Light-emitting material consisting of pyrometenboron complex and light-emitting device using the same

Abstract

To provide a light-emitting element material capable of obtaining a light-emitting element with excellent element efficiency and durability.SOLUTION: The invention provide a light-emitting element material formed by an asymmetric pyrromethene boron complex, having a specific substituent group at a specific position of a pyrromethene skelton.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a light-emitting material comprising a pyrometenboron complex and a light-emitting device using the same. [Background technology]

[0002] Organic thin-film light-emitting devices, which emit light when electrons injected from the cathode and holes injected from the anode recombine within a light-emitting layer sandwiched between the two electrodes, have features such as the ability to be made thin, operate at a low driving voltage, have high brightness, and emit multi-color light. In particular, by combining a host material and a dopant material in the light-emitting layer, it is possible to obtain light-emitting devices that exhibit the three primary colors of blue, green, and red with high efficiency.

[0003] Various pyrometenboron complexes with different structures have been reported as dopant materials capable of providing high-brightness and high-purity light-emitting elements (see, for example, Patent Document 1). In recent years, light-emitting elements combining TADF (Thermally Activated Delayed Fluorescence) materials and pyrometenboron complexes have been investigated in order to achieve higher device efficiency (see, for example, Patent Documents 2-3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2009 / 116456 [Patent Document 2] International Publication No. 2016 / 056559 [Patent Document 3] International Publication No. 2019 / 013063 [Overview of the project] [Problems that the invention aims to solve]

[0005] According to the studies of the present inventors, in a light-emitting device using a dopant material, recombination of electrons and holes may occur on the dopant material (pyromethene boron complex), and as a result, it has been revealed that there is a problem that the device efficiency and durability of the light-emitting device are reduced. Therefore, an object of the present invention is to provide a light-emitting device material capable of obtaining a light-emitting device excellent in device efficiency and durability.

Means for Solving the Problems

[0006] The present invention is a light-emitting device material containing a pyromethene boron complex represented by the following general formula (1).

[0007]

Chemical formula

[0008] In the above general formula (1), R 1 ~R 4 may be the same or different, and each is independently selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted cycloalkyl group. R 5 and R 6One of them is selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted alkynyl group, a hydroxyl group, a thiol group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl ether group, a substituted or unsubstituted arylthioether group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siloxanyl group, and a substituted or unsubstituted boryl group, and the other is a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted alkynyl group, a hydroxyl group, a thiol group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl ether group, a substituted or unsubstituted arylthioether group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siloxanyl group, and a substituted or unsubstituted boryl group. However, R 5 and R 6 are different groups.

[0009] X 1 and X 2 may be the same or different and are selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a hydroxyl group, a halogen atom, and a cyano group.

[0010] R 7 is selected from the group consisting of a substituted or unsubstituted aryl group and a substituted or unsubstituted heteroaryl group.

Advantages of the Invention

[0011] The light-emitting element material of the present invention makes it possible to obtain light-emitting elements with excellent element efficiency and durability. [Modes for carrying out the invention]

[0012] The following describes in detail preferred embodiments of the light-emitting material and light-emitting device comprising the pyrometenboron complex according to the present invention. However, the present invention is not limited to the following embodiments and can be implemented with various modifications depending on the purpose and application.

[0013] <Pyrometenboron complex> The pyrometenboron complex used in the present invention is represented by the following general formula (1).

[0014] [ka]

[0015] In the above general formula (1), R 1 ~R 4 These substituents may be the same or different, and each is independently selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. By selecting these substituents, energy deactivation due to intramolecular rotation can be suppressed, thereby improving device efficiency and durability.

[0016] R 5 and R 6One of the groups is selected from the group consisting of substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted cycloalkenyl groups, substituted or unsubstituted alkynyl groups, hydroxyl groups, thiol groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted alkylthio groups, substituted or unsubstituted aryl ether groups, substituted or unsubstituted arylthioether groups, substituted or unsubstituted heterocyclic groups, substituted or unsubstituted amino groups, substituted or unsubstituted silyl groups, substituted or unsubstituted siloxanyl groups, and substituted or unsubstituted boryl groups, and the other is a hydrogen atom, substituted or unsubstituted A The substituents are selected from the group consisting of a lucyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted alkynyl group, a hydroxyl group, a thiol group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl ether group, a substituted or unsubstituted arylthioether group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siloxanyl group, and a substituted or unsubstituted boryl group. By selecting these substituents, the interaction between pyrometenboron complexes can be suppressed by steric hindrance, thereby improving the efficiency of the device.

[0017] However, R 5 and R 6 These are different groups. In this explanation, "different groups" refers to groups that have different structures from each other. For example, although methyl and ethyl groups are both alkyl groups, they have different structures and therefore qualify as "different groups" in this explanation.

[0018] As mentioned above, electron-hole recombination may occur on the dopant material (pyromeneboron complex), and one possible reason for this is that electrons are trapped in the light-emitting material. For example, in a light-emitting material combining a pyrometenboron complex and a TADF material, it is desirable for electron-hole recombination to occur in the TADF material. However, if the LUMO level of the dopant material is deep, electron transfer from the TADF material to the dopant material is likely to occur, and electron trapping reduces the device efficiency and durability of the light-emitting element. Therefore, in the present invention, we investigated how to suppress electron transfer by making the LUMO level of the pyrometenboron complex in the light-emitting material shallower, and as a result, R 5 and R 6 We discovered that by using an asymmetric pyrometenboron complex with different groups, electron trapping by the pyrometenboron complex in the light-emitting material can be suppressed, thereby improving the device efficiency and durability of the light-emitting device.

[0019] In this invention, R 5 and R 6 It is preferable that one of the substituents is selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. By selecting these substituents, intramolecular rotation can be suppressed, improving the fluorescence quantum yield and further enhancing the device efficiency. Furthermore, by selecting these substituents, vibrational relaxation in the excited state of the pyrometenboron complex can be suppressed, reducing the full width at half maximum of the emission spectrum and improving color purity. In this case, it is even more preferable that the other substituent is hydrogen.

[0020] X 1 and X 2These may be the same or different, and are selected from the group consisting of substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted aryl ether groups, hydroxyl groups, halogen atoms, and cyano groups. Among these, alkyl groups substituted with at least one halogen, alkoxy groups substituted with at least one halogen, aryl ether groups substituted with at least one halogen, aryl groups substituted with at least one halogen, halogen atoms, and cyano groups are preferred because their electron-withdrawing properties can lower the electron density of the pyromethene skeleton, stabilize the excited state, and further improve device efficiency and durability. Furthermore, from the viewpoint of further stabilizing the excited state to obtain a higher fluorescence quantum yield and further improving durability, X 1 and X 2 It is more preferable that it be a fluorine atom.

[0021] R 7 R is selected from the group consisting of substituted or unsubstituted aryl groups and substituted or unsubstituted heteroaryl groups. As mentioned above, the pyrometenboron complex represented by general formula (1) preferably has a shallow LUMO level. From this viewpoint, 7 If the compound contains an electron-deficient heteroaryl group, it is preferable that such a heteroaryl group does not directly bond to the pyromethene skeleton. Here, an electron-deficient heteroaryl group means a monovalent group derived from an electron-deficient aromatic heterocycle. Also from a similar viewpoint, 7 If the material contains a phenyl group having an electron-withdrawing group, it is preferable that such a phenyl group does not directly bond to the pyromethene skeleton.

[0022] Examples of electron-deficient heteroaryl groups include monovalent groups derived from pyridine rings, pyrazine rings, pyridazine rings, pyrimidine rings, triazine rings, quinoline rings, isoquinoline rings, quinoxaline rings, quinazoline rings, naphthyridine rings, acridine rings, phenazine rings, benzoquinoline rings, benzoisoquinoline rings, phenanthridine rings, phenanthroline rings, benzoquinone rings, coumarin rings, anthraquinone rings, fluorenone rings, and the like.

[0023] Examples of electron-withdrawing groups include carbonyl groups, sulfonyl groups, cyano groups, and halogens.

[0024] In this explanation, "unsubstituted" means that the only atoms bonded to the target basic skeleton or functional group are hydrogen atoms or deuterium atoms.

[0025] Furthermore, in all groups, hydrogen may be replaced with deuterium. The same applies to the compounds or substructures described below.

[0026] Alkyl groups refer to saturated aliphatic hydrocarbon groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl groups, and may or may not have substituents. There are no particular restrictions on additional substituents when substitution occurs; for example, alkyl groups, halogens, aryl groups, heteroaryl groups, etc., can be used, and this point is also common to the following description. Furthermore, the number of carbon atoms in the alkyl group is not particularly limited, but from the standpoint of availability and cost, it is preferably in the range of 1 to 20, more preferably 1 to 8.

[0027] A cycloalkyl group refers to a saturated alicyclic hydrocarbon group such as a cyclopropyl group, cyclohexyl group, norbornyl group, or adamantyl group, and may or may not have substituents. The number of carbon atoms in the alkyl group is not particularly limited, but is preferably in the range of 3 to 20.

[0028] An alkenyl group refers to an unsaturated aliphatic hydrocarbon group containing a double bond, such as a vinyl group, an allyl group, or a butadienyl group, which may or may not have substituents. The number of carbon atoms in the alkenyl group is not particularly limited, but is preferably in the range of 2 to 20.

[0029] A cycloalkenyl group refers to an unsaturated alicyclic hydrocarbon group containing a double bond, such as a cyclopentenyl group, cyclopentadienyl group, or cyclohexenyl group, and may or may not have substituents.

[0030] An alkynyl group refers to an unsaturated aliphatic hydrocarbon group containing a triple bond, such as an ethynyl group, and may or may not have substituents. The number of carbon atoms in the alkynyl group is not particularly limited, but is preferably in the range of 2 to 20.

[0031] An alkoxy group refers to a functional group in which an aliphatic hydrocarbon group is bonded via an ether linkage, such as a methoxy group, ethoxy group, or propoxy group, and this aliphatic hydrocarbon group may or may not have substituents. The number of carbon atoms in the alkoxy group is not particularly limited, but is preferably in the range of 1 to 20.

[0032] An alkylthio group is a group in which the oxygen atom of the ether bond of an alkoxy group is replaced by a sulfur atom. The hydrocarbon group of the alkylthio group may or may not have substituents. The number of carbon atoms in the alkylthio group is not particularly limited, but is preferably in the range of 1 to 20.

[0033] An aryl ether group refers to a functional group in which an aromatic hydrocarbon group is bonded via an ether bond, such as a phenoxy group, and the aromatic hydrocarbon group may or may not have substituents. The number of carbon atoms in the aryl ether group is not particularly limited, but is preferably in the range of 6 to 40.

[0034] An arylthioether group is an aryl ether group in which the oxygen atom in the ether bond is replaced by a sulfur atom. The aromatic hydrocarbon group in the arylthioether group may or may not have substituents. The number of carbon atoms in the arylthioether group is not particularly limited, but is preferably in the range of 6 to 40.

[0035] A heterocyclic group refers to an aliphatic ring containing atoms other than carbon, such as a pyran ring, a piperidine ring, or a cyclic amide, which may or may not have substituents. The number of carbon atoms in the heterocyclic group is not particularly limited, but is preferably in the range of 2 to 20.

[0036] An amino group is a substituted or unsubstituted amino group. Examples of substituents include aryl groups, heteroaryl groups, linear alkyl groups, and branched alkyl groups. Preferred aryl and heteroaryl groups are phenyl, naphthyl, pyridyl, and quinolinyl groups. These substituents may be further substituted. The number of carbon atoms is not particularly limited, but is preferably in the range of 2 to 50, more preferably 6 to 40, and most preferably 6 to 30.

[0037] A silyl group refers to a functional group to which a substituted or unsubstituted silicon atom is bonded. Examples include alkylsilyl groups such as trimethylsilyl, triethylsilyl, tert-butyldimethylsilyl, propyldimethylsilyl, and vinyldimethylsilyl, and arylsilyl groups such as phenyldimethylsilyl, tert-butyldiphenylsilyl, triphenylsilyl, and trinaphthylsilyl. The substituent on the silicon may be further substituted. The number of carbon atoms in the silyl group is not particularly limited, but is preferably in the range of 1 to 30.

[0038] A siloxanyl group refers to a silicon compound group via an ether bond, such as a trimethylsiloxanyl group. Substituents on the silicon may be further substituted.

[0039] A boryl group is a substituted or unsubstituted boryl group. Examples of substituents include aryl groups, heteroaryl groups, linear alkyl groups, branched alkyl groups, aryl ether groups, alkoxy groups, and hydroxyl groups, with aryl groups and aryl ether groups being preferred.

[0040] The aryl group refers to aromatic hydrocarbon groups such as phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, benzofluorenyl, dibenzofluorenyl, phenanthryl, anthracenyl, benzophenanthryl, benzoanthracenyl, chrysenyl, pyrenyl, fluoranthenyl, triphenylenyl, benzofluoranthenyl, dibenzoanthracenyl, perilenyl, and hericenyl groups. Among these, phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, phenanthryl, anthracenyl, pyrenyl, fluoranthenyl, and triphenylenyl groups are preferred. The aryl group may or may not have substituents. The number of carbon atoms in the aryl group is not particularly limited, but is preferably in the range of 6 to 40, more preferably 6 to 30. Furthermore, in the case of a phenyl group, if there are substituents on two adjacent carbon atoms within the phenyl group, these substituents may form a ring structure.

[0041] Heteroaryl groups refer to cyclic aromatic groups that have one or more non-carbon atoms in the ring, such as pyridyl, furanyl, thiophenyl, quinolinyl, isoquinolinyl, pyrazinyl, pyrimidyl, pyridadinyl, triazinyl, naphthilidinyl, synnolinyl, phthalazinyl, quinoxalinyl, quinazolinyl, benzofuranyl, benzothiophenyl, indolyl, dibenzofuranyl, dibenzothiophenyl, carbazolyl, benzocarbazolyl, carbolinyl, indrocarbazolyl, benzoflocarbazolyl, benzothienocarbazolyl, dihydroindenocarbazolyl, benzoquinolinyl, acridinyl, dibenzoacridinyl, benzimidazolyl, imidazopyridyl, benzoxazolyl, benzothiazolyl, and phenanthrolinyl groups. However, the naphthilidinyl group refers to any of the following: 1,5-naphthilidinyl group, 1,6-naphthilidinyl group, 1,7-naphthilidinyl group, 1,8-naphthilidinyl group, 2,6-naphthilidinyl group, or 2,7-naphthilidinyl group. The heteroaryl group may or may not have substituents. The number of carbon atoms in the heteroaryl group is not particularly limited, but is preferably in the range of 2 to 40, more preferably 2 to 30.

[0042] A halogen refers to an atom selected from fluorine, chlorine, bromine, and iodine.

[0043] A cyano group is a functional group whose structure is represented by -C≡N. In this case, it is bonded to a carbon atom.

[0044] In this invention, the structure represented by the following structural formula (2) is referred to as the pyromethene skeleton.

[0045] [ka]

[0046] An example of a pyrometenboron complex represented by general formula (1) is shown below, but is not limited to these.

[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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[0055]

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[0056]

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[0057]

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[0058] [ka]

[0059] [ka]

[0060] [ka]

[0061] The molecular weight of the pyrometenboron complex represented by general formula (1) is preferably 380 or higher from the viewpoint of thermal stability, as this suppresses thermal decomposition and allows for more stable improvement of device efficiency. A molecular weight of 400 or higher is more preferable.

[0062] The pyrometenboron complex represented by general formula (1) can be manufactured by referring to methods described in, for example, J.Org.Chem.,vol.64,No.21,pp.7813-7819 (1999), Angew.Chem.,Int.Ed.Engl.,vol.36,pp.1333-1335 (1997), and Org.Lett.,vol.12,pp.296 (2010). Methods for synthesizing pyrometenboron complexes from pyrroles with different structures include, for example, Tetrahedron Lett.,vol.56,pp.3919-3922 (2015) and Japanese Patent Publication No. 2010-83875.

[0063] The obtained pyrometenboron complex is preferably purified by organic synthesis methods such as recrystallization or column chromatography, and then further purified by reduced-pressure heating, commonly known as sublimation purification, to remove low-boiling point components and improve purity. The heating temperature in sublimation purification is not particularly limited, but from the viewpoint of preventing thermal decomposition of the pyrometenboron complex, it is preferably 330°C or lower, and more preferably 300°C or lower. From the viewpoint of stabilizing the light-emitting properties of the pyrometenboron complex, the purity of the pyrometenboron complex is preferably 99% by weight or higher.

[0064] The pyrometenboron complex represented by general formula (1) preferably exhibits emission observed in the region of peak wavelength between 500 nm and 550 nm when excited with excitation light. Hereafter, emission observed in the region of peak wavelength between 500 nm and 550 nm will be referred to as "green emission". From the viewpoint of expanding the color gamut and improving color reproducibility, it is more preferable to have a peak wavelength in the range of wavelength between 510 nm and 540 nm. Here, the emission spectrum of the pyrometenboron complex represented by general formula (1) is obtained by using toluene as the solvent at a concentration of 10⁻¹⁰. -5 The measurement can be performed using a fluorescence spectrophotometer with a mol / L diluted solution.

[0065] The pyrometenboron complex represented by general formula (1) preferably has a sharp emission spectrum from the viewpoint of further improving color purity. In particular, when used in top-emission type light-emitting devices, which are mainstream in display devices and lighting devices, the improvement in brightness and color purity due to the resonance effect of the microcavity structure is more pronounced the sharper the emission spectrum, and the device efficiency can be further improved. From this viewpoint, the full width at half maximum of the emission spectrum is preferably 45 nm or less, more preferably 35 nm or less, and even more preferably 30 nm or less.

[0066] The device efficiency of a light-emitting element depends on the fluorescence quantum yield of the light-emitting element material. Therefore, a fluorescence quantum yield close to 100% is desired for the light-emitting element material. The fluorescence quantum yield of the pyrometenboron complex represented by general formula (1) is preferably 80% or higher, and more preferably 85% or higher. Here, the fluorescence quantum yield of the pyrometenboron complex represented by general formula (1) is calculated using toluene as the solvent at a concentration of 10⁻¹⁰. -5 The absolute quantum yield can be measured using a mol / L diluted solution and an absolute quantum yield analyzer.

[0067] <Light-emitting material> The light-emitting element material according to the present invention refers to a material consisting of a pyrometenboron complex represented by general formula (1) and used in any layer of a light-emitting element. In other words, the light-emitting element material refers to the application of the pyrometenboron complex represented by the aforementioned general formula (1). Examples of light-emitting element materials include materials used in hole injection layers, hole transport layers, electron blocking layers, light-emitting layers, electron transport layers, electron injection layers, hole blocking layers and / or protective films (cap layers) of electrodes, which will be described later. Among these, it is preferably used in light-emitting layers because it has high device efficiency, color purity and thin-film stability.

[0068] <hibi> Next, embodiments of the light-emitting element of the present invention will be described. The light-emitting element of the present invention has a light-emitting layer containing the aforementioned light-emitting material between the anode and the cathode, and emits light in response to electrical energy.

[0069] The light-emitting element of the present invention may be either a bottom-emission type or a top-emission type. The light-emitting element of the present invention is more preferably of the top-emission type because it has a narrow full width at half maximum of the emission spectrum and excellent color purity. In a top-emission type light-emitting element, the element efficiency increases as the full width at half maximum decreases due to the resonance effect caused by the microcavity. Therefore, it is possible to achieve a higher level of both color purity and element efficiency.

[0070] In addition to configurations consisting only of an emissive layer, the layer configurations between the anode and cathode in such light-emitting devices include stacked configurations such as: 1) emissive layer / electron transport layer, 2) hole transport layer / emissive layer, 3) hole transport layer / emissive layer / electron transport layer, 4) hole injection layer / hole transport layer / emissive layer / electron transport layer, 5) hole transport layer / emissive layer / electron transport layer / electron injection layer, 6) hole injection layer / hole transport layer / emissive layer / electron transport layer / electron injection layer, 7) hole injection layer / hole transport layer / emissive layer / hole blocking layer / electron transport layer / electron injection layer, and 8) hole injection layer / hole transport layer / electron blocking layer / emissive layer / hole blocking layer / electron transport layer / electron injection layer.

[0071] Furthermore, the above-described laminated structure may be a tandem type in which multiple layers are stacked with an intermediate layer in between. Examples of intermediate layers include intermediate electrodes, intermediate conductive layers, charge generation layers, electron extraction layers, connecting layers, and intermediate insulating layers, and known material configurations can be used. Preferred specific examples of the tandem type include 9) hole transport layer / light-emitting layer / electron transport layer / charge generation layer / hole transport layer / light-emitting layer / electron transport layer, and 10) hole injection layer / hole transport layer / light-emitting layer / electron transport layer / electron injection layer / charge generation layer / hole injection layer / hole transport layer / light-emitting layer / electron transport layer / electron injection layer, which have two or more light-emitting layers between the anode and cathode, and include one or more charge-generating layers as intermediate layers between each light-emitting layer. Pyridine derivatives and phenanthroline derivatives are preferred materials for the intermediate layer.

[0072] Furthermore, each of the above layers may be a single layer or multiple layers, and may be doped. Another example of a device configuration is one that includes an anode, one or more organic layers including an emissive layer, a cathode, and further includes a layer using a capping material to improve device efficiency due to optical interference effects.

[0073] The following are specific examples of the configuration of a light-emitting element, but the configuration of the present invention is not limited to these.

[0074] (substrate) It is preferable to form the light-emitting element on a substrate in order to maintain the mechanical strength of the light-emitting element, minimize thermal deformation, and provide a barrier that prevents water vapor and oxygen from entering the light-emitting layer. The substrate is not particularly limited, but examples include glass plates, ceramic plates, resin films, resin thin films, and thin metal plates. Among these, glass substrates are preferably used from the viewpoint of transparency and ease of processing. In particular, for bottom-emission type light-emitting elements that extract light through the substrate, glass substrates with high transparency are preferred. Furthermore, flexible displays and foldable displays are increasing, mainly in mobile devices such as smartphones, and resin films or resin thin films cured with varnish are preferably used for these applications. Heat-resistant films are used as resin films, and specific examples include polyimide films and polyethylene naphthalate films.

[0075] Furthermore, the surface of the substrate may be provided with various wirings, circuits, and TFT switching elements for driving the organic EL.

[0076] (anode) The anode is preferably formed on the substrate. Various wirings, circuits, and switching elements may be interposed between the substrate and the anode. The material used for the anode is not particularly limited as long as it can efficiently inject holes into the organic layer, but in the case of a bottom-emission type light-emitting element, it is preferably a transparent or translucent electrode, and in the case of a top-emission type light-emitting element, it is preferably a reflective electrode.

[0077] Examples of materials for transparent or translucent electrodes include conductive metal oxides such as zinc oxide, tin oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); metals such as gold, silver, aluminum, and chromium; and conductive polymers such as polythiophene, polypyrrole, and polyaniline. However, when using metals, it is preferable to make the film thickness thin so that light can be semi-transparent. Among these, indium tin oxide (ITO) is more preferred from the viewpoint of transparency and stability.

[0078] The material of the reflective electrode is preferably one that does not absorb any light and has a high reflectivity, such as metals like aluminum, silver, and platinum.

[0079] Two or more of these electrode materials may be used, or multiple materials may be layered.

[0080] The film thickness of the anode is not particularly limited, but is preferably several nanometers to several hundred nanometers.

[0081] The method for forming the anode can be selected according to the material being formed, but examples include sputtering, vapor deposition, and inkjet. For example, sputtering is preferred when forming the anode with a metal oxide, and vapor deposition is preferred when forming the anode with a metal. The thickness of the anode is not particularly limited, but it is preferably several nanometers to several hundred nanometers.

[0082] (cathode) The cathode is formed on the surface opposite the anode, separated by an organic layer, and is particularly preferably formed on the surface of the electron transport layer or electron injection layer. The material used for the cathode is not particularly limited as long as it can efficiently inject electrons into the light-emitting layer, but in the case of a bottom-emission type light-emitting element, it is preferably a reflective electrode, and in the case of a top-emission type light-emitting element, it is preferably a translucent electrode.

[0083] Generally, metals such as platinum, gold, silver, copper, iron, tin, aluminum, and indium, alloys of these metals with low work function metals such as lithium, sodium, potassium, calcium, and magnesium, multilayer films, and conductive metal oxides such as zinc oxide, indium tin oxide (ITO), and indium zinc oxide (IZO) are preferred. Among these, aluminum, silver, and magnesium are preferred as main components from the viewpoint of electrical resistance, ease of film formation, film stability, and device efficiency. Furthermore, a composition of magnesium and silver is preferred because it facilitates electron injection into the electron transport layer and electron injection layer, and allows for a reduction in the driving voltage.

[0084] (protective layer) To protect the cathode, it is preferable to laminate a protective layer (cap layer) on the cathode. The material constituting the protective layer is not particularly limited, but examples include metals such as platinum, gold, silver, copper, iron, tin, aluminum, and indium; alloys using these metals; inorganic materials such as silica, titania, and silicon nitride; and organic polymer compounds such as polyvinyl alcohol, polyvinyl chloride, and hydrocarbon polymer compounds. However, in the case of a top-emission type light-emitting element, it is preferable to select the material used for the protective layer from materials that are light-transmitting in the visible light region.

[0085] (Hole injection layer) The hole injection layer is a layer inserted between the anode and the hole transport layer to facilitate hole injection. The hole injection layer may be a single layer or multiple layers stacked together. The presence of a hole injection layer between the hole transport layer and the anode allows for operation at lower voltages and improves durability. Furthermore, it improves the carrier balance of the device, leading to increased device efficiency.

[0086] A preferred example of a hole injection material is an electron-donating hole injection material (donor material). These materials have a HOMO level that is shallower than the hole transport layer and close to the anode's work function, thus reducing the energy barrier with the anode. Specifically, examples include aromatic amine materials such as benzidine derivatives, 4,4',4”-tris(3-methylphenyl(phenyl)amino)triphenylamine (m-MTDATA), 4,4',4”-tris(1-naphthyl(phenyl)amino)triphenylamine (1-TNATA), heterocyclic compounds such as carbazole derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxadiazole derivatives, phthalocyanine derivatives, and porphyrin derivatives, and polymers such as polycarbonates and styrene derivatives having the monomers in their side chains, polythiophenes such as PEDOT / PSS, polyaniline, polyfluorene, polyvinylcarbazole, and polysilane. Two or more of these materials may be used. Alternatively, multiple materials may be layered to form a hole injection layer.

[0087] Another preferred example of a hole injection material is an electron-accepting hole injection material (acceptor material). Here, the hole injection layer may be composed of the acceptor material alone, or it may be used by doping the donor material with the acceptor material. The acceptor material is a material that forms a charge transfer complex with the adjacent hole transport layer when used alone, and with the donor material when used by doping the donor material. Using such a material is preferable because it contributes to improving the conductivity of the hole injection layer and reducing the driving voltage of the device, thereby further improving the device efficiency and durability. Examples of acceptor materials include metal oxides such as molybdenum oxide, vanadium oxide, tungsten oxide, and ruthenium oxide; charge transfer complexes such as tris(4-bromophenyl)aminium hexachloroantimonate (TBPAH); n-type organic semiconductor compounds such as 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonnitrile (HAT-CN6), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), tetracyanoquinodimethane derivatives, radialene derivatives, fluorinated copper phthalocyanine, and fullerenes. When the hole injection layer contains an acceptor compound, the hole injection layer may be a single layer or may be composed of multiple layers stacked on top of each other.

[0088] (Hole transport layer and electron blocking layer) The hole transport layer is a layer that transports holes injected from the anode to the light-emitting layer, and the electron blocking layer is a layer that efficiently blocks the movement of electrons. Both the hole transport layer and the electron blocking layer may be single layers or multiple layers stacked together. They are formed by stacking or mixing hole transport materials. Furthermore, it is preferable that the hole transport material has high hole injection efficiency and efficiently transports the injected holes. To achieve this, it is required to be a material that has an appropriate ionization potential, high hole mobility, excellent stability, and does not easily generate impurities that act as traps.

[0089] Substances that satisfy these conditions are not particularly limited, but examples include benzidine derivatives, a group of aromatic amine materials called starburst arylamines, carbazole derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives, dibenzofuran derivatives, thiophene derivatives, benzothiophene derivatives, dibenzothiophene derivatives, fluorene derivatives, spirofluorene derivatives, oxadiazole derivatives, phthalocyanine derivatives, heterocyclic compounds such as porphyrin derivatives, and polymers such as polycarbonates and styrene derivatives having the monomers in their side chains, polythiophenes, polyanilines, polyfluorenes, polyvinylcarbazoles, and polysilanes.

[0090] (Emitting layer) The light-emitting layer is a layer that emits light due to the excitation energy generated by the recombination of holes and electrons. The light-emitting layer may be composed of a single material, but from the viewpoint of color purity, it is preferable to have a first compound and a second compound which is a dopant that exhibits strong luminescence. Suitable examples of the first compound include, for example, a host material that is responsible for charge transfer and a TADF material.

[0091] The pyrometenboron complex represented by general formula (1) is preferable to use as the second compound, which is a dopant in the luminescence layer, because it has particularly excellent fluorescence quantum yield, the peak wavelength of its emission spectrum is suitable for green emission, it has a narrow full width at half maximum, and it has excellent color purity. From the viewpoint of further suppressing the concentration quenching phenomenon, the content of the second compound in the luminescence layer is preferably 5% by weight or less, and more preferably 2% by weight or less. On the other hand, from the viewpoint of more efficient energy transfer, the content of the second compound in the luminescence layer is preferably 0.1% by weight or more, and more preferably 0.5% by weight or more.

[0092] The host material is not particularly limited, but examples include compounds having condensed aryl rings such as naphthacene, pyrene, anthracene, and fluorantene, and their derivatives; aromatic amine derivatives such as N,N'-dinaphthyl-N,N'-diphenyl-4,4'-diphenyl-1,1'-diamine; metal chelated oxynoide compounds including tris(8-quinolinate)aluminum(III); bisstyryl derivatives such as distyrylbenzene derivatives; tetraphenylbutadiene derivatives; indene derivatives; coumarin derivatives; oxadiazole derivatives; pyrrolopyridine derivatives; perinone derivatives; pyrrolopyrrole derivatives; thiadiazolopyridine derivatives; dibenzofuran derivatives; carbazole derivatives; indolocarbazole derivatives; triazine derivatives; and polymer derivatives such as polyphenylenevinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, and polythiophene derivatives. Two or more of these may be used, or two or more host materials may be laminated. Among these, carbazole derivatives, anthracene derivatives, and naphthacene derivatives are preferred.

[0093] The dopant material may contain fluorescent materials other than pyrometenoboron complexes represented by general formula (1). Specifically, examples include compounds having condensed aryl rings such as naphthacene, pyrene, anthracene, and fluorantene, and their derivatives; compounds having heteroaryl rings and their derivatives; distylylbenzene derivatives; aminostyryl derivatives; tetraphenylbutadiene derivatives; stilbene derivatives; aldazine derivatives; pyrometene derivatives; diketopyrrolo[3,4-c]pyrrole derivatives; coumarin derivatives; azole derivatives and their metal complexes; and aromatic amine derivatives. Two or more of these may be used.

[0094] Furthermore, a phosphorescent material may be included as the dopant material. Preferably, the phosphorescent material is a metal complex compound containing at least one metal selected from the group consisting of iridium (Ir), ruthenium (Ru), palladium (Pd), platinum (Pt), osmium (Os), and rhenium (Re), and from the viewpoint of high-efficiency emission, an iridium complex or a platinum complex is more preferred. The ligand preferably has a nitrogen-containing heteroaryl group such as a phenylpyridine skeleton, a phenylquinoline skeleton, or a carbene skeleton, but is not limited to these.

[0095] However, from the viewpoint of further improving color purity, it is preferable that the dopant material be only the pyrometenboron complex represented by general formula (1).

[0096] In addition to the host material or dopant material, the light-emitting layer may further contain a third component to adjust the carrier balance within the light-emitting layer or to stabilize the layer structure of the light-emitting layer. However, it is preferable to select a third component that does not interact with the host material and the dopant material.

[0097] TADF materials are materials that improve the probability of singlet exciton generation by reducing the energy gap between the singlet and triplet excited states, thereby promoting reverse intersystem crossing from the triplet excited state to the singlet excited state. By utilizing the delayed fluorescence due to this TADF mechanism, the theoretical internal efficiency can be increased to 100%. Furthermore, when a Förster-type energy transfer occurs from the singlet excited state of the first compound with thermally activated delayed fluorescence to the singlet excited state of the second compound, fluorescence emission from the singlet excited state of the second compound is observed. Here, if the second compound is a fluorescent material with a sharp emission spectrum, a light-emitting element with superior device efficiency and color purity can be obtained. Thus, when the light-emitting layer contains a thermally activated delayed fluorescence material, the device efficiency is further improved, contributing to lower power consumption of displays. The thermally activated delayed fluorescence material may be a single material that exhibits thermally activated delayed fluorescence, or it may be a material that exhibits thermally activated delayed fluorescence with multiple materials, such as when an excyplex complex is formed.

[0098] The thermally activated delayed fluorescence compound can be a single material or a combination of materials, and known materials can be used. Specifically, examples include benzonitrile derivatives, triazine derivatives, disulfoxide derivatives, carbazole derivatives, indolocarbazole derivatives, dihydrophenazine derivatives, thiazole derivatives, and oxadiazole derivatives. There are no particular limitations on such thermally activated delayed fluorescence compounds, but the following are some examples.

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[0107] Preferably, the first compound is a thermally activated delayed fluorescence compound, and the second compound is a compound having a pyromethene skeleton represented by the general formula (1). Furthermore, if the first compound is a thermally activated delayed fluorescence compound, it is preferable that the light-emitting layer further contains a third compound, and that the excitation singlet energy of the third compound is greater than the excitation singlet energy of the first compound. This allows the third compound to have the function of confining the energy of the light-emitting material within the light-emitting layer, making it possible to emit light efficiently.

[0108] The third compound is preferably an organic compound with high charge transport ability and a high glass transition temperature. While not particularly limited, the third compound can be considered as follows:

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[0120] (Electron transport layer and hole blocking layer) The electron transport layer is a layer into which electrons are injected from the cathode and then transported, while the hole blocking layer is a layer that efficiently blocks the movement of holes. The electron transport material used in the electron transport layer and hole blocking layer is required to have high electron affinity, high electron mobility, excellent stability, and be a substance that does not easily generate impurities that act as traps. Furthermore, from the viewpoint of suppressing film quality degradation due to crystallization, compounds with a molecular weight of 400 or more are preferred.

[0121] Examples of electron transport materials include polycyclic aromatic derivatives, styryl aromatic ring derivatives, quinone derivatives, phosphorus oxide derivatives, quinolinol complexes such as tris(8-quinolinolate)aluminum(III), benzoquinolinol complexes, hydroxyazole complexes, azomethine complexes, tropolone metal complexes, and flavonol metal complexes. From the viewpoint of reducing the driving voltage and further improving the device efficiency, it is preferable to use compounds having a heteroaryl group containing electron-accepting nitrogen. Here, electron-accepting nitrogen refers to a nitrogen atom that forms a multiple bond with an adjacent atom. Heteroaryl groups containing electron-accepting nitrogen have a high electron affinity, making it easier for electrons to be injected from the cathode, thus enabling lower voltage driving. In addition, the supply of electrons to the light-emitting layer increases, and the recombination probability increases, further improving the device efficiency. Examples of compounds having a heteroaryl group structure containing electron-accepting nitrogen include pyridine derivatives, triazine derivatives, pyrazine derivatives, pyrimidine derivatives, quinoline derivatives, quinoxaline derivatives, quinazoline derivatives, naphthyridine derivatives, benzoquinoline derivatives, phenanthroline derivatives, imidazole derivatives, oxazole derivatives, thiazole derivatives, triazole derivatives, oxadiazole derivatives, thiadiazole derivatives, benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, phenanthroimidazole derivatives, and oligopyridine derivatives such as bipyridine and terpyridine. Two or more of these may be used.

[0122] Furthermore, it is more preferable if the electron transport material has a condensed polycyclic aromatic skeleton, as this improves the glass transition temperature, increases electron mobility, and allows for a reduction in driving voltage. Preferred condensed polycyclic aromatic skeletons include quinolinol complexes, triazine derivatives, fluorantene skeletons, anthracene skeletons, pyrene skeletons, or phenanthroline skeletons.

[0123] The electron transport layer may contain a donor material. Here, a donor material is a compound that facilitates electron injection from the cathode or electron injection layer to the electron transport layer by improving the electron injection barrier, and further improves the electrical conductivity of the electron transport layer. Preferred examples of donor materials include alkali metals such as Li, inorganic salts containing alkali metals such as LiF, complexes of alkali metals and organic substances such as lithium quinolinol, alkaline earth metals, inorganic salts containing alkaline earth metals, complexes of alkaline earth metals and organic substances, rare earth metals such as Eu and Yb, inorganic salts containing rare earth metals, and complexes of rare earth metals and organic substances. Two or more of these may be used. Among these, metallic lithium, rare earth metals, and lithium quinolinol (Liq) are preferred.

[0124] (Charge generation layer) The charge generation layer in this invention is a layer that generates or separates charge by applying a voltage and injects the charge into an adjacent layer. The charge generation layer may be formed as a single layer or as multiple layers stacked together. Generally, layers that readily generate electrons as charge are called n-type charge generation layers, and layers that readily generate holes are called p-type charge generation layers. The charge generation layer preferably consists of a double layer, and a pn-junction type charge generation layer consisting of an n-type charge generation layer and a p-type charge generation layer is more preferable. In a light-emitting device, the pn-junction type charge generation layer generates charge or separates charge into holes and electrons by applying a voltage, and injects these holes and electrons into the light-emitting layer via a hole transport layer and an electron transport layer. Specifically, in a light-emitting device in which multiple light-emitting layers are stacked together, it functions as an intermediate charge generation layer. The n-type charge generation layer supplies electrons to the first light-emitting layer located on the anode side, and the p-type charge generation layer supplies holes to the second light-emitting layer located on the cathode side. Therefore, it is possible to further improve the device efficiency of a light-emitting element with multiple stacked light-emitting layers, reduce the driving voltage, and further improve the durability of the element.

[0125] The n-type charge generation layer consists of an n-type dopant and an n-type host, and conventional materials can be used for these. For example, as the n-type dopant, donor materials exemplified as materials for the electron transport layer are preferably used. Among these, alkali metals or their salts and rare earth metals are preferred, and metallic lithium, lithium fluoride (LiF), lithium quinolinol (Liq), and metallic ytterbium are more preferred. As the n-type host, materials exemplified as electron transport materials are preferably used. Among these, triazine derivatives, phenanthroline derivatives, and oligopyridine derivatives are preferred, phenanthroline derivatives and terpyridine derivatives are more preferred, and phenanthroline derivatives represented by the following general formula (3) are even more preferred. That is, the light-emitting element of the present invention preferably contains a phenanthroline derivative represented by general formula (3) in the charge generation layer.

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[0127] In the above general formula (3), Ar 1 The group is selected from the group consisting of p-valent aromatic hydrocarbon groups and p-valent aromatic heterocyclic groups. p is a natural number from 1 to 3. 8 ~R 15 These may be the same or different, and are selected from the group consisting of hydrogen atoms, alkyl groups, cycloalkyl groups, heterocyclic groups, aryl groups, and heteroaryl groups. 1 Of these, the substitution positions of the p phenantrolyl groups are arbitrary.

[0128] Examples of aromatic hydrocarbon groups include, in the case of monovalent groups, phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, benzofluorenyl, dibenzofluorenyl, phenanthryl, anthracenyl, benzophenanthryl, benzoanthracenyl, chrysenyl, pyrenyl, fluoranthenyl, triphenylenyl, benzofluoranthenyl, dibenzoanthracenyl, perilenyl, and hericenyl groups. Among these, from the viewpoint of ease of synthesis and sublimation, phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, phenanthryl, anthracenyl, pyrenyl, fluoranthenyl, triphenylenyl, and groups with at least one hydrogen atom removed are preferred. Aromatic hydrocarbon groups may or may not have substituents. The number of carbon atoms is not particularly limited, but is preferably in the range of 6 to 40, more preferably 6 to 30. Furthermore, if there are substituents on two adjacent carbon atoms, these substituents may form a ring structure.

[0129] A heterocyclic aromatic group refers to a cyclic aromatic group that has one or more atoms other than carbon in its ring. For example, in the monovalent case, these include pyridyl, furanyl, thiophenyl, quinolinyl, isoquinolinyl, pyrazinyl, pyrimidyl, pyridadinyl, triazinyl, naphthilidinyl, synnolinyl, phthalazinyl, quinoxalinyl, quinazolinyl, benzofuranyl, benzothiophenyl, indolyl, and dibenzofuranyl groups. Examples include the nyl group, dibenzothiophenyl group, carbazolyl group, benzocarbazolyl group, carbonyl group, indrocarbazolyl group, benzoflocarbazolyl group, benzothienocarbazolyl group, dihydroindenocarbazolyl group, benzoquinolinyl group, acridinyl group, dibenzoacridinyl group, benzimidazolyl group, imidazopyridyl group, benzoxazolyl group, benzothiazolyl group, and phenanthrolinyl group. However, the naphthilidinyl group refers to any of the 1,5-naphthilidinyl group, 1,6-naphthilidinyl group, 1,7-naphthilidinyl group, 1,8-naphthilidinyl group, 2,6-naphthilidinyl group, and 2,7-naphthilidinyl group. Aromatic heterocyclic groups may or may not have substituents. The number of carbon atoms in the aromatic heterocyclic group is not particularly limited, but is preferably in the range of 2 to 40, more preferably 2 to 30.

[0130] The aromatic hydrocarbon group or aromatic heterocyclic group may have further substituents in addition to the phenanthryl group.

[0131] From the viewpoint of sublimation properties and thin film formation properties, p is preferably 2.

[0132] An example of a phenanthroline derivative represented by general formula (3) is shown below.

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[0134] The above-mentioned p-type charge generation layer consists of a p-type dopant and a p-type host, and conventional materials can be used for these. For example, as the p-type dopant, acceptor materials exemplified as materials for the hole injection layer, as well as iodine, FeCl3, FeF3, and SbCl5 are preferably used. Specifically, examples include HAT-CN6, F4-TCNQ, tetracyanoquinodimethane derivatives, radialene derivatives, iodine, FeCl3, FeF3, and SbCl5. Among these, HAT-CN6 and radialene derivatives such as (2E,2'E,2''E)-2,2',2''-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)-acetonitrile) and (2E,2'E,2''E)-2,2',2''-(cyclopropane-1,2,3-triylidene)tris(2-(4-cyanoperfluorophenyl)-acetonitrile) are more preferred. A thin film of the p-type dopant may be formed, and its film thickness is preferably 10 nm or less. Furthermore, an arylamine derivative is preferred as the p-type host.

[0135] (electron injection layer) In the present invention, an electron injection layer may be provided between the cathode and the electron transport layer. It is preferable to have an electron injection layer and an electron transport layer between the cathode and the light-emitting layer, in this order from the cathode side. Generally, the electron injection layer is formed for the purpose of assisting the injection of electrons from the cathode to the electron transport layer. Examples of electron injection materials used in the electron injection layer include compounds having a heteroaryl ring structure containing electron-accepting nitrogen, and the donor materials mentioned above. Two or more of these may be included. Among these, triazine derivatives, phenanthroline derivatives, and oligopyridine derivatives are preferred, phenanthroline derivatives and terpyridine derivatives are more preferred, and phenanthroline derivatives represented by the general formula (3) are even more preferred. That is, it is preferable that the light-emitting element of the present invention contains a phenanthroline derivative represented by the general formula (3) in the electron injection layer.

[0136] Furthermore, inorganic materials such as insulators and semiconductors can be used in the electron injection layer. By using these materials, short circuits in the light-emitting element can be suppressed and electron injection performance can be improved.

[0137] Preferred insulators include metal compounds such as alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides, and alkaline earth metal halides. Two or more of these may be used.

[0138] (How to manufacture hibiscus) The formation method for each of the above-mentioned layers constituting the light-emitting element may be either a dry process or a wet process, and examples include resistance heating deposition, electron beam deposition, sputtering, molecular stacking, coating, inkjet, and printing. Among these, resistance heating deposition is preferred from the viewpoint of element characteristics.

[0139] The thickness of the organic layer cannot be limited as it depends on the resistance of the light-emitting material, but it is preferably 1 to 1000 nm. The film thickness of the light-emitting layer, electron transport layer, hole blocking layer, hole transport layer, electron blocking layer, and charge generation layer is preferably 1 nm to 200 nm, and more preferably 5 nm to 100 nm.

[0140] (Characteristics of light-emitting elements) The light-emitting element according to an embodiment of the present invention has the function of converting electrical energy into light. Here, DC current is mainly used as the electrical energy, but pulsed current or AC current can also be used. There are no particular restrictions on the current value and voltage value, and the required characteristic values ​​differ depending on the purpose of the element, but from the viewpoint of the power consumption and lifespan of the element, it is preferable to obtain high brightness at a low voltage.

[0141] In the light-emitting element according to the embodiment of the present invention, from the viewpoint of further improving color purity, the full width at half maximum in the fluorescence emission spectrum when current is applied is preferably 45 nm or less, more preferably 35 nm or less, and even more preferably 30 nm or less.

[0142] (Uses of light-emitting elements) The light-emitting element according to an embodiment of the present invention is suitably used as a display device, such as a display that displays in a matrix and / or segment format.

[0143] The light-emitting element according to the embodiment of the present invention is also preferably used as a backlight for various devices. Backlights are mainly used to improve the visibility of display devices such as non-self-illuminating displays, and are used in display devices such as liquid crystal displays, clocks, audio equipment, automobile panels, display boards, and signs. In particular, the light-emitting element of the present invention is preferably used as a backlight for liquid crystal displays, especially for PC applications where thinning is being considered, and can provide a backlight that is thinner and lighter than conventional ones.

[0144] The light-emitting element according to the embodiment of the present invention is also preferably used as various lighting devices. The light-emitting element according to the embodiment of the present invention can achieve both high element efficiency and high color purity, and furthermore, it can be made thinner and lighter, so a lighting device that combines low power consumption, vivid light emission color, and high design quality can be realized. [Examples]

[0145] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0146] First, the evaluation methods for each example and comparative example are described below.

[0147] ( 1 (H-NMR) The pyrometenboron complex obtained in Example 1 was subjected to deuterated chloroform solution using a superconducting FTNMR spectrometer EX-270 (manufactured by JEOL Ltd.). 1 The structure was identified by performing 1H-NMR measurements.

[0148] (Absorption spectrum) The pyrometenboron complex obtained in each example and comparative example was dissolved in toluene at a concentration of 10. -5For a mol / L diluted solution, the absorption spectrum was measured using a spectrophotometer (U-3010) manufactured by Hitachi High-Tech Science Co., Ltd., and the peak wavelength was determined.

[0149] (Emission spectrum) The pyrometenboron complex obtained in each example and comparative example was dissolved in toluene at a concentration of 10. -5 For a mol / L diluted solution, the emission spectrum was measured using a FluoroMax-4P fluorescence spectrophotometer manufactured by Horiba, Ltd., and the peak wavelength and full width at half maximum were determined.

[0150] (Fluorescence quantum yield) The pyrometenboron complex obtained in each example and comparative example was dissolved in toluene at a concentration of 10. -5 The fluorescence quantum yield (QY) of a mol / L diluted solution was measured using an absolute PL quantum yield analyzer manufactured by Hamamatsu Photonics K.K. The excitation wavelength was 460 nm.

[0151] (Ionization potential) The ionization potential Ip of the pyrometenboron complexes obtained in each example and comparative example was measured under air using a photoelectron spectrometer (RIKEN Keiki Co., Ltd.: AC-2).

[0152] (electron affinity) The pyrometenboron complexes obtained in each example and comparative example were deposited onto a quartz plate to create a 30 nm thick film. The absorption spectrum of the obtained film was measured using a spectrophotometer (U-3010) manufactured by Hitachi High-Tech Science Corporation. A tangent line was drawn to the falling edge on the long-wavelength side of the obtained absorption spectrum, and the wavelength value λ at the intersection of the tangent line and the horizontal axis was measured. edge The energy gap Eg was calculated by substituting [nm] into the following conversion formula 1. Conversion formula 1: Eg[eV]=1239.85 / λ edge The Ip-Eg value was calculated from the Ip and Eg values ​​measured or calculated using the method described above, and this was defined as the electron affinity Af, which was used as an index of the LUMO level.

[0153] (Thermally activated delayed fluorescence characteristics) The light-emitting element obtained in each example and comparative example had a current density of 0.1 mA / cm². 2 A voltage was applied to achieve the desired result, and the emission spectrum was measured using a Konica Minolta CS-1000 spectroradiometer. From the obtained emission spectrum, the external quantum efficiency (EQE) was calculated, assuming that lambassian emission occurred, and used as an indicator of the device efficiency.

[0154] Furthermore, the obtained light-emitting element has a current density of 10 mA / cm². 2 The emission spectrum was similarly measured when a voltage was applied in such a manner, and the peak wavelength and full width at half maximum were calculated.

[0155] (durability) The light-emitting element obtained in each example and comparative example had a current density of 10 mA / cm². 2 While applying a voltage to achieve this state, the brightness of the light-emitting element was measured using a photodiode, and the time it took for the brightness to reach 90% of the initial brightness (LT90) was measured and used as an indicator of durability.

[0156] The raw materials used in each example and comparative example will be described below.

[0157] Synthesis Example 1: Synthesis of Compound D-1 2.00 g of 2,4-dimethylpyrrole and anhydrous diethyl ether were placed in a flask and purged with nitrogen. The mixed solution was cooled to 0°C, and 12.9 mL of 1.6 M n-butyllithium was added dropwise, and the mixture was stirred at room temperature for 2 hours. 1.25 g of 2,6-dimethylaniline was added to the reaction solution and the mixture was stirred at room temperature for 30 minutes. 15.3 g of aldehyde in diethyl ether solution was added dropwise to the reaction solution and the mixture was stirred at 35°C for 3 hours. The reaction solution was cooled to room temperature, ammonium chloride solution was added and the mixture was stirred, and the organic layer was extracted. This organic layer was dried over magnesium sulfate, filtered, and the solvent was removed by distillation. The resulting reaction product was purified by silica gel chromatography to obtain 6.91 g of brown liquid D-1A.

[0158] 6.59 g of D-1A and 280 mL of toluene were placed in a flask and purged with nitrogen. 2.63 g of 3-ethyl-2,4-dimethylpyrrole was added to the reaction solution and purged with nitrogen again. 4.95 g of methanesulfonic anhydride was added to the reaction solution and heated and stirred at 80°C for 3 hours under a nitrogen stream. The reaction solution was cooled to room temperature, sodium bicarbonate solution was added and stirred, and the organic layer was extracted. This organic layer was dried over magnesium sulfate, filtered, and the solvent was removed by distillation to obtain D-1B.

[0159] 300 mL of toluene was added to D-1B in a flask and the mixture was purged with nitrogen. 12.6 mL of diisopropylethylamine was added and the mixture was stirred at room temperature for 15 minutes. 8.90 mL of boron trifluoride diethyl ether complex was added to the reaction solution and the mixture was stirred at room temperature for 15 hours. Water was then added and the mixture was stirred to extract the organic layer. This organic layer was dried over magnesium sulfate, filtered, and the solvent was removed by distillation. The resulting reaction product was purified by silica gel chromatography to obtain an orange powder. 40 mL of butyl acetate was added to the obtained powder and the mixture was heated and stirred at 140°C for 30 minutes, then allowed to cool. The precipitated solid was filtered and vacuum-dried to obtain 5.85 g of orange powder. 1 The results of the 1H-NMR analysis are as follows, confirming that the orange powder obtained above is compound D-1, which has a pyromethene skeleton. 1 H-NMR (CDCl3(d=ppm)): 7.95(s, 1H), 7.57(d, 4H), 7.52-7.51(m, 6H), 5.96(s, 1H), 2.57(s, 6H), 2.17(s, 6H), 1.48-1.37(m, 20H), 0.99(t, 3H).

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[0161] To further increase the purity, sublimation purification was performed. A metal container containing compound D-1 was placed inside a glass tube, and sublimation was induced by heating at 250°C under a pressure of 1 × 10⁻³ Pa using an oil diffusion pump. The solid adhering to the glass tube wall was collected and analyzed by LC-MS, revealing a purity of 99%.

[0162] The results of evaluating D-1 after sublimation purification using the method described above are shown below. Absorption spectrum (solvent: toluene): λmax 515nm Emission spectrum (solvent: toluene): λmax 532nm, FWHM 24nm Fluorescence quantum yield QY (solvent: toluene, excitation light: 460 nm): 89% Ionization potential: 5.72 eV Electron affinity: 3.46eV The structures of pyrometenboron complexes D-2 to D-10 used in each example and comparative example are shown below.

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[0164] The properties of pyrometenboron complexes D-1 to D-10 are shown in Table 1.

[0165] [Table 1]

[0166] The structures of the compounds used in the hole injection layer, hole transport layer, hole blocking layer, host material, TADF material, electron blocking layer, electron transport layer, charge generation layer, and electron injection layer in each example and comparative example are shown below.

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[0168] Example 1 A glass substrate (manufactured by Geomatec Co., Ltd., 11Ω / □, sputtered) with a 165nm ITO transparent conductive film deposited on it was cut to 38mm x 46mm and etched. The resulting substrate was ultrasonically cleaned for 15 minutes using "Semicoclean" (registered trademark) 56 (product name, manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water. Immediately before fabricating the device, this substrate was UV-ozone treated for 1 hour and placed in a vacuum deposition apparatus, where the vacuum level inside the apparatus was 5 x 10⁻⁶. -4 The system was evacuated until the pressure dropped below Pa. Using the resistance heating method, HAT-CN6 was first deposited as a hole injection layer at a thickness of 10 nm, followed by HT-1 as a hole transport layer at a thickness of 30 nm. Next, as an emissive layer, host material H-1, compound D-1, and TADF material compound H-2 were deposited to a thickness of 30 nm in a weight ratio of 79.0:1.0:20. Subsequently, ET-1 was deposited as a hole blocking layer at a thickness of 10 nm, and ET-2 as an electron transport layer at a thickness of 40 nm. Next, 2E-1 was deposited as an electron injection layer at a thickness of 0.5 nm, and then magnesium and silver were co-deposited at a thickness of 100 nm to form the cathode, creating a 5 mm × 5 mm square light-emitting device.

[0169] When the obtained light-emitting element was evaluated using the method described above, it was found to have an emission peak wavelength of 533 nm, a full width at half maximum of 24 nm, an external quantum efficiency of 15.3%, and an LT90 of 62 hours.

[0170] (Examples 2-8, Comparative Examples 1 and 2) A light-emitting element material and a light-emitting element were fabricated in the same manner as in Example 1, except that the compounds listed in Table 2 were used as the dopant material instead of pyrometenboron complex D-1. The evaluation results are shown in Table 2.

[0171] [Table 2]

[0172] Example 9 A glass substrate (manufactured by Geomatec Co., Ltd., 11Ω / □, sputtered) with a 165nm ITO transparent conductive film deposited on it was cut to 38mm x 46mm and etched. The resulting substrate was ultrasonically cleaned for 15 minutes using "Semicoclean" 56 (product name, manufactured by Furuuchi Chemical Co., Ltd.), and then rinsed with ultrapure water. Immediately before fabricating the device, this substrate was UV-ozone treated for 1 hour and placed in a vacuum deposition apparatus, where the vacuum level inside the apparatus was 5 x 10⁻⁶. -4 The atmosphere was evacuated until the pressure dropped below Pa. Using the resistance heating method, first, 5 nm of HAT-CN6 was deposited as a hole injection layer, followed by 50 nm of HT-1 as a hole transport layer. Next, 10 nm of H-1 was deposited as a hole blocking layer, and 20 nm of host material H-1 and compound D-1 were deposited as an emissive layer in a weight ratio of 99.5:0.5. Furthermore, 10 nm of ET-1 was deposited as an electron blocking layer, and 35 nm of compound ET-3 was deposited as an electron transport layer. Subsequently, 10 nm of n-type charge generation layer was deposited, consisting of n-type host compound ET-3 and n-type dopant metallic lithium, with a deposition rate ratio of 99:1. Furthermore, 10 nm of HAT-CN6 was deposited as a p-type charge generation layer. On top of this, a 50 nm hole transport layer, a 10 nm hole blocking layer, and a 20 nm emissive layer were formed in the same manner as above. Furthermore, ET-2 was deposited as an electron blocking layer at 10 nm, followed by ET-3 as an electron transport layer at 35 nm. Next, 2E-1 was deposited as an electron injection layer at 0.5 nm, and then magnesium and silver were co-deposited at 1000 nm to form the cathode, creating a tandem light-emitting element measuring 5 mm x 5 mm.

[0173] When the obtained light-emitting element was evaluated using the method described above, it showed an emission peak wavelength of 533 nm, a full width at half maximum of 24 nm, an external quantum efficiency of 7.9%, and an LT90 of 92 hours. Compared to Example 1, which had only one light-emitting layer, improved durability was confirmed.

Claims

1. A light-emitting element that emits light in response to electrical energy, having a light-emitting layer containing a pyrometenboron complex represented by the following general formula (1) between the anode and cathode. 【Chemistry 1】 (In the above general formula (1), R １ ~R ４ These may be the same or different, and each is independently selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. ５ and R ６ One of the groups is selected from the group consisting of substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted cycloalkenyl groups, substituted or unsubstituted alkynyl groups, hydroxyl groups, thiol groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted alkylthio groups, substituted or unsubstituted aryl ether groups, substituted or unsubstituted arylthioether groups, substituted or unsubstituted heterocyclic groups, substituted or unsubstituted amino groups, substituted or unsubstituted silyl groups, substituted or unsubstituted siloxanyl groups, and substituted or unsubstituted boryl groups, and the other is a hydrogen atom, substituted or unsubstituted A Selected from the group consisting of a lucyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted alkynyl group, a hydroxyl group, a thiol group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl ether group, a substituted or unsubstituted arylthioether group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siloxanyl group, and a substituted or unsubstituted boryl group. However, R ５ and R ６ These are different groups. X １ and X ２ These may be the same or different, and are selected from the group consisting of substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted aryloxy groups, hydroxyl groups, halogen atoms, and cyano groups. R ７ is selected from the group consisting of a substituted or unsubstituted aryl group and a substituted or unsubstituted heteroaryl group.)

2. R ５ and R ６ The light-emitting element according to claim 1, wherein one of the elements is selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups.

3. R ５ and R ６ The light-emitting element according to claim 2, wherein one of the elements is selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups, and the other element is hydrogen.

4. X １ and X ２ The light-emitting element according to any one of claims 1 to 3, which may be the same or different, and is selected from the group consisting of an alkyl group substituted with at least one halogen, an aryl group substituted with at least one halogen, an alkoxy group substituted with at least one halogen, an aryl ether group substituted with at least one halogen, a halogen atom, and a cyano group.

5. X １ and X ２ However, the light-emitting element according to claim 4 is a fluorine atom.

6. A light-emitting element according to any one of claims 1 to 5, having a peak wavelength of emission spectrum in the range of 500 nm to 550 nm.

7. The light-emitting element according to any one of claims 1 to 6, wherein the light-emitting layer has a first compound and a second compound which is a dopant, and the second compound is a pyrometenboron complex represented by the general formula (1).

8. The light-emitting element according to claim 7, wherein the first compound is a thermally activated delayed fluorescence compound.

9. The light-emitting element according to claim 8, wherein the light-emitting layer further comprises a third compound, and the singlet energy of the third compound is greater than the singlet energy of the first compound.

10. A light-emitting element according to any one of claims 1 to 9, having two or more light-emitting layers between an anode and a cathode, and one or more charge-generating layers between each of the light-emitting layers.

11. A light-emitting element according to any one of claims 1 to 10, wherein an electron injection layer and an electron transport layer are arranged between the cathode and the light-emitting layer in this order from the cathode side.

12. The light-emitting element according to claim 10, wherein the charge generation layer contains a phenanthroline derivative represented by the following general formula (3). 【Chemistry 2】 (Ar １ The group is selected from the group consisting of p-valent aromatic hydrocarbon groups and p-valent aromatic heterocyclic groups. p is a natural number from 1 to 3. R ８ ~R １５ These may be the same or different, and are selected from the group consisting of hydrogen atoms, alkyl groups, cycloalkyl groups, heterocyclic groups, aryl groups, and heteroaryl groups.

13. The light-emitting element according to claim 11, wherein the electron injection layer contains a phenanthroline derivative represented by the following general formula (3). 【Transformation 3】 (Ar 1 is selected from the group consisting of p-valent aromatic hydrocarbon groups and p-valent aromatic heterocyclic groups. p is a natural number from 1 to 3. R 8 to R 15 may be the same or different, and are selected from the group consisting of hydrogen atoms, alkyl groups, cycloalkyl groups, heterocyclic groups, aryl groups, and heteroaryl groups.)

14. The light-emitting element according to any one of claims 1 to 10, which is a top-emission type organic electroluminescent element.

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