-Patent Document 1.

[0052] <Lower limit value of the radiation inactivation rate constant k r > In the organic compound of the present invention, the radiation inactivation rate constant k r is 1.0×10 6 s -1 <k r ≦1×10 9 s -1 is preferably satisfied. According to this configuration, compared with typical light-emitting materials used in displays equipped with organic light-emitting diodes available on the market, quantum yields and emission lifetimes close to theirs, or quantum yields and emission lifetimes of the same degree, can be realized.

[0053] Further, in the organic compound of the present invention, it is preferable that the oscillator strength f satisfies 0.0050 < f. According to this configuration, the intensity of fluorescence can be increased. Therefore, when the organic compound of the present invention is used as a light-emitting material constituting the light-emitting layer of an organic light-emitting diode, the luminance of the organic EL element can be increased.

[0054] <Regarding the wavelength of fluorescence>

[0055] The wavelength λ (nm) of the fluorescence emitted by the organic compound of the present invention is determined according to the energy difference ΔE S1 from the energy level E of the lowest singlet excited state S1 S0 to the energy level E of the ground state S0 S01 (eV). The wavelength λ is obtained by λ = 1240 / ΔE S01 .

[0056] In the organic compound of the present invention, the wavelength λ is not particularly limited.

[0057] <Preferred examples of the organic compound> Hereinafter, a preferred example of the organic compound of the present invention will be described more specifically. However, for the organic compound of the present invention, the energy difference ΔE ST is negative or 0 eV ≦ ΔE STAs long as the relationship of <0.0090 eV is satisfied, its chemical structure is not limited to those exemplified below. Further, the organic compound of the present invention satisfies -0.20 eV ≤ ΔE ST is preferably satisfied with the relationship of <0.0090 eV.

[0058] In a preferred example, the organic compound of the present invention has a structure represented by the following formula (2).

Chemical formula

[0059] In formula (2), R1, R2, and R3 (hereinafter, may also be referred to as R1 to R3) are each independently an arbitrary substituent. X1, X2, X3, X4, X5, and X6 (hereinafter, may also be referred to as X1 to X6) are each independently a nitrogen atom or CH. When X1 to X6 are nitrogen atoms, a preferred example is a heptazine derivative.

[0060] In the above formula (2), it is preferable that at least one of X1 to X6 is a nitrogen atom, more preferably two or more or three or more are nitrogen atoms, and even more preferably all are nitrogen atoms. When all of X1 to X6 are nitrogen atoms, it has the structure of the following formula (1).

Chemical formula

[0061] In formula (1), the definitions of R1 to R3 are the same as those in the case of formula (2).

[0062] Hereinafter, a preferred example of R1 to R3 in formulas (1) and (2) will be described more specifically.

[0063] R1 to R3 may each be a different substituent, but in some cases, a structure in which two of R1 to R3 (for example, R2 and R3, or R1 and R3) are the same substituent and the other one is a different substituent is preferred. That is, in some cases, it is preferable that R1 to R3 are each composed of three different types of substituents, in some cases, it is preferable that they are composed of two types of substituents, and in some cases, it is preferable that they are composed of one type of substituent.

[0064] In particular, by making the symmetry in a preferred example lower than D 3h the energy difference ΔE ST is negative, that is, a relationship of -0.20 eV ≤ ΔE ST < 0 eV is satisfied, and in some cases, an organic compound having a high luminescence quantum yield can be realized.

[0065] (Regarding examples of R1 to R3) Examples of each of R1 to R3 are as follows.

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0066] (Regarding an example of R1) In a more preferred example, R1 has a structure represented by formula (3). -S-R31, -O-R31, or -N-(R32)R33 ··· (3) In formula (3), R31 to R33 are each independently a linear or cyclic hydrocarbon group having 20 or fewer carbon atoms, which may be substituted by a substituent. In one example, the linear or cyclic hydrocarbon group may preferably have 10 or fewer carbon atoms. Also, R32 and R33, which are bonded to the same nitrogen (N), may be bonded to each other to form a ring structure.

[0067] Specific examples of the linear or cyclic hydrocarbon group as R31 to R33 include, for example, a linear alkyl group, a linear alkenyl group, a linear alkynyl group, or a hydrocarbon ring group.

[0068] Examples of the linear alkyl group include linear or branched ones having 20 or fewer carbon atoms, preferably 15 or fewer carbon atoms, more preferably 10 or fewer carbon atoms, and even more preferably 5 or fewer carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a hexyl group, and an octyl group.

[0069] Examples of the linear alkenyl group include linear or branched ones having 20 or fewer carbon atoms, preferably 15 or fewer carbon atoms, and more preferably 10 or fewer carbon atoms, such as a vinyl group, a propenyl group, a butenyl group, a 2-methyl-1-propenyl group, a hexenyl group, and an octenyl group.

[0070] Examples of the linear alkynyl group include linear or branched ones having 20 or fewer carbon atoms, preferably 15 or fewer carbon atoms, and more preferably 10 or fewer carbon atoms, such as an ethynyl group, a propynyl group, a butynyl group, a 2-methyl-1-propynyl group, a hexynyl group, and an octynyl group.

[0071] Examples of hydrocarbon ring groups include cycloalkyl groups having 3 or more, preferably 5 or more, and 20 or less, preferably 15 or less, more preferably 10 or less carbon atoms, such as a cyclopropyl group, a cyclohexyl group, a tetradecahydroanthranyl group, etc.; cycloalkenyl groups having 3 or more, preferably 5 or more, and 20 or less, preferably 15 or less, more preferably 10 or less carbon atoms, such as a cyclohexenyl group, etc.; aryl groups having 6 or more and 18 or less, preferably 10 or less carbon atoms, such as a phenyl group, an anthranyl group, a phenanthryl group, a ferrocenyl group, etc.

[0072] These chain alkyl groups, chain alkenyl groups, chain alkynyl groups, or hydrocarbon ring groups exemplified as R31 to R33 may have substituents. Examples of substituents for the chain alkyl group, chain alkenyl group, or chain alkynyl group include halogen groups (halogen atoms) such as a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.

[0073] Examples of substituents for the hydrocarbon ring group include, in addition to the above halogen groups, an amino group (-NH2), a nitro group (-NO2), a cyano group (-CN), a hydroxyl group (-OH), an alkyl group, a halogenated alkyl group, an alkoxy group, etc. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, an octyloxy group, etc. The alkyl moiety of the alkyl group, halogenated alkyl group, alkoxy group, etc. preferably has 5 or less carbon atoms.

[0074] A more specific example of the structure represented by the above formula (3) is as follows.

Chemical formula

[0075] (Regarding an example of R2) In a more preferred example, R2 is selected from a hydrocarbon ring group or a heterocyclic group.

[0076] Examples of the hydrocarbon ring group include cycloalkyl groups having 3 or more, preferably 5 or more, and 20 or less, preferably 15 or less, more preferably 10 or less carbon atoms, such as a cyclopropyl group, a cyclohexyl group, a tetradecahydroanthranyl group, etc.; cycloalkenyl groups having 3 or more, preferably 5 or more, and 20 or less, preferably 15 or less, more preferably 10 or less carbon atoms, such as a cyclohexenyl group, etc.; aryl groups having 6 or more and 18 or less, preferably 10 or less carbon atoms, such as a phenyl group, an anthranyl group, a phenanthryl group, a ferrocenyl group, etc.

[0077] Examples of the heterocyclic group include a heteroaryl group composed of a 5- to 6-membered monocyclic ring or a condensed ring formed by condensation of 2 to 6 5- to 6-membered rings, and a heterocycloalkyl group composed of a 5- to 6-membered monocyclic ring or a condensed ring formed by condensation of 2 to 6 5- to 6-membered rings. Examples of the heteroatom include a nitrogen atom, an oxygen atom, a sulfur atom, etc. Specifically, a 5-membered monocyclic ring such as a thienyl group; a 6-membered monocyclic ring such as a pyridyl group, a 1-piperidinyl group, a 2-piperidinyl group, a 2-piperazinyl group, etc.; a condensed ring formed by condensation of 2 to 6 5- to 6-membered rings such as a benzothienyl group, a carbazolyl group, a quinolinyl group, an octahydroquinolinyl group, etc.

[0078] A more preferred example of R2 is a phenyl group which may have 1 to 5 substituents to be described later, or a pyridyl group which may have 1 to 4 substituents. When having substituents, the number thereof is not particularly limited, but may preferably be 1 to 3.

[0079] These hydrocarbon ring groups, heterocyclic groups, etc. may have substituents as described above. Examples of the substituents include halogen groups (halogen atoms) such as fluorine atom, chlorine atom, bromine atom, iodine atom; amino group (-NH2); nitro group (-NO2); cyano group (-CN); hydroxyl group (-OH); linear or branched alkyl groups having 20 or less carbon atoms, preferably 15 or less carbon atoms, more preferably 10 or less carbon atoms, still more preferably 5 or less carbon atoms, such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, hexyl group, octyl group; halogenated alkyl groups; alkoxy groups; etc. Examples of the alkoxy group include methoxy group, ethoxy group, propoxy group, isopropyl propoxy group, butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group, hexyloxy group, octyloxy group, etc. The alkyl moieties of the alkyl group, halogenated alkyl group, alkoxy group, etc. preferably have 5 or less carbon atoms.

[0080] Hereinafter, a phenyl group which may have 1 to 5 substituents or a pyridyl group which may have 1 to 4 substituents, which are preferred examples of R2, will be described in more detail. The substituents that the phenyl group or pyridyl group may have are preferably the above-mentioned halogen group, hydroxyl group, alkyl group, halogenated alkyl group, or alkoxy group. In the phenyl group which may have 1 to 5 substituents, the preferred number of substituents is 0, 1, 2, or 3. When the number of substituents is 1, it is preferable that the substituent is at the 2-position or 4-position of the phenyl group. When the number of substituents is 2, it is preferable that the substituents are at the 2,4-positions or 2,6-positions of the phenyl group. When the number of substituents is 3, it is preferable that the substituents are at the 2,4,6-positions of the phenyl group. When the number of substituents is 2 or 3, two or three substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen group may be preferable. In the pyridyl group which may have 1 to 4 substituents, the preferred number of substituents is 0, 1, 2, or 3, and in some cases, 0, 1, or 2 are more preferred.

[0081] A more specific example of R2 is as follows. [Chemical formula]

[0082] (Regarding an example of R3) In a more preferred example, R3 is selected from the substituents exemplified as R1 or the substituents exemplified as R2. R1 to R3 may be different substituents from each other, but it is more preferred that R3 and R1 are the same substituent, or that R3 and R2 are the same substituent.

[0083] (Regarding an example of a preferred combination of R1, R2, and R3) In an example of a preferred combination of R1, R2, and R3, R1 is a substituent that satisfies the above formula (3), and R2 and R3 are phenyl groups that may be substituted with 1 to 3 substituents. Here, more preferably, R2 and R3 are the same group. Even more preferably, R1 is any of the following, [Chemical formula] and R2 and R3 are a combination selected from an unsubstituted phenyl group and a phenyl group substituted with 1 to 3 methyl groups (preferably R2 and R3 are the same group).

[0084] As a particularly preferred example of the organic compound of the present invention, the following may be mentioned. [Chemical formula] [Chemical formula]

[0085] Among the above, 、2The organic compounds numbered the th, 3rd, 4th (11th), 6th, 16th, 23rd, 25th, 27th, 29th (33rd) may be more preferred.

[0086] <An example of a method for synthesizing an organic compound represented by formula (1) or formula (2)> The method for synthesizing the organic compound is not particularly limited. For example, a compound in which R1 to R3 in formula (1) or formula (2) are halogen groups (precursor compound) and a compound corresponding to R1, R2, and R3 can be synthesized by reacting in the presence of a Lewis acid catalyst (such as aluminum chloride, etc.). When using two or more compounds as the compounds corresponding to R1, R2, and R3, different R1, R2, and R3 can be introduced by appropriately adjusting the usage amounts of these compounds, the addition timing to the reaction system, and other reaction conditions. Details of the synthesis method can also be referred to in the examples section described later.

[0087] <Use, etc. of the organic compound of the present invention> The organic compound of the present invention can be suitably used, for example, as a light-emitting material for a light-emitting layer of an organic light-emitting element or an organic light-emitting device. The organic compound of the present invention may form a light-emitting layer with the compound alone, or may form a light-emitting layer as a composition (sometimes referred to as a "light-emitting composition") mixed with other compounds. An organic light-emitting element or an organic light-emitting device containing the organic compound of the present invention in the light-emitting layer also falls within the scope of the present invention.

[0088] In addition, the light-emitting layer often contains a host compound and a dopant compound. The dopant compound may also be called a guest compound. The host compound is responsible for charge (electron and hole) transport. The dopant compound is responsible for light emission. The organic compound of the present invention may be used as a host compound or a dopant compound in the light-emitting layer. In particular, among the organic compounds of the present invention, the energy difference ΔE ST is -0.20 eV ≤ ΔE STThose satisfying the relationship of <0.0090 eV can be used as either the host compound or the dopant compound. Among the organic compounds of the present invention, the energy difference ΔE ST is ΔE ST <-0.20 eV, and those satisfying this relationship are preferably used as the host compound.

[0089] In addition, the method used for fabricating the light-emitting layer is not limited. As the method for fabricating the light-emitting layer, for example, a vacuum evaporation method may be employed, or a coating method may be employed. Examples of the coating method include an inkjet method, a gravure printing method, and a nozzle coating method. Further, the substrate constituting the organic light-emitting device may be any substrate having translucency, and may be a hard substrate typified by glass or a flexible substrate typified by resin.

[0090] <Other embodiments> The present invention also includes the following embodiments.

[0091] The organic compound according to the first embodiment of the present invention is an organic compound having a lone pair of electrons and a π electron orbital, and the energy difference ΔE obtained by subtracting the energy level E of the lowest triplet excited state from the energy level E of the lowest singlet excited state S1 is -0.20 eV ≤ ΔE T1 <0.0090 eV. ST ST

[0092] In addition, the organic compound according to the second embodiment of the present invention, in addition to the configuration of the organic compound according to the first embodiment described above, has a radiative deactivation rate constant k r of 1.0×10 6 s -1 <k r r .

[0093] In addition, the organic compound according to the third embodiment of the present invention, in addition to the configuration of the organic compound according to the first or second embodiment described above, has an oscillator strength f of 0.0050 < f.

[0094] ​​Further, the organic compound according to the fourth aspect of the present invention is a heptazine derivative represented by the following formula (1) and having any three substituents R1, R2, and R3 independently of each other, in addition to the configuration of the organic compound according to any one of the above-described first to third aspects.

Chemical formula

[0095] Further, the organic compound according to the fifth aspect of the present invention employs a configuration in which, in addition to the configuration of the organic compound according to the fourth aspect described above, the substituents R1, R2, and R3 are composed of two types of substituents.

[0096] Further, the organic compound according to the sixth aspect of the present invention employs a configuration in which, in addition to the configuration of the organic compound according to the fourth aspect described above, the substituents R1, R2, and R3 are each composed of three different types of substituents.

[0097] Further, the organic compound according to the seventh aspect of the present invention employs a configuration in which, in addition to the configuration of the organic compound according to the fourth aspect described above, the substituents R1, R2, and R3 are composed of one type of substituent.

[0098] In order to solve the above problems, the organic compound according to the eighth aspect of the present invention is an organic compound having a lone pair of electrons and a π electron orbital, which is a heptazine derivative represented by the following formula (1) and having any three substituents R1, R2, and R3 independently of each other, and the substituents R1, R2, and R3 are composed of two or three types of substituents.

Chemical formula

[0099] Further, the organic light-emitting device according to the ninth aspect of the present invention includes the organic compound according to any one of the first to eighth aspects of the present invention.

[0100] In addition, the organic light-emitting device according to the tenth aspect of the present invention includes a light-emitting layer containing the organic compound that functions as a dopant compound and a host compound, in addition to the configuration of the organic light-emitting device according to the ninth aspect described above.

[0101] To solve the above problems, the organic light-emitting device according to the eleventh aspect of the present invention includes a light-emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the host compound is an organic compound having a lone pair and a π electron orbital, and the energy level E S1 from the lowest singlet excited state S1 to the energy level E T1 of the lowest triplet excited state T1, and the energy difference ΔE ST is negative or 0 eV ≦ ΔE ST < 0.0090 eV.

[0102] To solve the above problems, the organic light-emitting device according to the twelfth aspect of the present invention includes a light-emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the host compound is a heptazine derivative having a lone pair and a π electron orbital, which is represented by the following formula (1) and has an arbitrary substituent R1.

Chemical formula

Examples

[0103] 〔First Example〕 The organic compound A, which is the first example of the present invention, will be described below. The organic compound A is a heptazine derivative represented by the following formula (4). That is, the organic compound A has a heptazine as the parent nucleus, and the three substituents R1, R2, and R3 are such that R1 is a 1-piperidinyl group (that is, -N-(R32)R33 shown in formula (4), and -R32 and -R33 are bonded to each other to form a ring structure), and both R2 and R3 are 4-methoxyphenyl groups. That is, the three substituents are composed of two types of substituents.

Chem.

[0104] <Energy difference ΔE ST and calculation of oscillator strength f> (TDDFT calculation) Using TDDFT calculation, the structural optimizations of the lowest singlet excited state S1 and the lowest triplet excited state T1 of organic compound A were performed, and the energy difference ΔE ST and each of the oscillator strengths f of organic compound A were calculated. As the TDDFT calculation, the TDDFT calculation implemented in Gaussian16 was used, the functional ωB97X-D was used, and the basis function 6-31G(d) was used.

[0105] (ADC(2) calculation) In the most stable structure of the lowest triplet excited state T1 of organic compound A obtained by the above-mentioned TDDFT calculation, using the ADC(2) calculation, the energy difference ΔE ST and each of the oscillator strengths f of organic compound A were calculated. As the ADC(2) calculation, the ADC(2) calculation implemented in Q-Chem5.2 was used, and the basis function 6-31G(d) was used.

[0106] The energy difference ΔE ST and the oscillator strength f of organic compound A calculated by TDDFT calculation and ADC(2) calculation are shown in Table 1. The energy difference ΔE ST and the oscillator strength f calculated using the ADC(2) calculation that can consider two-electron excitation are, respectively, ΔE ST = -0.35 eV, and f = 0.017. That is, organic compound A was predicted to show a negative energy difference ΔE ST and a relatively large oscillator strength f.

Table 1

[0107] <Synthesis scheme> Organic compound A was obtained by the following synthetic scheme. That is, under an argon atmosphere, AlCl3 (1.83 mmol) was added to a dichloromethane solution (5 ml) of Anisole (2.5 mmol) at 0 °C. It was left at that temperature for 40 minutes, and trichloroheptadiene (0.83 mmol) was added at 0 °C. After 10 minutes, the temperature was raised to room temperature and rotated overnight. After 20 hours, reflux was started and continued for 4 hours. When the temperature was returned to room temperature, 0.5 ml (excess) of piperidine was added. After 1 hour, water was added to quench. The yellowish-white organic compound A was isolated by column purification (1% AcOEt / DCM → 15% AcOEt / DCM). In this example, the yield of organic compound A was 15%. [Chemical formula]

[0108] [Luminescence characteristics] Regarding the mixed thin film of the thus synthesized organic compound A and 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF), (1) the emission spectrum was measured using a fluorescence spectrophotometer Fluoromax-4 manufactured by HORIBA, (2) the emission quantum yield was measured using an integrating sphere C9920 manufactured by Hamamatsu Photonics, and (3) the emission lifetime τ of delayed fluorescence was measured using a Fluorolog-3 manufactured by HORIBA. In the mixed thin film of this example, the concentration of organic compound A was 5 wt%. Each of the upper, middle, and lower parts of Figure 2 shows the emission spectrum of the mixed thin film of this example, the temperature dependence of transient emission decay, and the rate constant k DF of the temperature dependence of delayed fluorescence, respectively, is a graph showing the temperature dependence.

[0109] The above measurements (1), (2), and (3) were carried out under an inert nitrogen atmosphere. Also, the measurement of (3) above was carried out while changing the temperature using a cryostat CoolSpeK manufactured by UNISOKU. The temperature dependence of the obtained emission lifetime τ was analyzed by mathematical formula (3) assuming the thermal equilibrium between the lowest singlet excited state S1 and the lowest triplet excited state T1, and the energy difference ΔE STand the radiative deactivation rate constant k r The experimental values of were estimated. In Equation (3), k B is the Boltzmann constant, T is the absolute temperature, and k DF is the rate constant of delayed fluorescence.

Number

[0110] The mixed thin film of this example exhibited blue emission (CIE 0.16, 0.14) with a maximum emission wavelength of 442 nm (see the upper part of Figure 2). In addition, the mixed thin film of this example had a high emission quantum yield of 85%, a short emission lifetime τ of 1066 ns, and a radiative deactivation rate constant k r 1.2×10 8 s -1 The energy difference ΔE ST was estimated to be ΔE ST =0.004 eV from the temperature dependence of the emission lifetime τ (see the middle and lower parts of Figure 2). Further, the oscillator strength f without considering the degeneracy estimated from the radiative deactivation rate constant k r using Equation (4) was f = 0.35.

Number

Number

[0111] 〔First Reference Example〕 A toluene solution of the organic compound A synthesized using the synthesis scheme described in the first example is taken as the first reference example. In the toluene solution of this reference example, the concentration of the organic compound A is 8×10 -5It is M. For the toluene solution of this reference example, similar to the first embodiment, (1) the emission spectrum was measured using a fluorescence spectrophotometer Fluoromax-4 manufactured by HORIBA, (2) the emission quantum yield was measured using an integrating sphere C9920 manufactured by Hamamatsu Photonics, and (3) the emission lifetime τ of the delayed fluorescence was measured using a Fluorolog-3 manufactured by HORIBA. Each of the upper, middle, and lower parts of Fig. 3 shows the emission spectrum of the toluene solution of this reference example, the temperature dependence of the transient emission decay, and the rate constant k of the delayed fluorescence DF is a graph showing the temperature dependence.

[0112] The toluene solution of this reference example showed blue emission (CIE 0.16, 0.16) with a maximum emission wavelength of 442 nm (see the upper part of Fig. 3). Also, the toluene solution of this reference example showed a high emission quantum yield of 75% and a short emission lifetime τ of 588 ns. From the temperature dependence of the emission lifetime τ, the energy difference ΔE ST was estimated to be ΔE ST = 0.033 eV, and the radiative deactivation rate constant k r was estimated to be k r = 2.2×10 7 s -1 (see the middle and lower parts of Fig. 3).

[0113] 〔Second Embodiment Group〕 Organic compounds 1 to 38, which are the second embodiment group of the present invention, will be described below. Each of organic compounds 1 to 38 is 38 organic compounds described above as particularly preferred examples of the organic compounds of the present invention.

[0114] Similar to the first embodiment, using TDDFT calculation, the structural optimization of the lowest singlet excited state S1 and the lowest triplet excited state T1 of organic compounds 1 to 38 was performed, and the energy difference ΔE ST and the oscillator strength f of organic compounds 1 to 38 were calculated respectively. Fig. 4 is a graph showing the correlation between the energy difference ΔE ST and the oscillator strength f in organic compounds 1 to 38. The solid line shown in Fig. 4 is the function f (ΔEST) = (ΔE ST - 0.18) × 0.3 (ΔEST)represents. That is, each of the organic compounds 1 to 38 satisfies the relational expression of f ≧ (ΔE ST −0.18) × 0.3.

[0115] The energy difference ΔE ST of the organic compound A, which is the first embodiment, when calculated using TDDFT, ΔE ST = 0.27 eV, but when calculated from the luminescence characteristics of the synthesized organic compound A, ΔE ST = 0.0040 eV. That is, the energy difference ΔE ST calculated from the luminescence characteristics shifts in a direction to be smaller compared to the energy difference ΔE ST when using TDDFT calculation.

[0116] Based on the results of the first embodiment described above, in the space spanned by the energy difference ΔE ST and the oscillator strength f, the energy difference ΔE ST and the oscillator strength f obtained using TDDFT calculation, and each of the organic compounds 1 to 38 that satisfies the relational expression of f ≧ (ΔE ST −0.18) × 0.3 is included in the scope of the present invention.

[0117] [First Comparative Example] The organic compound B described in Non-Patent Document 2 will be described below. The organic compound B is a heptazine derivative represented by the following formula (5). That is, the organic compound B has a heptazine as the parent nucleus, and the three substituents R1, R2, and R3 are all 4-methoxyphenyl groups. [Chemical formula]

[0118] Regarding the organic compound B, the energy difference ΔE ST and the oscillator strength f calculated using ADC(2) calculation were ΔE ST = −0.250 eV and f = 0.0000050, respectively.

[0119] On the other hand, for the organic compound B, a toluene solution was prepared, and in the same manner as in the first embodiment, (1) the emission spectrum was measured using a fluorescence spectrophotometer Fluoromax-4 manufactured by HORIBA, (2) the emission quantum yield was measured using an integrating sphere C9920 manufactured by Hamamatsu Photonics, and (3) the emission lifetime τ was measured using a Fluorolog-3 manufactured by HORIBA. As a result, the radiative deactivation rate constant k r , and the oscillator strength f were k r = 1.0×10 6 s -1 , and f = 0.0039, respectively. It was found that the organic compound B did not exhibit delayed fluorescence. Therefore, for the organic compound B, the energy difference ΔE ST could not be evaluated.

[0120] As described above, since the organic compound B does not exhibit delayed fluorescence and the energy difference ΔE ST cannot be evaluated, it is not included in the scope of the present invention. The organic compound B has a low fluorescence intensity due to an extremely small oscillator strength. Therefore, it is difficult to use the organic compound B as a light-emitting material for displays.

[0121] 〔Third Example Group〕 The organic compound pX-Y, which is the third example group of the present invention, will be described below.

[0122] <Nomenclature Rules for Organic Compounds> In the organic compound pX-Y, each of X and Y is an integer of 1 or more and 186 or less, and corresponds to the numbers of the 186 types of substituents exemplified in the section of (Examples of R1 to R3). The organic compound pX-Y adopts a substituent specified by X common to R2 and R3 and a substituent specified by Y as R1 in the structure of the following formula (1).

Chemical Formula

[0123] For example, the organic compound p37-151 is represented by the following formula (6).

Chem.

[0124] <Screening Calculation> In the organic compound pX-Y, R2 and R3 are selected from the substituents of 186. Similarly, R1 is selected from the substituents of 186. Therefore, the organic compound pX-Y is a group of 34,596 organic compounds.

[0125] For these 34,596 organic compounds pX-Y, the structural optimization of T1 was performed by Unrestricted DFT implemented in Gaussian16. The LC-BLYP was used for the functional, and 0.18 Bohr was used for the region division parameter -1 , and 6-31G was used for the basis function. Using the obtained T1 optimized structure, the energy difference ΔE ST and the oscillator strength f were calculated by TDDFT calculation. The LC-BLYP was used for the functional, and 0.18 Bohr was used for the region division parameter -1 , and 6-31G(d) was used for the basis function. Hereinafter, this calculation is referred to as the screening calculation.

[0126] The results of the screening calculation for 34,596 organic compounds pX-Y are shown in Fig. 5. Fig. 5 is a scatter plot showing the phase space of the energy difference ΔE ST and the oscillator strength f in 34,596 organic compounds pX-Y. Among the 34,596 organic compounds pX-Y, 10,006 organic compounds pX-Y selected in ascending order of the energy difference ΔE ST are shown in Figs. 6 to 56. Figs. 6 to 56 are tables showing the energy difference ΔE ST and the oscillator strength f of 10,006 organic compounds pX-Y. The numbers shown in Figs. 6 to 56 are arranged in ascending order of the energy difference ΔE ST .

[0127] <High-Precision Calculation> Furthermore, for organic compounds C, D, and E among the organic compounds pX-Y, the structure optimization of T1 was performed using Unrestricted MP2 implemented in Gaussian16. The cc-pVDZ basis function was used. Using the obtained T1 optimized structure, the energy difference ΔE ST and oscillator strength f were calculated using EOM-CCSD or ADC(2). The cc-pVDZ basis function was used. Hereinafter, this calculation is referred to as high-precision calculation.

[0128] In the above-described screening calculation, organic compounds C and D showed a relatively small energy difference ΔE ST and a large oscillator strength f. Organic compound E is an analog of organic compounds C and D.

[0129] Organic compound C is organic compound p37-151 and is represented by the following formula (7).

Chemical formula

Chemical formula

[0130] The synthesis of intermediate I1 was carried out as follows. 2,2,2-Trifluoroethanol (199 mL, 2.78 mmol) was dissolved in tetrahydrofuran (10 mL), and sodium hydride (121 mg, 3.0 mmol) was added at 0 °C. After stirring for 30 minutes, a solution of cyanuric acid (700 mg, 2.53 mmol) in tetrahydrofuran (20 mL) was slowly added dropwise at 0 °C, and the mixture was stirred at 0 °C for 2 hours and then at room temperature for 1 hour. The reaction solution was concentrated under reduced pressure to obtain intermediate I1.

[0131] Organic compound D is organic compound p37-107 and is represented by the following formula (9).

Chemical formula

Chemical formula

[0132] The synthesis of intermediate I2 was carried out as follows. Cyanuric acid chloride (677 mg, 2.45 mmol) was dissolved in tetrahydrofuran (20 mL), and piperidine (266 mL, 2.7 mmol) was added at room temperature. After 30 minutes, the temperature was raised to 50 °C and stirred for 45 minutes. After returning to room temperature, the reaction solution was concentrated under reduced pressure to obtain intermediate I2.

[0133] Organic compound E is organic compound p37-37 and is represented by the following formula (11).

Chemical formula

[0134] The high-precision calculation results of organic compounds C, D, and E are shown in Table 2.

Table 2

[0135] <Luminescence property evaluation> The luminescence spectra of a toluene solution of organic compound C (concentration: 8.0 × 10 -5 M) and a mixed thin film (concentration: 10 wt%) with 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) prepared by vacuum evaporation were measured using a Fluoromax-4 fluorescence spectrophotometer manufactured by HORIBA. The luminescence quantum yields of the toluene solution and the mixed thin film of organic compound C were measured using an integrating sphere C9920 manufactured by Hamamatsu Photonics. The luminescence lifetime τ of the toluene solution and the mixed thin film of organic compound C was measured using a Fluorolog-3 fluorescence lifetime measurement device manufactured by HORIBA. The luminescence lifetime τ can also be referred to as the delayed fluorescence lifetime. The above measurements were performed with an excitation light wavelength of 370 nm under an inert nitrogen atmosphere. Also, the measurement of the delayed fluorescence lifetime τ was performed by changing the temperature using a cryostat CoolSpeK manufactured by UNISOKU. The temperature dependence of the obtained delayed fluorescence lifetime τ was analyzed using Equation (3) assuming the thermal equilibrium between S1 and T1, and the experimental values of the energy difference ΔE ST and the radiative deactivation rate constant k r were estimated.

Equation

[0136] Similar to organic compound C, toluene solutions of organic compounds D, E, F, G, H, I, J, K, L, and M were prepared and their luminescence properties were evaluated.

[0137] Organic compound F is organic compound p1-151 and is represented by the following formula (12).

Chemical formula

[0138] Organic compound G is organic compound p7-151 and is represented by the following formula (13).

Chemical formula

[0139] Organic compound H is organic compound p7-107 and is represented by the following formula (14). [Chemical formula] The synthesis of organic compound H was carried out as follows. Cyanuric acid chloride (100 mg, 0.36 mmol) was dissolved in toluene (3 mL), and piperidine (36 mL, 0.36 mmol) was added at room temperature. After 5 minutes, the temperature was raised to 100 °C, stirred for 30 minutes, and then returned to room temperature. Aluminum chloride (106 mg, 0.79 mmol) was added, stirred at 100 °C for 1 hour, then returned to room temperature, and water was added. The organic layer was separated, dried over sodium sulfate, concentrated, and column purified (AcOEt: CHCl3 = 0:100 - 1:20) to obtain the target product. The obtained yellow solid organic compound H was 19 mg (0.044 mmol, 12.1%). 1 H NMR (600 MHz, CDCl3) δ [ppm] = 1.68 - 1.72 (m, 6H), 2.44 (s, 6H), 3.99 (br s, 4H), 7.29 (d, J = 7.8 Hz, 4H), 8.44 (d, J = 7.8 Hz, 4H)

[0140] Organic compound I is organic compound p64-166 and is represented by the following formula (15). [Chemical formula] The synthesis of organic compound I was carried out as follows. To a dichloromethane (11.8 mL) solution of intermediate I3 (608 μL, 4.3 mmol) represented by the following formula (16) at room temperature, aluminum chloride (616 mg, 4.6 mmol) was added and stirred for 40 minutes. A dichloromethane (12 mL) solution of Compound 2 was slowly added, and the mixture was stirred at room temperature for 20.5 hours. An aqueous 1 M sodium hydroxide solution (16 mL) was added at 0 °C, and the mixture was stirred at room temperature for 4 hours, then filtered through celite. After adding an aqueous 20% sodium chloride solution to the reaction solution, the organic layer was separated, dried over anhydrous sodium sulfate, concentrated, and purified by column chromatography (CH2Cl2 - CH2Cl2:MeOH = 9:1) to obtain a crude product (117 mg). The crude product was purified by preparative column chromatography (SunFire, Hexane / EtOAc = 82:18) to obtain organic compound I as the first peak. The obtained yellow solid organic compound I was 8.4 mg (0.015 mmol, 1.4%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 0.80 - 0.92 (br, 2H), 1.20 - 1.38 (br, 2H), 1.38 - 1.50 (br, 2H), 1.69 - 1.79 (br, 2H), 2.01 - 2.11 (br, 2H), 2.41 (s, 12H), 3.80 (s, 6H), 3.87 - 3.96 (br, 1H), 6.60 (s, 4H) [Chemical formula]

[0141] The synthesis of intermediate I3 was carried out as follows. Diisopropylethylamine (93 μL, 0.54 mmol) and cyclohexanethiol (66 μl, 0.54 mmol) were added to a toluene (8.9 mL) suspension of a cyanuric acid chloride·potassium chloride mixture (536 mg, 1.1 mmol) at room temperature, and then the mixture was heated to reflux for 14 hours. After cooling to room temperature and filtering the insoluble matter, intermediate I3 was obtained by concentration under reduced pressure.

[0142] Organic compound J is organic compound p107 - 4 and is represented by the following formula (17). [Chemical formula] The synthesis of organic compound J was carried out as follows. To a solution of aluminum chloride (133 mg, 1.0 mmol) and methoxybenzene (41 μL, 0.38 mmol) in dichloromethane (3 mL) was added cyanuric acid chloride (70 mg, 0.25 mmol) at 0 °C. After 10 minutes, the reaction solution was warmed to room temperature and stirred for 17 hours. An excess amount of piperidine (0.5 mL) was added and stirred for 30 minutes, and then diluted with water and chloroform. After concentrating the separated organic layer, purification was performed by column (CH2Cl2 100% - AcOEt:CH2Cl2 = 1: 4), and the target product was obtained. The obtained yellow solid organic compound J was 6.8 mg (0.015 mmol, 6.1 %). 1 H NMR (600 MHz, CDCl3) δ [ppm] = 1.64 - 1.69 (m, 12H), 3.91 (t, 4H), 3.95 (t, 4H), 6.93 (d, J = 9 Hz, 2H), 8.48 (d, J = 8.4 Hz, 2H) 13 C NMR (600 MHz, CDCl3) δ [ppm] = 24.44, 26.16, 45.50, 55.44, 113.47, 127.71, 132.10, 155.21, 156.09, 161.40, 163.88, 172.87 MS (FD-TOF): 445.2342 [M] + , calcd. for C 23 H 27 N9O (445.2339)

[0143] Organic compound K is organic compound p107-107 and is represented by the following formula (18).

Chemical formula

[0144] Organic compound L is organic compound p105-105 and is represented by the following formula (19).

Chemical formula

[0145] Organic compound M is organic compound p144-144 and is represented by the following formula (20).

Chemical formula

[0146] (Luminescence properties of organic compound C) Organic compound C showed blue luminescence with a maximum emission wavelength of 449 nm in toluene solution (see Fig. 57). The luminescence quantum yield of organic compound C in toluene solution was as high as 74%, and it showed a short luminescence lifetime τ of 214 ns. From the temperature dependence of the luminescence lifetime τ, the energy difference ΔE ST was estimated to be -6 meV, and the radiative decay rate constant k r was estimated to be 1.1 × 10 7 s -1 (see Figs. 58 and 59).

[0147] (Luminescence properties of organic compound D) Organic compound D showed blue luminescence with a maximum emission wavelength of 442 nm in toluene solution (see Fig. 60). The luminescence quantum yield of organic compound D in toluene solution was as high as 67%, and it showed a short luminescence lifetime τ of 565 ns. From the temperature dependence of the luminescence lifetime τ, the energy difference ΔE ST was estimated to be 47 meV, and the radiative decay rate constant k r was estimated to be 3.2 × 10 7 s -1 (see Figs. 61 and 62).

[0148] (Luminescence properties of organic compound E) Organic compound E showed green emission with a maximum emission wavelength of 518 nm in a toluene solution (see Fig. 63). The emission quantum yield of organic compound E in the toluene solution was 12%. No delayed fluorescence was observed from the transient emission decay measurement, and only fluorescence with an emission lifetime τ of 90 ns was shown (see Fig. 64).

[0149] (Luminescence properties of organic compounds F - M) The luminescence properties of organic compounds F, G, H, I, J, K, L, and M are shown in Table 3. In addition, the luminescence properties of the above - mentioned organic compounds C, D, and E are also described in Table 3 for reference.

[0150] As shown in Table 3, in a toluene solution, organic compounds F and G showed a negative energy difference ΔE ST similar to organic compound C. Organic compound H showed a positive energy difference ΔE ST similar to organic compound D. Organic compounds I, J, K, L, and M did not show delayed fluorescence, similar to organic compound E.

Table 3

[0151] <Organic light - emitting device evaluation> A glass substrate with indium tin oxide (ITO) with a thickness of 130 nm was ultrasonically cleaned in the order of neutral detergent, ultrapure water, acetone, and 2 - propanol, boiled in 2 - propanol, and then subjected to UV - ozone treatment for 30 minutes. On this ITO - coated glass substrate, poly(3,4 - ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (Clevious manufactured by Hereaeus) diluted to 60% with ultrapure water TMAfter spin-coating the dispersion of CH8000) in the air and drying it at 200 °C for 10 minutes, PEDOT:PSS with a film thickness of 30 nm was formed. Then, by vacuum evaporation, molybdenum trioxide (MoO3) with a film thickness of 5 nm, 4,4′′-bis(triphenylsilanyl)-(1,1′,4′,1′′)-terphenyl (BST) with a film thickness of 3 nm, bis(4-(dibenzo[b,d]furan-4-yl)phenyl)diphenylsilane (DBFSiDBF) layer with a film thickness of 10 nm, a mixed film of 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) and organic compound C (10 wt%) with a film thickness of 15 nm, PPF with a film thickness of 10 nm, tris(8-hydroxyquinolinato)aluminium (Alq3) with a film thickness of 40 nm, (8-hydroxyquinolinato)lithium (Liq) with a film thickness of 1 nm, and aluminium with a film thickness of 100 nm were formed to fabricate an organic light-emitting device. The light-emitting area of the organic light-emitting device is 2.0 × 2.0 mm 2 is. The structural formulas of PEDOT, PSS, BST, DBFSiDBF, PPF, Alq3, and Liq are as follows. [Chemical formula]

[0152] Similarly, an organic light-emitting device was fabricated using 2,4,5,6-tetra(carbazol-9-yl)isophthalonitrile (4CzIPN) instead of organic compound C.

[0153] The current density-voltage-luminance characteristics of the fabricated organic light-emitting device were measured using a Keithley 2400 source meter manufactured by Tektronix and a CS-200 luminance meter manufactured by Konica Minolta. The EL spectrum was measured using a PMA-11 multi-channel spectrometer manufactured by Hamamatsu Photonics. The transient luminescence decay was measured using a H7826 optical sensor manufactured by Hamamatsu Photonics, a 33220A function generator manufactured by Agilent, and a DPO3052 oscilloscope manufactured by Tektronix by applying a pulsed voltage (maximum 8 V, minimum -4 V) at a frequency of 1 kHz.

[0154] The organic light-emitting device using organic compound C showed blue luminescence from organic compound C at a current of 0.1 mA to 5.0 mA (see Fig. 65). Also, this organic light-emitting device showed good current density-voltage-luminance characteristics without leakage current or the like (see Fig. 66). In this organic light-emitting device, the maximum external quantum efficiency of organic compound C reached 17% (see Fig. 67). From these results, it was found that organic compound C can convert triplet excitons into singlet excitons and can be used as an organic light-emitting device. Furthermore, compared with 4CzIPN, which is a general TADF material, organic compound C in this organic light-emitting device showed fast transient luminescence decay (see Fig. 68). This is because of the negative energy difference ΔE of organic compound C ST which results in the rapid conversion of triplet excitons into singlet excitons and can be utilized as luminescence.

[0155] <Other organic compounds> In addition to the above-described organic compounds C to M, organic compounds p4-107, p4-4, p37-118, p139-139, p141-141, p142-142, p140-140, p162-162, and p65-166 were synthesized.

[0156] Organic compound p4-107 is represented by the following formula (21).

Chemical formula

[0157] Organic compound p4-4 is represented by the following formula (22).

Chemical formula

[0158] The organic compound p37-118 is represented by the following formula (23).

Chemical formula

[0159] The organic compound p139-139 is represented by the following formula (24).

Chemical formula

[0160] Organic compound p141-141 is represented by the following formula (25).

Chemical formula

[0161] The synthesis of intermediate I4 was carried out as follows. Cyanuric chloride (314 mg, 1.1 mmol) was dissolved in toluene (5 mL), and 3,5-dimethylpyrazole (362 mg, 3.8 mmol) and N,N-diisopropylethylamine (969 mL, 5.7 mmol) were added at room temperature under an argon atmosphere. After 40 minutes, the temperature was raised to 70 °C, and after another 20 minutes, to 90 °C, followed by stirring for 2 hours. After returning to room temperature and adding water, the mixture was extracted with chloroform, the organic layer was dried over sodium sulfate, and concentrated. Purification was performed by column chromatography (MeOH:CHCl3 = 1:99 - 10:90) to obtain the target product. The obtained intermediate I4 as a pale yellow solid was 490 mg (1.08 mmol, 94%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 2.34 (s, 9H), 2.76 (s, 9H), 6.11 (s, 3H) MS (MALDI-TOF): 456.54 [calcd:455.20]

[0162] Organic compound p142-142 is represented by the following formula (27). [Chem.] The synthesis of organic compound p142-142 was carried out as follows. Cyanuric chloride (358 mg, 1.3 mmol) was dissolved in tetrahydrofuran (3 mL), and 1-butanol (3 mL) and N,N-diisopropylethylamine (1.1 mL, 6.5 mmol) were added at room temperature under an argon atmosphere. After addition, the temperature was raised to 70 °C, and after another 2 hours, to 90 °C, followed by stirring for 1.5 hours. After returning to room temperature and adding water, the mixture was extracted with chloroform, the organic layer was dried over sodium sulfate, and concentrated. Purification was performed by column chromatography (AcOEt:CH2Cl2 = 1:99 - 10:90) to obtain the target product. The obtained organic compound p142-142 as a white solid was 374 mg (0.96 mmol, 74%). 1 1H NMR (600 MHz, CDCl3) δ [ppm] = 0.95 (t, 9H), 1.45 (tq, 6H), 1.76 (tt, 6H), 4. 47 (t, 6H), MS (MALDI-TOF): 390.64 [calcd: 389.22]

[0163] The organic compound p140-140 is represented by the following formula (28).

Chemical formula

[0164] The organic compound p162-162 is represented by the following formula (29).

Chemical formula

[0165] The organic compound p65-166 is represented by the following formula (30).

Chemical formula

[0166] The crude product was purified by preparative column (SunFire, Hexane / EtOAc = 82 : 18), and as the second peak, an organic compound represented by the following formula (31) was obtained. The obtained yellow solid organic compound was 22.4 mg (0.040 mmol, 3.8%). 1 1H NMR (600 MHz, CDCl3) δ [ppm] = 0.80 - 0.92 (br, 2H), 1.20 - 1.38 (br, 2H), 1.38 - 1.50 (m, 2H), 1.68 - 1.77 (br, 2H), 2.00 - 2.10 (br, 2H), 2.31 (s, 3H), 2.32 (s, 3H), 2.41 (s, 6H), 3.78 (s, 3H), 3.79 (s, 3H), 3.86 - 3.98 (br, 1H), 6.58 (s,1H), 6.59 (s, 2H), 6.64 (s, 1H)

Chemical formula

[0167] [Supplementary matters] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Industrial applicability]

[0168] The present invention can be used as a luminescent material.

Claims

1. An organic light-emitting device comprising a light-emitting layer containing a dopant compound and a host compound, The host compound is an organic compound having a lone pair of electrons and a π electron orbital, and the energy level E of the lowest singlet excited state S １ from the lowest triplet excited state T Ｓ１ of the energy level E １ is the energy difference ΔE obtained by subtracting the energy level E Ｔ１ from the lowest triplet excited state T ＳＴ is an organic compound having an experimental value in a toluene solution of -0.20 eV ≤ ΔE ＳＴ < 0 eV, an organic light-emitting device.

2. The organic light-emitting device according to claim 1, wherein the host compound is a heptazine derivative having a lone pair and a π electron orbital, is represented by the following formula (1), and has arbitrary substituents R1, R2, R3. 【Chemical 1】

3. The radiative deactivation rate constant k of the host compound ｒ is 1.0 × 10 ６ s －１ < k ｒ The organic light-emitting device according to claim 1, wherein the organic light-emitting device is such that

4. The organic light-emitting device according to claim 2, wherein the substituents R1, R2, R3 are composed of two types of substituents.

5. The organic light-emitting device according to claim 2, wherein the substituents R1, R2, R3 are each composed of three different types of substituents.

6. The organic light-emitting device according to claim 2, wherein the substituents R1, R2, R3 are composed of one type of substituent.

7. Among the substituents R1, R2, R3, taking the same substituent as the substituents R2, R3, the substituent R1 has a structure represented by the following formula (2), —S—R31, —O—R31, or —N—(R32)R33... (2) wherein R31 to R33 are each independently a linear or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent, and each of the substituents R2, R3 is a phenyl group or a phenyl group having one to three substituents. The organic light-emitting device according to claim 4.

8. The substituent R1 is any of the structures shown below, 【Chemical 2】 and each of the substituents R2, R3 is any of the structures shown below. The organic light-emitting device according to claim 2. [Chemical Formula 3] (However, excluding those shown below.) 【Chemical Formula 4】

9. The organic light-emitting device according to claim 6, wherein the substituents R1, R2, R3 are any of the structures shown below. 【Chemical Formula 5】

10. An organic light-emitting device comprising a light-emitting layer containing a dopant compound and a host compound, The dopant compound is an organic compound having a lone pair of electrons and a π electron orbital, and the energy level E １ of the lowest singlet excited state S Ｓ１ minus the energy level E １ of the lowest triplet excited state T Ｔ１ results in an energy difference ΔE ＳＴ such that, in a toluene solution, the experimental value satisfies -0.20 eV ≤ ΔE ＳＴ < 0 eV. The organic compound is an organic light-emitting device.

11. The organic light-emitting device according to claim 10, wherein the dopant compound is a heptazine derivative having a lone pair and a π electron orbital, is represented by the following formula (1), and has arbitrary substituents R1, R2, R3. 【Chemical Formula 6】

12. The radiative deactivation rate constant k of the dopant compound ｒ is 1.0 × 10 ６ s －１ < k ｒ The organic light-emitting device according to claim 10, wherein.

13. The organic light-emitting device according to claim 11, wherein the substituents R1, R2, R3 are composed of two types of substituents.

14. The organic light-emitting device according to claim 11, wherein the substituents R1, R2, R3 are each composed of three different types of substituents.

15. The organic light-emitting device according to claim 11, wherein the substituents R1, R2, R3 are composed of one type of substituent.

16. Among the substituents R1, R2, and R3, when the same substituent is used as substituents R2 and R3, substituent R1 has a structure represented by the following formula (2): -S-R31, -O-R31, or -N-(R32)R33... (2) Here, R31 to R33 are each independently a linear or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent. The organic light-emitting device according to claim 13, wherein each of the substituents R2 and R3 is a phenyl group or a phenyl group having 1 to 3 substituents.

17. Substituent R1 is any of the structures shown below, 【Chemical Formula 7】 The organic light-emitting device according to claim 11, wherein each of the substituents R2 and R3 is any of the structures shown below. 【Chemical 8】 (However, except for those shown below.) 【Chemical Formula 9】

18. The organic light-emitting device according to claim 15, wherein the substituents R1, R2, and R3 are any of the structures shown below. 【Chemical 10】

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