Compound, light-emitting element including same, display device, electronic apparatus, and lighting device

Abstract

The present invention addresses the problem of providing a light-emitting element having excellent luminous efficiency and a highly durable lifespan.　This compound is represented by general formula (1). (In general formula (1), L is a substituted or unsubstituted arylene group or a substituted or unsubstituted heteroarylene group. However, when these groups are substituted, the substituent groups are alkyl groups or alkoxy groups. n is an integer of 2-5. In addition, at least one of the n Ls has a structure represented by general formula (2). A is a substituted or unsubstituted pyrimidyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted quinoxalinyl group, or a substituted or unsubstituted quinazolinyl group. However, when these groups have substituents, the substituents do not form a ring structure. B is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.) (In general formula (2), R1-R4 are each independently a hydrogen atom, an alkyl or an alkoxy group, and R1-R4 do not bond to each other to form a ring. * represents a bonding position with an adjacent substituent.)

Description

Compounds, light-emitting devices, display devices, electronic devices, and lighting devices containing the same.

[0001] The present invention relates to a compound, a light-emitting device, a display device, an electronic device, and a lighting device using the same.

[0002] Organic EL elements are light-emitting devices that have an anode, a cathode, and an organic layer interposed between them, and the organic layer emits light in response to electrical energy. In recent years, organic EL elements have been steadily put into practical use, such as being adopted in displays for televisions and smartphones. However, existing organic EL elements still have many technical challenges. In particular, achieving both high-efficiency light emission and a long lifespan for organic EL elements is a major challenge.

[0003] To address these challenges, compounds such as phenanthroline derivatives having specific electron-transport substituents (see, for example, Patent Documents 1-6) have been developed.

[0004] European Patent Application Publication No. 3333921, European Patent Application Publication No. 3263570, German Patent Application Publication No. 102023128819, Korean Registered Patent No. 102610656, Japanese Patent Publication No. 2004-281390, Korean Patent Application Publication No. 2018-0074176

[0005] According to the technologies described in Patent Documents 1 to 6, it is possible to obtain organic EL elements that have high luminous efficiency, can be driven at low voltage, and have excellent durability. However, in recent years, the luminous efficiency and durability required of organic EL elements have been increasing, and there is a need for technologies that can achieve both even higher luminous efficiency and long lifespan.

[0006] In view of the problems of the prior art, the present invention aims to provide a light-emitting element with excellent luminous efficiency and durability.

[0007] To solve the above problems, the present invention has the following configuration: [1] A compound represented by the following general formula (1).

[0008]

[0009] (In general formula (1), L is a substituted or unsubstituted arylene group or a substituted or unsubstituted heteroarylene group. However, if these groups are substituted, the substituents are alkyl or alkoxy groups. n is an integer from 2 to 5. Also, at least one of the n Ls is a structure represented by general formula (2). A is a substituted or unsubstituted pyrimidyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted quinoxalinyl group, or a substituted or unsubstituted quinazolinyl group. However, if these groups have substituents, the substituents do not form a ring structure. B is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.)

[0010]

[0011] (In general formula (2), R １ ~R ４ Each of these is independently a hydrogen atom, an alkyl group, or an alkoxy group, and R １ ~R ４ They do not bond to each other to form a ring. * indicates the bond position with an adjacent substituent.) [2] The compound according to [1], wherein B in the general formula (1) is a substituted or unsubstituted aryl group. [3] The compound according to [1] or [2], wherein L in the general formula (1) is a substituted or unsubstituted arylene group. [4] In the general formula (2), R １ ~R ４[1] to [3] above, wherein n is a hydrogen atom. [5] A compound according to any one of [1] to [4] above, in the general formula (1), n ​​is 2 or 3. [6] A light-emitting element that emits light by electrical energy, wherein at least an electron transport layer and a light-emitting layer are present between an anode and a cathode, and the electron transport layer contains a compound according to any one of [1] to [5]. [7] The light-emitting element according to [6] above, wherein the electron transport layer further contains an alkali metal atom, a rare earth metal atom, or an alkali metal complex compound. [8] The light-emitting element according to [7] above, wherein the electron transport layer contains an alkali metal atom, and the alkali metal atom is Li. [9] A light-emitting element that emits light by electrical energy, wherein at least a charge-generating layer and a light-emitting layer are present between an anode and a cathode, and the charge-generating layer contains a compound according to any one of [1] to [5].

[10] The light-emitting element according to [9] above, wherein the charge-generating layer further contains a phenanthroline derivative other than the general formula (1).

[11] The light-emitting element according to [9], wherein the charge generating layer further contains an alkali metal atom or a rare earth metal atom.

[12] The light-emitting element according to

[11] , wherein the charge generating layer contains an alkali metal atom, and the alkali metal atom is Li.

[13] The light-emitting element according to

[11] , wherein the charge generating layer contains a rare earth metal atom, and the rare earth metal atom is Yb.

[14] A light-emitting element that emits light by electrical energy, wherein at least an electron injection layer and a light-emitting layer are present between an anode and a cathode, and the electron injection layer contains a compound according to any one of [1] to [5].

[15] A display device comprising a light-emitting element containing a compound according to any one of [1] to [5].

[16] Electronic equipment comprising a light-emitting element containing a compound according to any one of [1] to [5].

[17] A lighting device comprising a light-emitting element containing a compound according to any one of [1] to [5].

[0012] The present invention makes it possible to provide a light-emitting element with excellent luminous efficiency and durability.

[0013] Hereinafter, preferred embodiments of the compound, light-emitting element, display device, electronic device, and lighting device of the present invention will be described in detail. However, the present invention is not limited to the following embodiments and can be variously modified and implemented according to the purpose and application.

[0014] (Compound represented by general formula (1)) The compound of the present invention is a compound represented by general formula (1).

[0015]

[0016] In general formula (1), L is a substituted or unsubstituted arylene group or a substituted or unsubstituted heteroarylene group. However, when these groups are substituted, the substituent is an alkyl group or an alkoxy group. n is an integer of 2 to 5. Also, at least one of the n Ls is a structure represented by general formula (2). A is a substituted or unsubstituted pyrimidyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted quinoxalinyl group, or a substituted or unsubstituted quinazolinyl group. However, when these groups have a substituent, the substituent does not form a ring structure. B is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

[0017]

[0018] In general formula (2), R １ ~R ４ are each independently a hydrogen atom, an alkyl group, or an alkoxy group, and R １ ~R ４ do not combine with each other to form a ring. * represents the bonding position with an adjacent substituent.

[0019] In all of the above groups, the hydrogen atom may be a deuterium atom. The same applies to the substituents, compounds, or partial structures described below.

[0020] In the case of "substituted or unsubstituted", "unsubstituted" means that a hydrogen atom or a deuterium atom is bonded. The same applies to the compounds or their partial structures described below in the case of "substituted or unsubstituted".

[0021] An aryl group means, for example, a monovalent aromatic hydrocarbon group such as a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthryl group, an anthracenyl group, a benzophenanthryl group, a benzoanthracenyl group, a chrysenyl group, a pyrenyl group, a fluoranthenyl group, a triphenylenyl group, a benzofluoranthenyl group, a dibenzoanthracenyl group, a perylenyl group, a helicenyl group, etc. The number of ring-forming atoms in the aryl group is not particularly limited, but is preferably 6 or more and 40 or less, more preferably 6 or more and 30 or less. Among these, a phenyl group is preferred.

[0022] An arylene group means, for example, a divalent aromatic hydrocarbon group such as a phenylene group, a biphenylene group, a terphenylene group, a naphthylene group, a fluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrylene group, an anthracenylene group, a benzophenanthrylene group, a benzoanthracenylene group, a chrysenylene group, a pyrenylene group, a fluoranthenylene group, a triphenyleneylene group, a benzofluoranthenylene group, a dibenzoanthracenylene group, a perylenylene group, a helicenylene group, etc. Here, the divalent bonds of the arylene group are attached to the same conjugated system. The number of ring-forming atoms in the arylene group is not particularly limited, but is preferably 6 or more and 40 or less, more preferably 6 or more and 30 or less. Among these, a phenylene group and a biphenylene group are preferred.

[0023] Heteroaryl groups include, for example, pyridyl, furanyl, thiophenyl, quinolinyl, isoquinolinyl, pyrazinyl, pyrimidyl, pyridadinyl, triazinyl, naphthilidinyl, synnolinyl, phthalazinyl, quinoxalinyl, quinazolinyl, benzofuranyl, benzothiophenyl, indolyl, dibenzofuranyl, dibenzothiophenyl, carbazolyl, and benzocarbazolyl groups. This refers to monovalent cyclic aromatic groups having one or more non-carbon atoms in the ring, such as a lyl group, carboninyl 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, naphthilidinyl group refers to any of 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 number of ring-forming atoms in the heteroaryl group is not particularly limited, but is preferably in the range of 5 to 40, more preferably 5 to 30. Among these, the pyridyl group is particularly preferred.

[0024] Heteroarylene groups include, for example, pyridylene, furanylene, thiophenylene, quinolinylene, isoquinolinylene, pyrazinylene, pyrimidylene, pyridadinylene, triazinylene, naphthylidine, sinolinylene, phthalazine, quinoxalinylene, quinazolinylene, benzofuranylene, benzothiophenylene, indolylene, dibenzofuranylene, dibenzothiophenylene, carbazoylene, and benzoca This refers to divalent cyclic aromatic groups having one or more non-carbon atoms in the ring, such as rubasolylene group, carbolinylene group, indrocarbazolylene group, benzoflocarbazolylene group, benzothienocarbazolylene group, dihydroindenocarbazolylene group, benzoquinolinylene group, acridinylene group, dibenzoacrydinylene group, benzimidazoylene group, imidazopyridylene group, benzooxazolylene group, benzothiazoylene group, and phenanthrolinylene group. However, naphthylidineylene group refers to any of the following: 1,5-naphthylidineylene group, 1,6-naphthylidineylene group, 1,7-naphthylidineylene group, 1,8-naphthylidineylene group, 2,6-naphthylidineylene group, and 2,7-naphthylidineylene group. Here, the divalent bonds of the heteroarylene group are attached to the same conjugated system. The number of ring-forming atoms in the heteroarylene group is not particularly limited, but is preferably in the range of 5 to 40, and more preferably 5 to 30.

[0025] Alkyl groups refer to saturated aliphatic hydrocarbon groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl groups. The number of carbon atoms in an alkyl group is not particularly limited, but from the standpoint of availability and cost, it is preferably in the range of 1 to 20, and more preferably 1 to 8. The number of carbon atoms referred to here includes the number of carbon atoms in substituents bonded to the alkyl group, and the same applies to other substituents that define the number of carbon atoms.

[0026] An alkoxy group refers to a group in which an alkyl group is bonded to oxygen, such as a methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, sec-butoxy group, or tert-butoxy group. The number of carbon atoms in an alkoxy group is not particularly limited, but from the standpoint of availability and cost, it is usually preferably between 1 and 20, and more preferably between 1 and 8.

[0027] As examples of conventional compounds containing electron-transporting substituents and phenanthroline skeletons, for instance, Patent Documents 1 to 6 show compounds represented by the following formulas.

[0028]

[0029] However, even when these compounds are used as materials for electron injection layers, electron transport layers, or charge generation layers in organic EL devices, they still do not provide sufficient performance to meet the characteristics required in recent years. Therefore, there is a need for compounds that can further improve performance in terms of luminous efficiency and durability.

[0030] For example, phenanthroline derivatives containing triazinyl groups, which are electron-transporting substituents, such as compounds U and V, have p-phenylene or m-phenylene groups as arylene groups linking phenanthroline and the triazinyl group. The phenanthroline skeleton and triazine ring are highly crystalline substituents, and compounds linked to them only by p-phenylene or m-phenylene groups have excessively high crystallinity due to the high planarity of the phenanthrolinyl group and the linking group, resulting in high driving voltages and problems with luminous efficiency and durability.

[0031] Phenanthroline derivatives like compound W, where the linking group between the triazinyl group and phenanthroline is only one phenylene group, cannot secure a sufficient conjugated system, leading to a decrease in electron mobility. This results in a high driving voltage, which poses challenges to luminescence efficiency and durability.

[0032] Compounds like compound X, which have bulky aromatic substituents on the linking group between the electron-transporting pyrimidinyl group and the phenanthrolinyl group, suffer from high operating voltages and challenges in luminous efficiency and durability due to their bulkiness, which significantly reduces the effect of improving intermolecular interactions.

[0033] Phenanthroline derivatives, such as compound Y, which have two phenanthroline skeletons, have low heat resistance and tend to generate impurities during deposition, so there has been a need to improve their heat resistance. In addition, due to their high crystallinity, they tend to crystallize in devices, which presents challenges in terms of drive voltage and durability.

[0034] Phenanthroline derivatives containing an acenaphthylpyrimidyl group, such as compound Z, lead to excessive crystallinity and an increase in sublimation temperature. Therefore, when attempting to deposit these with a metal to form a film, there are problems such as decreased film stability, increased driving voltage, and reduced luminescence efficiency and durability.

[0035] In their investigation of improvements, the inventors focused on the linking group between the phenanthrolinyl group and the electron-transporting substituent. In general formula (1), L is a substituted or unsubstituted arylene group or a substituted or unsubstituted heteroarylene group. When L is substituted, the substituent is an alkyl group or an alkoxy group. These substituents are preferred because they can improve the stability of the compound without reducing the charge transport properties of the compound.

[0036] Furthermore, at least one of the n L groups has the structure represented by general formula (2). Because at least one of the linking groups has the structure represented by general formula (2), the bond positions of the two units flanking that linking group are adjacent to each other. Having such a structure strengthens the steric hindrance between molecules, thus suppressing excessive crystallinity. Therefore, when used in organic EL devices, the driving voltage can be reduced and the luminous efficiency can be improved.

[0037] In general formula (1), A is a substituted or unsubstituted pyrimidyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted quinoxalinyl group, or a substituted or unsubstituted quinazolinyl group. These substituents have excellent electron transport properties, which can reduce the driving voltage when used in organic EL devices and improve luminous efficiency and durability. From the viewpoint of suppressing excessive crystallinity of the compound, when these groups have substituents, the substituents do not form a ring structure. From the viewpoint of further improving driving voltage, luminous efficiency, and durability, A is preferably a substituted or unsubstituted pyrimidyl group or a substituted or unsubstituted triazinyl group, and more preferably a substituted or unsubstituted triazinyl group.

[0038] In general formula (1), B is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. From the viewpoint of further improving the stability and lifespan of the device, a substituted or unsubstituted aryl group is preferred for B.

[0039] In general formula (1), it is preferable that L is a substituted or unsubstituted arylene group from the viewpoint of improving film stability and further improving driving voltage, luminous efficiency, and durability life.

[0040] In general formula (2), R is used to further improve the stability and lifespan of the element. １ ~R ４ A hydrogen atom is preferred.

[0041] In general formula (1), n ​​is preferably 2 or 3 from the viewpoint of the sublimation properties and heat resistance of the material.

[0042] The molecular weight of the compound represented by general formula (1) is preferably 450 or more, and more preferably 470 or more, from the viewpoint of suppressing crystallization and improving the stability of the film. On the other hand, from the viewpoint of improving processability during sublimation purification and vapor deposition, the molecular weight of the compound represented by general formula (1) is preferably 750 or less.

[0043] Examples of compounds represented by general formula (1) include the compounds listed below. Note that these are examples only, and any compound represented by general formula (1) other than those specified herein may be similarly preferred.

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] Compounds represented by general formula (1) can be synthesized by known synthetic methods. Examples of such methods include, but are not limited to, coupling reactions between phenanthroline derivatives and electron-transport substituents.

[0080] The compound represented by general formula (1) is preferably used in any layer of the light-emitting element. As described later, the compound represented by general formula (1) is suitably used in hole injection layers, hole transport layers, light-emitting layers, electron transport layers, charge generation layers, electron injection layers, electrode protective films (cap layers), etc., in the light-emitting element. By using the material represented by general formula (1) in any layer of the light-emitting element, a light-emitting element with excellent luminous efficiency and durability can be provided.

[0081] (Light-emitting element) The light-emitting element of the present invention has an anode and a cathode, and an organic layer interposed between the anode and cathode, and the organic layer emits light in response to electrical energy. Such a light-emitting element may be referred to as an "organic EL element" in this specification.

[0082] In organic EL devices, the layer configuration between the anode and cathode can be a stacked configuration consisting of only an emissive layer, as well as the following: 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, and 7) hole injection layer / hole transport layer / emissive layer / hole blocking layer / electron transport layer / electron injection layer.

[0083] Furthermore, the above-mentioned laminated configuration may be a tandem type in which multiple layers are stacked with an intermediate layer in between. The intermediate layer is generally also called an intermediate electrode, intermediate conductive layer, charge generation layer, electron extraction layer, connecting layer, or intermediate insulating layer, and known layer configurations can be used. Specific examples of the tandem type include, for example, 8) hole transport layer / light-emitting layer / electron transport layer / charge generation layer / hole transport layer / light-emitting layer / electron transport layer, and 9) 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 include a charge generation layer as an intermediate layer between the anode and cathode.

[0084] Furthermore, each of the above layers may be a single layer or multiple layers, and may be doped. In particular, the electron injection layer, electron transport layer, and charge generation layer are preferably metal-doped layers, which can improve electron transport capability and electron injection capability to adjacent layers. In addition, a protective layer (cap layer) may be further included in addition to the above layers, which can further improve luminescence efficiency through optical interference effects.

[0085] The compound represented by general formula (1) may be used in any of the above layers in an organic EL element, but is particularly suitable for use in an electron transport layer, a charge generation layer, or an electron injection layer. Preferred configurations of the light-emitting element of the present invention include: a configuration having at least an electron transport layer and a light-emitting layer between the anode and the cathode, with the electron transport layer containing the compound represented by general formula (1); a configuration having at least a charge generation layer and a light-emitting layer between the anode and the cathode, with the charge generation layer containing the compound represented by general formula (1); and a configuration having at least an electron injection layer and a light-emitting layer between the anode and the cathode, with the electron injection layer containing the compound represented by general formula (1). In these cases, two or more compounds represented by general formula (1) may be included.

[0086] In the light-emitting element of the present invention, the anode and cathode serve to supply the current necessary for the element to emit light, and it is desirable that at least one of them be transparent or semi-transparent in order to extract light.

[0087] (Substrate) To maintain the mechanical strength of the organic EL element, it is preferable to form the organic EL element on a substrate. Examples of substrates include glass substrates such as soda glass or alkali-free glass, and plastic substrates. The thickness of the glass substrate should be sufficient to maintain mechanical strength, and 0.5 mm or more is sufficient. Regarding the glass material, it is preferable that there are few ions eluted from the glass, and alkali-free glass is preferred. Also, SiO ２ Soda-lime glass with barrier coatings such as those mentioned above is also commercially available and can be used.

[0088] (Anode) The material used for the anode is preferably a substance that can efficiently implant holes into the organic layer. It is also preferably transparent or translucent in order to extract light. Examples of such substances include conductive metal oxides such as zinc oxide, tin oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO), as well as metals such as gold, silver, and chromium, inorganic conductive substances such as copper iodide and copper sulfide, and conductive polymers such as polythiophene, polypyrrole, and polyaniline. Among these, ITO glass and NESA glass are preferred. These substances may be used individually or in combination. When multiple substances are used in combination, multiple layers composed of different substances may be laminated together, or the layer may be composed of a material mixed with multiple substances.

[0089] (Cathode) The material used for the cathode is preferably a substance that can efficiently inject electrons into the organic layer. Furthermore, if the organic EL element has a top-emission structure that extracts light from the cathode side, it is preferable that the material be transparent or translucent. Examples of materials that can be used for the cathode include metals such as platinum, gold, silver, copper, iron, tin, aluminum, and indium, or alloys or multilayers of these metals with low work function metals such as lithium, sodium, potassium, calcium, and magnesium, or conductive metal oxides such as ITO and IZO. Among these, aluminum, silver, and magnesium are preferred as the main components in terms of electrical resistance, ease of film formation, film stability, and luminous efficiency, and it is more preferable that the electrode is composed of magnesium and silver because it facilitates electron injection into the electron transport layer and electron injection layer. In the case of a top-emission structure, a translucent electrode composed of magnesium and silver and IZO are preferred.

[0090] (Protective Layer) To protect the cathode, it is preferable to laminate a protective layer (capping layer) on the cathode. The material used to constitute the protective layer (capping material) 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. Compounds represented by general formula (1) can also be used as capping materials. However, if the organic EL element has a top emission structure that extracts light from the cathode side, it is preferable that the capping material has light transmittance in the visible light region. It is also possible to use a single layer made up of multiple materials used for the cathode and protective layer, and use one of these layers as the cathode.

[0091] (Hole Injection Layer) The hole injection layer is a layer placed between the anode and the hole transport layer. 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 is preferable because it allows for lower voltage operation, improves durability and lifespan, and further improves the carrier balance of the device, thereby improving luminous efficiency.

[0092] The materials constituting the hole injection layer are known materials. Hereafter, the materials constituting the hole injection layer may be abbreviated as hole injection materials. Examples of substances used as hole injection materials include benzidine derivatives, a group of compounds called starburst arylamines, triarylamine derivatives, biscarbazole derivatives, pyrazoline derivatives, stilbene compounds, fluorene compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxadiazole derivatives, phthalocyanine derivatives, heterocyclic compounds such as porphyrin derivatives, polycarbonates and styrene derivatives having the aforementioned derivatives or compounds in their side chains, and polymers such as polythiophene, polyaniline, polyfluorene, polyvinylcarbazole, and polysilane. From the viewpoint of smoothly injecting and transporting holes from the anode to the hole transport layer, benzidine derivatives, the starburst arylamine group of compounds, and fluorene compounds are more preferably used.

[0093] These materials may be used individually or in combination of two or more. Layers composed of these multiple hole-injection materials may be stacked to form a hole-injection layer.

[0094] Furthermore, preferred embodiments of the hole injection layer include an embodiment in which the hole injection layer is composed solely of the acceptor compound described later, or an embodiment in which the hole injection layer is composed of the above-mentioned hole injection material doped with the acceptor compound described later. By adopting these embodiments, it is possible to drive at the lower voltage described above, which not only improves the durability life but also more significantly improves the carrier balance of the device and thus improves the luminous efficiency, making them more preferable. Here, the acceptor compound is a compound that forms a charge transfer complex with the substance constituting the hole transport layer in contact with it when used as a single layer film, and with the substance used in the hole injection material when used as a dopant. By using such an acceptor compound, the conductivity of the hole injection layer is improved, which contributes to further reducing the driving voltage of the device and further improves the luminous efficiency and durability life.

[0095] Known compounds can be used as acceptor compounds. Examples include metal chlorides, metal oxides such as molybdenum oxide, charge transfer complexes, organic compounds having a nitro group, cyano group, halogen or trifluoromethyl group in the molecule, quinone compounds, acid anhydride compounds, and fullerenes. Among these, metal oxides and cyano group-containing compounds are preferred because they are easy to handle and can be easily deposited, thus easily obtaining the effects described above. Whether the hole injection layer is composed of an acceptor compound alone or the acceptor compound is doped into a substance used as a hole injection material, the hole injection layer may be a single layer or may be composed of multiple layers stacked together.

[0096] (Hole Transport Layer) The hole transport layer is the layer that transports holes injected from the anode to the light-emitting layer. The hole transport layer can be a single layer or composed of multiple layers stacked together.

[0097] Examples of materials used in the hole transport layer include those exemplified for use in the hole injection layer. When the hole transport layer plays a role in improving the hole injection efficiency from the material used in the anode, it is specifically called a hole injection layer, and in a broad sense, the hole injection layer is also included in the hole transport layer. From the viewpoint of smoothly injecting and transporting holes to the light-emitting layer, triarylamine derivatives or benzidine derivatives are more preferred.

[0098] (Emitting Layer) The emissive layer may be a single layer or multiple layers. The emissive layer is formed of an emissive material, which may be a mixture of a host material and a dopant material, a host material alone, or a mixture of two types of host materials and one type of dopant material. In other words, in the light-emitting element of the present invention, in each emissive layer, only the host material or the dopant material may emit light, or both the host material and the dopant material may emit light. From the viewpoint of efficiently utilizing electrical energy and obtaining high color purity emission, it is preferable that the emissive layer consists of a mixture of a host material and a dopant material. Furthermore, the host material and the dopant material may each be one type or a combination of multiple types. The dopant material may be contained throughout the host material or partially contained within it. The dopant material may be laminated or dispersed. The emission color can be controlled by selecting the dopant material. From the viewpoint of suppressing the concentration quenching phenomenon, the amount of dopant material is preferably 30% by weight or less relative to the host material, and more preferably 20% by weight or less. The doping method can be achieved by co-deposition with the host material, or by pre-mixing with the host material and then simultaneously depositing the doping material.

[0099] Known compounds can be used as luminescent materials. Examples include condensed ring derivatives such as anthracene and pyrene, which are known to be luminescent; metal chelated oxynoide compounds such as tris(8-quinolinolate)aluminum; bisstyryl derivatives such as bisstyrylanthracene derivatives and distylylbenzene derivatives; tetraphenylbutadiene derivatives; indene derivatives; coumarin derivatives; oxadiazole derivatives; pyrrolopyridine derivatives; perinone derivatives; cyclopentadiene derivatives; oxadiazole derivatives; thiadiazolopyridine derivatives; dibenzofuran derivatives; carbazole derivatives; indrocarbazole derivatives; and polymers such as polyphenylenevinylene derivatives, polyparaphenylene derivatives, and polythiophene derivatives.

[0100] The host material contained in the luminescent material is not limited to just one compound; multiple compounds may be mixed and used. They may also be used in a layered configuration. Known compounds can be used as the host material. While not particularly limited, these include compounds having condensed aryl rings such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, perylene, fluorantene, fluorene, and indene, as well as their derivatives; aromatic amine derivatives such as N,N'-dinaphthyl-N,N'-diphenyl-4,4'-diphenyl-1,1'-diamine; metal chelated oxynoide compounds such as tris(8-quinolinate)aluminum(III); and bisstyryl derivatives such as distylylbenzene derivatives. Examples of polymers include tetraphenylbutadiene derivatives, indene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, pyrrolopyrrole derivatives, thiadiazolopyridine derivatives, dibenzofuran derivatives, carbazole derivatives, indolocarbazole derivatives, triazine derivatives, and polymers such as polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, and polythiophene derivatives. Among these, metal chelated oxynoide compounds, dibenzofuran derivatives, dibenzothiophene derivatives, carbazole derivatives, indolocarbazole derivatives, triazine derivatives, and triphenylene derivatives are preferably used as host materials when the luminescent layer performs triplet emission (phosphorescence).

[0101] Compounds used as dopant materials contained in luminescent materials include, for example, compounds having an aryl ring and its derivatives, compounds having a heteroaryl ring and its derivatives, distyrylbenzene derivatives, aminostyryl derivatives, aromatic acetylene derivatives, tetraphenylbutadiene derivatives, stilbene derivatives, aldazine derivatives, pyromethene derivatives, diketopyrrolo[3,4-c]pyrrole derivatives, coumarin derivatives, azole derivatives, their metal complexes, aromatic amine derivatives, and compounds represented by the following general formula (3). Among these, dopant materials containing a diamine skeleton and dopant materials containing a fluorantene skeleton can further improve luminescence efficiency, and compounds represented by the following general formula (3) can further improve luminescence efficiency and durability.

[0102]

[0103] In general formula (3), the Za ring, Zb ring, and Zc ring are each independently a substituted or unsubstituted aryl ring having 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl ring having 5 to 30 ring-forming atoms. １ and Z ２ These are, independently, an oxygen atom, an NRa (a nitrogen atom with a substituent Ra), or a sulfur atom. １ If is NRa, the substituent Ra may or may not bond to the Za ring or Zb ring to form a ring, and Z ２ If is NRa, the substituent Ra may or may not bond to the Zb or Zc ring to form a ring. １ and Z ２ When all of them are NRa, Ra is preferably independently a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, a substituted or unsubstituted heteroaryl group having 5 to 30 ring-forming atoms, or a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms. In general formula (3), Z １ and Z ２All of these are NRa, and Ra is preferably a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms. In general formula (3), Y is a boron atom, a phosphorus atom, SiRb (a silicon atom having a substituent Rb), P=O, or P=S. Rb is independently a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, a substituted or unsubstituted heteroaryl group having 5 to 30 ring-forming atoms, or a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms. Y is preferably a boron atom. In general formula (3), when Ra, Rb, and all of the Za-Zc rings are substituted, preferred substituents are alkyl groups, cycloalkyl groups, heteroalicyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, hydroxyl groups, thiol groups, alkoxy groups, alkylthio groups, aryl ether groups, arylthioether groups, halogens, cyano groups, aldehyde groups, acyl groups, carboxyl groups, ester groups, amide groups, acyl groups, sulfonyl groups, sulfonic acid ester groups, sulfonamide groups, amino groups, nitro groups, silyl groups, siloxanyl groups, boryl groups, and oxo groups. Furthermore, these substituents may be further substituted with the substituents described above.

[0104] Examples of alkyl groups, alkoxy groups, aryl groups, and heteroaryl groups include those exemplified as substituents in general formula (1).

[0105] 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 ring-forming carbon atoms is not particularly limited, but is preferably in the range of 3 to 20.

[0106] A heteroalicyclic group refers to an aliphatic ring having atoms other than carbon within the ring, such as a pyran ring, a piperidine ring, or a cyclic amide, which may or may not have substituents. The number of ring-forming atoms is not particularly limited, but is preferably in the range of 3 to 20.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] An alkylthio group is a group in which the oxygen atom in the ether bond of an alkoxy group is replaced by a sulfur atom. Alkylthio groups may or may not have substituents. The number of carbon atoms in an alkylthio group is not particularly limited, but is preferably in the range of 1 to 20.

[0111] 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 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.

[0112] An arylthioether group refers to a functional group in which the oxygen atom of the ether bond of an aryl ether group is replaced by a sulfur atom, and 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.

[0113] Halogens refer to fluorine, chlorine, bromine, or iodine.

[0114] An acyl group refers to a functional group in which an alkyl group, cycloalkyl group, alkenyl group, alkynyl group, aryl group, or heteroaryl group is bonded via a carbonyl group, such as an acetyl group, propionyl group, benzoyl group, or acryl group, and may or may not have substituents. The number of carbon atoms in the acyl group is not particularly limited, but is preferably 2 to 40, more preferably 2 to 30.

[0115] An ester group refers to a functional group formed by linking alkyl groups, cycloalkyl groups, aryl groups, heteroaryl groups, etc., via an ester bond, and may or may not have substituents. The number of carbon atoms in the ester group is not particularly limited, but is preferably in the range of 1 to 20. More specifically, examples include methyl ester groups such as methoxycarbonyl groups, ethyl ester groups such as ethoxycarbonyl groups, propyl ester groups such as propoxycarbonyl groups, butyl ester groups such as butoxycarbonyl groups, isopropyl ester groups such as isopropoxymethoxycarbonyl groups, hexyl ester groups such as hexyloxycarbonyl groups, and phenyl ester groups such as phenoxycarbonyl groups.

[0116] An amide group refers to a functional group formed by linking alkyl groups, cycloalkyl groups, aryl groups, heteroaryl groups, etc., via an amide bond, and may or may not have substituents. The number of carbon atoms in an amide group is not particularly limited, but is preferably in the range of 1 to 20. More specifically, examples include methylamide group, ethylamide group, propylamide group, butylamide group, isopropylamide group, hexylamide group, and phenylamide group.

[0117] Sulfonyl groups include, for example, alkyl groups, cycloalkyl groups, aryl groups, and heteroaryl groups, which have the -S (=O) property. ２ - Indicates a functional group bonded via a bond, and may or may not have substituents. The number of carbon atoms in the sulfonyl group is not particularly limited, but is preferably in the range of 1 to 20.

[0118] A sulfonic acid ester group refers to a functional group in which an alkyl group, cycloalkyl group, aryl group, heteroaryl group, etc., is linked via a sulfonic acid ester bond, and may or may not have substituents. Here, a sulfonic acid ester bond is a bond in which the carbonyl portion of the ester bond, i.e., -C(=O)-, is replaced by a sulfonyl portion, i.e., -S(=O). ２ This refers to a group that has been substituted with a negative sign. The number of carbon atoms in the sulfonic acid ester group is not particularly limited, but is preferably in the range of 1 to 20.

[0119] A sulfonamide group refers to a functional group in which an alkyl group, cycloalkyl group, aryl group, heteroaryl group, etc., is bonded via a sulfonamide bond, and may or may not have substituents. Here, a sulfonamide bond is defined as the carbonyl portion of an amide bond, i.e., -C(=O)-, being a sulfonyl portion, i.e., -S(=O) ２ This refers to a group that has been substituted with a negative sign. The number of carbon atoms in the sulfonamide group is not particularly limited, but is preferably in the range of 1 to 20.

[0120] The amino group may or may not have substituents. The number of carbon atoms in the amino group 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.

[0121] 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 silyl group may or may not have substituents. The number of carbon atoms in the silyl group is not particularly limited, but is preferably in the range of 1 to 30.

[0122] A siloxanyl group refers to a silicon compound group via an ether bond, such as a trimethylsiloxanyl group. The siloxanyl group may or may not have substituents.

[0123] The boryl group may or may not have substituents.

[0124] Examples of compounds represented by general formula (3) include the following:

[0125]

[0126] The light-emitting element of the present invention may also preferably contain a triplet light-emitting material in its light-emitting layer.

[0127] When the light-emitting layer performs triplet emission (phosphorescence), the dopant material used is preferably 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). The ligand constituting the metal complex compound preferably has a nitrogen-containing aromatic heterocycle such as a phenylpyridine skeleton, a phenylquinoline skeleton, or a carbene skeleton. However, it is not limited to these, and an appropriate complex is selected based on the required emission color, device performance, and relationship with the host material.

[0128] Specific examples of metal complex compounds include tris(2-phenylpyridyl)iridium complex, tris{2-(2-thiophenyl)pyridyl}iridium complex, tris{2-(2-benzothiophenyl)pyridyl}iridium complex, tris(2-phenylbenzothiazole)iridium complex, tris(2-phenylbenzoxazole)iridium complex, trisbenzoquinolineiridium complex, bis(2-phenylpyridyl)(acetylacetonate)iridium complex, bis{2-(2-thiophenyl)pyridyl}iridium complex, bis{2-(2-benzothiophenyl)pyridyl}(acetylacetonate)iridium complex, bis(2-phenylbenzothiazole)(acetylacetonate)iridium complex, Examples include bis(2-phenylbenzoxazole)(acetylacetonate)iridium complex, bisbenzoquinoline(acetylacetonate)iridium complex, bis{2-(2,4-difluorophenyl)pyridyl}(acetylacetonate)iridium complex, tetraethylporphyrin platinum complex, {tris(senoyltrifluoroacetone)mono(1,10-phenanthroline)}europium complex, {tris(senoyltrifluoroacetone)mono(4,7-diphenyl-1,10-phenanthroline)}europium complex, {tris(1,3-diphenyl-1,3-propanedione)mono(1,10-phenanthroline)}europium complex, and trisacetylacetone terbium complex. In addition, phosphorescent dopant materials described in Japanese Patent Application Publication No. 2009-130141 are also suitably used. Iridium complexes or platinum complexes are preferred, as they can further improve luminescence efficiency.

[0129] The triplet luminescent materials used as dopant materials may consist of only one type in the luminescent layer, or they may be mixed together in a mixture of two or more types. When two or more triplet luminescent materials are included, the total weight of the dopant materials is preferably 30% by weight or less, and more preferably 20% by weight or less, relative to the host material.

[0130] The compounds used as preferred host materials in triplet emission systems are not particularly limited, but specific examples include the following.

[0131]

[0132] The compounds used as preferred dopant materials in triplet emission systems are not particularly limited, but specific examples include the following.

[0133]

[0134] Furthermore, it is preferable that the light-emitting layer contains a thermally activated delayed fluorescence material. Thermally activated delayed fluorescence is explained on pages 87-103 of "Cutting-Edge Organic EL" (edited by Chihaya Adachi and Hiroshi Fujimoto, published by CMC Publishing). In that document, it is explained that by bringing the energy levels of the excited singlet state and the excited triplet state of the fluorescent light-emitting material close together, the reverse energy transfer from the excited triplet state to the excited singlet state, which normally has a low transition probability, occurs with high efficiency, and thermally activated delayed fluorescence (TADF) is expressed. Furthermore, the mechanism of delayed fluorescence generation is explained in Figure 5 of the same document. The emission of delayed fluorescence can be confirmed by transient PL (PhotoLuminescence) measurement.

[0135] Thermally activated delayed fluorescence (TADF) materials are also commonly referred to as TADF materials. A thermally activated delayed fluorescence material may exhibit thermal activation delayed fluorescence as a single compound, or it may exhibit thermal activation delayed fluorescence by combining multiple compounds. When the material is composed of multiple compounds, a mixture containing the multiple compounds may be used as the thermally activated delayed fluorescence material, or layers containing each compound may be laminated and used. Known compounds can be used as thermally activated delayed fluorescence materials. Examples include, but are not limited to, benzonitrile derivatives, triazine derivatives, disulfoxide derivatives, carbazole derivatives, indolocarbazole derivatives, dihydrophenazine derivatives, thiazole derivatives, and oxadiazole derivatives.

[0136] In devices where the light-emitting layer contains TADF material, it is preferable that the light-emitting layer also contains a dopant material used for singlet emission. This is because the TADF material converts triplet excitons into singlet excitons, and the dopant material used for singlet emission receives these singlet excitons, thereby achieving higher luminescence efficiency and a longer lifespan.

[0137] (Electron Transport Layer) In the present invention, the electron transport layer is a layer that receives electrons from the cathode and transports them. It is desirable for the electron transport layer to have high electron injection efficiency and to efficiently transport the injected electrons. For this reason, the material constituting the electron transport layer is preferably a substance that has high electron affinity, high electron mobility, excellent stability, and does not easily generate trapping impurities during manufacturing and use. In particular, when stacking thick films, low molecular weight compounds tend to crystallize and degrade the film quality, so a compound with a molecular weight of 400 or more is preferred in order to maintain a stable film quality. However, when considering the balance between hole and electron transport, if the electron transport layer mainly plays the role of efficiently preventing holes from the anode from flowing to the cathode side without recombining, then even if it is composed of a material with not very high electron transport capability, the effect of improving luminescence efficiency will be the same as if it were composed of a material with high electron transport capability. Therefore, the electron transport layer in the present invention also includes a hole blocking layer that can efficiently block the movement of holes. The electron transport layer may be composed of a single material or of multiple materials stacked together.

[0138] Known compounds can be used as electron transport materials in the electron transport layer. Examples include condensed polycyclic aromatic derivatives, styryl aromatic ring derivatives, quinone derivatives, phosphorus oxide derivatives, quinolinol complexes, benzoquinolinol complexes, hydroxyazole complexes, azomethine complexes, tropolone metal complexes, and various metal complexes such as flavonol metal complexes. It is preferable to use compounds that are composed of elements selected from carbon, hydrogen, nitrogen, oxygen, silicon, and phosphorus, and have a heteroaryl ring structure containing electron-accepting nitrogen, in order to further reduce the driving voltage and obtain more efficient light emission.

[0139] In this context, electron-accepting nitrogen refers to nitrogen atoms that form multiple bonds with adjacent atoms. Because nitrogen atoms have high electronegativity, these multiple bonds possess electron-accepting properties. Therefore, aromatic heterocycles containing electron-accepting nitrogen have high electron affinity. Electron transport materials containing electron-accepting nitrogen readily accept electrons from cathodes with high electron affinity, enabling operation at lower voltages. Furthermore, the increased supply of electrons to the light-emitting layer and the higher recombination probability lead to improved luminescence efficiency.

[0140] Examples of heteroaryl rings containing electron-accepting nitrogen include triazine rings, pyridine rings, pyrazine rings, pyrimidine rings, quinoline rings, quinoxaline rings, quinazoline rings, naphthyridine rings, pyrimidopyrimidine rings, benzoquinoline rings, phenanthroline rings, imidazole rings, oxazole rings, oxadiazole rings, triazole rings, thiazole rings, thiadiazole rings, benzoxazole rings, benzothiazole rings, benzimidazole rings, and phenanthroimidazole rings.

[0141] Examples of compounds having these heteroaryl ring structures include pyridine derivatives, bipyridine derivatives, terpyridine derivatives, triazine derivatives, quinazoline derivatives, pyrimidine derivatives, benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, triazole derivatives, pyrazine derivatives, phenanthroline derivatives, quinoxaline derivatives, quinoline derivatives, benzoquinoline derivatives, oligopyridine derivatives, quinoxaline derivatives, and naphthiridine derivatives. Among these, benzimidazole derivatives, oxadiazole derivatives, triazole derivatives, triazine derivatives, pyrimidine derivatives, phenanthroline derivatives, benzoquinoline derivatives, bipyridine derivatives, terpyridine derivatives, and naphthiridine derivatives are preferred from the viewpoint of electron transport ability.

[0142] Furthermore, it is preferable that these derivatives have a condensed polycyclic aromatic skeleton, as this improves the glass transition temperature and increases electron mobility, allowing for a further reduction in the driving voltage of the organic EL device. Moreover, considering the improved durability life of the device, ease of synthesis, and availability of raw materials, it is even more preferable that the condensed polycyclic aromatic skeleton be a fluorantene skeleton, anthracene skeleton, pyrene skeleton, or phenanthroline skeleton.

[0143] The compounds used as preferred electron transport materials are not particularly limited, but specific examples include the following:

[0144]

[0145]

[0146] Furthermore, compounds represented by general formula (1) are also preferred because they possess high electron transport properties and exhibit excellent properties as materials for electron transport layers.

[0147] The above-mentioned electron transport materials may be used alone, or two or more of the above-mentioned electron transport materials may be used in combination, or one or more other electron transport materials may be used in combination with the above-mentioned electron transport materials.

[0148] The electron transport layer may contain a donor material. Here, the 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.

[0149] The material used as the donor material preferably contains alkali metal atoms, alkaline earth metal atoms, or rare earth metal atoms from the viewpoint of low work function and improved electron transport properties. In particular, from the viewpoint of further reducing the driving voltage of the organic EL, it is more preferable to contain alkali metal atoms, rare earth metal atoms, or copper group atoms, alkali metal atoms are even more preferable, and Li atoms are particularly preferable.

[0150] Furthermore, because deposition in a vacuum is easy and handling is excellent, the donor material is preferably in the form of an inorganic salt or a complex of a metal and an organic substance rather than a single metal. Moreover, it is even more preferable to be in the form of a complex of a metal and an organic substance because it facilitates handling in air and allows for easy adjustment of the additive concentration. Examples of inorganic salts include oxides, nitrides, fluorides, and carbonates. Preferred examples of organic substances in complexes with organic substances include quinolinol, benzoquinolinol, pyridylphenol, flavonol, hydroxyimidazopyridine, hydroxybenzazole, and hydroxytriazole. Among these, complexes of alkali metals and organic substances are preferred from the viewpoint of further reducing the driving voltage of the organic EL element. Furthermore, from the viewpoint of ease of synthesis and thermal stability, complexes of lithium and organic substances are even more preferred, and lithium quinolinol (Liq), which is relatively inexpensive and readily available, is particularly preferred.

[0151] The ionization potential of the electron transport layer is not particularly limited, but is preferably 5.6 eV to 8.0 eV, and more preferably 5.6 eV to 7.0 eV.

[0152] The method for forming each of the above layers constituting the organic EL element is not particularly limited and can include resistance heating deposition, electron beam deposition, sputtering, molecular stacking, and coating methods, but resistance heating deposition or electron beam deposition is generally preferred from the viewpoint of element characteristics.

[0153] (Electron injection layer) In the present invention, an electron injection layer may be placed between the cathode and the electron transport layer. Generally, the electron injection layer is placed to assist in the injection of electrons from the cathode to the electron transport layer. If placed, a layer containing a compound having a heteroaryl ring structure containing electron-accepting nitrogen may be used, or a layer containing the above-mentioned donor material may be used.

[0154] Furthermore, inorganic materials such as insulators and semiconductors can be used in the electron injection layer, and known materials can be used. By using these materials, short-circuit phenomena in organic EL devices can be suppressed and electron injection performance can be improved.

[0155] The compounds used as such insulators are preferably at least one metal compound selected from the group consisting of alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides, and alkaline earth metal halides.

[0156] Furthermore, complexes of organic compounds and metals are also suitably used. When an organic compound and metal complex is used in the electron injection layer, the film thickness can be easily adjusted. Preferred examples of organic compounds in organometallic complexes include quinolinol, benzoquinolinol, pyridylphenol, flavonol, hydroxyimidazopyridine, hydroxybenzazole, and hydroxytriazole.

[0157] Alkali metal atoms, alkaline earth metal atoms, or rare earth metal atoms are also suitably used as electron injection materials from the viewpoint of improving electron transport characteristics with a low work function. Among these, alkali metal atoms and rare earth metal atoms are more preferred from the viewpoint of further reducing the driving voltage of the organic EL.

[0158] Furthermore, layers containing the compound represented by general formula (1) are also preferred because they have high electron injection properties and exhibit excellent properties as electron injection layers. In addition, it is preferable that the electron injection layer contains the compound represented by general formula (1) and alkali metal atoms, rare earth metal atoms, or copper group atoms. In this case, the driving voltage can be further reduced and the durability life can be further improved.

[0159] (Charge Generation Layer) The charge generation layer in the present invention generally consists of a double layer, and more specifically, a pn junction charge generation layer consisting of an n-type charge generation layer and a p-type charge generation layer is preferably used. The above pn junction type charge generation layer generates charge or separates charge into holes and electrons when a voltage is applied in an organic EL element, and injects these holes and electrons into the light-emitting layer via a hole transport layer and an electron transport layer. A specific use of the charge generation layer is in an organic EL element in which multiple light-emitting layers are stacked separately, and it is used as a layer that is placed in the middle of the multiple light-emitting layers and is responsible for the function of charge generation. 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. As a result, the luminous efficiency of the organic EL element with multiple light-emitting layers stacked can be further improved, the driving voltage can be reduced, and the durability life of the element can be further improved.

[0160] The n-type charge generation layer consists of an n-type dopant material and a host material, and conventional materials can be used for these. For example, alkali metals, alkaline earth metals, or rare earth metals can be used as the n-type dopant material. As the host material, compounds having nitrogen-containing aromatic heterocycles, such as phenanthroline derivatives and oligopyridine derivatives, can be used. In particular, compounds represented by general formula (1) or phenanthroline dimers are preferred as host materials for the n-type charge generation layer because they exhibit excellent properties.

[0161] In one embodiment of the charge generation layer, it is preferable to further contain a phenanthroline derivative other than the compound represented by general formula (1). Examples of phenanthroline derivatives used in this case include the following compounds.

[0162]

[0163] In one embodiment of the charge generation layer, it is preferable to further contain an alkali metal atom, a copper group atom, or a rare earth metal atom in addition to the compound represented by general formula (1). Li is particularly preferred as the alkali metal atom. Ag is particularly preferred as the copper group atom. Yb is particularly preferred as the rare earth metal atom.

[0164] As one embodiment of the charge generation layer, a configuration that further includes a phenanthroline derivative and an alkali metal atom, a copper group atom, or a rare earth metal atom in addition to the compound represented by general formula (1) is also preferred.

[0165] The p-type charge generation layer consists of a p-type dopant and a host, and conventional materials can be used for these. For example, as p-type dopants, tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), tetracyanoquinodimethane derivatives, radialene derivatives, indacene derivatives, iodine, FeCl ３ FeF ３ SbCl ５ These can be used. Preferably, the p-type dopant is a radialene derivative or an indacene derivative. Preferably, the host is an arylamine derivative.

[0166] Preferred p-type dopants include the following compounds:

[0167]

[0168] 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 thicknesses of the light-emitting layer, electron transport layer, and hole transport layer are preferably 1 nm to 200 nm, and more preferably 5 nm to 100 nm.

[0169] The light-emitting element of the present invention has the function of converting electrical energy into light. While direct current is primarily used as the electrical energy, pulsed current and alternating current can also be used. There are no particular restrictions on the current and voltage values, but considering the power consumption and lifespan of the element, they should be selected to obtain maximum brightness with the lowest possible energy.

[0170] The light-emitting element of the present invention is suitably used, for example, as a display device such as a display that displays in a matrix and / or segment format. It is also suitably used as a display device such as a display having an optical sensor for which thinning and weight reduction are being considered.

[0171] The light-emitting element of the present invention is suitably used as a display device such as a display in various electronic devices. For example, since electronic devices such as mobile phones, smartphones, tablet terminals, laptop PCs, and wearable devices are being considered for power saving and extended lifespan, the light-emitting element of the present invention can provide electronic devices with higher durability than conventional ones.

[0172] The light-emitting element 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 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.

[0173] The light-emitting element of the present invention is also preferably used in various lighting devices. The light-emitting element of the present invention can achieve both high luminous efficiency and high color purity, and furthermore, it can be made thinner and lighter, thus enabling the realization of lighting devices that combine low power consumption, vivid light color, and high design quality.

[0174] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0175] Synthesis Example 1: Synthesis of Compound 1 19.5 g of starting material A, as described in the synthesis scheme below, was dissolved in 180 ml of tetrahydrofuran. To this solution, 39 ml of n-butyllithium (1.6 M hexane solution) was added dropwise under a nitrogen stream at 0°C, and the mixture was stirred at 0°C for 1 hour to obtain starting material solution A. Then, to a mixture of 14.5 g of 2-phenyl-1,10-phenanthroline and 180 ml of tetrahydrofuran at 0°C, starting material solution A at 0°C was added dropwise to obtain the reaction solution. After raising the reaction solution to room temperature, the precursor of intermediate A was extracted from the reaction solution with ethyl acetate, and the ethyl acetate containing the precursor was evaporated until 100 ml was obtained. 6.1 g of p-benzoquinone was added to the obtained solution, and the mixture was stirred at room temperature for 1 hour. Then, 60 ml of 1 mol / L aqueous sodium hydroxide solution was added, and the mixture was stirred overnight. The precipitated solid was filtered, washed with methanol, and vacuum dried to obtain 10.8 g of intermediate A (see synthesis scheme below).

[0176] Next, a mixed solution of 5.0 g of intermediate A, 5.0 g of boronic acid ester A, 160 mg of dichlorobis(triphenylphosphine palladium) dichloride, 10 ml of 1.5 M tripotassium phosphate aqueous solution, and 55 ml of 1,4-dioxane was heated and stirred under reflux under a nitrogen stream for 7 hours. After cooling to room temperature, water was added, the precipitated solid was filtered off, washed with methanol, and vacuum dried. The obtained solid was dissolved in pyridine solvent, and the catalyst was removed using activated carbon. The solvent was removed by evaporation, and the resulting solid was washed with toluene and methanol, then vacuum dried to obtain 5.8 g of compound 1 (see synthesis scheme below).

[0177] For the obtained compound 1, use an oil diffusion pump to perform 1 × 10 －３ Sublimation purification was performed at approximately 330°C under Pa pressure. The HPLC purity (area %) of compound 1 at a measurement wavelength of 254 nm) was 99.9% both before and after sublimation purification.

[0178] After sublimation purification, mass spectral (MS) analysis and １ The structure of compound 1 was identified by 1H-NMR analysis. The analysis results are shown below. MS (m / z): 716 [M + H] ＋ １ H-NMR (400MHz, CDCl３ ) δ: 8.88 (d, 2H), 8.67 (m, 1H), 8.42 (d, 2H), 8.35 (d, 1H), 8.29 (d, 1H), 8.16 (d, 1H), 8.13-8.07 (m , 4H), 7.99 (d, 1H), 7.88-7.76 (m, 4H), 7.73-7.67 (m, 2H), 7.62-7.58 (m, 1H), 7.57-7.35 (m, 12H).

[0179]

[0180] Synthesis Example 2: Synthesis of Compound 3 25 g of starting material B, as described in the synthesis scheme below, was dissolved in 180 ml of tetrahydrofuran. To this solution, 52 ml of n-butyllithium (1.6 M hexane solution) was added dropwise under a nitrogen stream at 0°C, and the mixture was stirred at 0°C for 1 hour to obtain starting material solution B. Then, to a mixture of 19 g of 2-phenyl-1,10-phenanthroline and 180 ml of tetrahydrofuran at 0°C, starting material solution B at 0°C was added dropwise to obtain the reaction solution. After raising the reaction solution to room temperature, the precursor of intermediate B was extracted from the reaction solution with ethyl acetate, and the ethyl acetate containing the precursor was evaporated until 100 ml was obtained. 7.9 g of p-benzoquinone was added to the obtained solution, and the mixture was stirred at room temperature for 1 hour. Then, 160 ml of 1 mol / L aqueous sodium hydroxide solution was added, and the mixture was stirred overnight. The precipitated solid was filtered, washed with methanol, and vacuum dried to obtain 16.8 g of intermediate B (see synthesis scheme below).

[0181] Next, a mixed solution of 3.0 g of intermediate B, 2.9 g of boronic acid ester A, 90 mg of dichlorobis(triphenylphosphine palladium) dichloride, 4 ml of 1.5 M tripotassium phosphate aqueous solution, and 28 ml of 1,4-dioxane was heated and stirred under reflux under a nitrogen stream for 7 hours. After cooling to room temperature, water was added, the precipitated solid was filtered off, washed with methanol, and vacuum dried. The obtained solid was dissolved in pyridine solvent, and the catalyst was removed using activated carbon. The solvent was removed by evaporation, and the resulting solid was washed with toluene and methanol, then vacuum dried to obtain 2.9 g of compound 3 (see synthesis scheme below).

[0182] The obtained compound 3 was subjected to 1 × 10⁻⁶ treatment using an oil diffusion pump. －３Sublimation purification was performed at approximately 330°C under Pa pressure. The HPLC purity (area %) of compound 3 before and after sublimation purification was 99.9% in both cases, at a measurement wavelength of 254 nm.

[0183] After sublimation purification, mass spectral (MS) analysis and １ The structure of compound 3 was identified by 1H-NMR analysis. The analysis results are shown below. MS (m / z): 690 [M + H] ＋ １ H-NMR (400MHz, CDCl ３ ) δ: 9.11-9.08 (m, 1H), 8.47-8.42 (m, 2H), 8.24-8.13 (m, 3H), 8.08-7.91 (m, 6H), 7.75-7.54 (m, 7H), 7.51-7.48 (m, 1H), 7.40-7.32 (m, 4H).

[0184]

[0185] Next, the evaluation methods for each embodiment will be described. Each evaluation was performed with n=1.

[0186] (Driving voltage) The elements obtained in Examples 1 to 24 and Comparative Examples 1 to 12 were each driven at 10 mA / cm². ２ The device was driven by DC current, and the initial drive voltage was measured. Furthermore, under conditions of 70°C, the current density was 10 mA / cm². ２ The voltage was measured after 100 hours of DC operation, and the voltage rise from the initial operating voltage was calculated.

[0187] Furthermore, the light-emitting elements obtained in Examples 25 to 82 and Comparative Examples 13 to 42 were each given a brightness of 1000 cd / m². ２ The device was lit and the initial drive voltage was measured. Furthermore, at room temperature, the current density was 10 mA / cm². ２ The voltage was measured after 100 hours of constant current operation, and the voltage rise from the initial drive voltage was calculated.

[0188] A lower initial drive voltage allows for operation at lower voltages, resulting in superior luminous efficiency (brightness / power). Furthermore, a smaller voltage rise indicates a longer lifespan.

[0189] (External quantum efficiency) The light-emitting devices obtained in Examples 25 to 82 and Comparative Examples 13 to 42 were measured at a current density of 10 mA / cm². ２ The device was lit, its external quantum efficiency was measured, and its luminous efficiency was evaluated. A higher external quantum efficiency indicates superior luminous efficiency.

[0190] (Durability) The light-emitting elements obtained in Examples 25-82 and Comparative Examples 13-42 were subjected to a voltage of 10 mA / cm². ２ The device was continuously driven with a constant current, and the time it took for the brightness to decrease by 20% from the initial brightness was measured to determine its durability.

[0191] [Example 1] A glass substrate (manufactured by Geomatec Co., Ltd., 11Ω / □, sputtered) with a 125 nm ITO transparent conductive film deposited as the anode was cut to 38 mm × 46 mm 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. This substrate was UV-ozone treated for 1 hour immediately before fabricating a single-charge element, and then placed in a vacuum deposition apparatus, where the vacuum level inside the apparatus was 5 × 10⁻⁶. －４ The system was evacuated until the pressure dropped below Pa. Compound 1 and the dopant material, metal element Yb, were deposited at a rate ratio of 1:1 such that 100 nm of deposition was used, forming a layer with a weight ratio of 9:1. Subsequently, 60 nm of aluminum was deposited to form the cathode, and a 5 mm x 5 mm single-charge element was fabricated. The film thickness mentioned here is the value displayed on a quartz crystal oscillating film thickness monitor and is common to other examples and comparative examples as well.

[0192] When this single-charge element was evaluated using the method described above, the initial drive voltage was 0.106V, and the voltage rise after 100 hours of operation at 70°C was 0.009V.

[0193] [Examples 2-24], [Comparative Examples 1-12] Single-charge elements were fabricated in the same manner as in Example 1, except that the compounds, metal elements, and the deposition rate ratio of the compounds to the metal elements were changed as shown in Table 1. The results for each example and comparative example are shown in Table 1. Compounds 1-12 are the compounds shown below.

[0194]

[0195]

[0196] [Example 25] A glass substrate with a reflective electrode (Geomatec Co., Ltd., 11Ω / □, sputtered) on which a 165 nm transparent ITO conductive film was deposited as the anode was cut to 38 mm × 46 mm and etched. The resulting substrate was ultrasonically cleaned for 15 minutes using "Semicoclean" 56 (product name, manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water. This substrate was UV-ozone treated for 1 hour immediately before fabricating the light-emitting element, and then placed in a vacuum deposition apparatus, where the vacuum level inside the apparatus was 5 × 10⁻⁶. －４ The atmosphere was evacuated until the pressure dropped below Pa. Using the resistance heating method, first, P-D1 was deposited at a thickness of 5 nm as a hole injection layer, and then HT-1 was deposited at a thickness of 50 nm as a hole transport layer. Next, a mixed layer of host material H-1 and dopant material D-1 was deposited at a thickness of 20 nm with a dope concentration of 5 wt% as an emissive layer. Next, ET-1 and 2E-1 were deposited at a thickness of 35 nm as an electron transport layer with a deposition rate ratio of ET-1 to 2E-1 = 1:1. Next, compound 1 and the dopant material metal element Yb were deposited at a thickness of 10 nm as an electron injection layer with a deposition rate ratio of compound 1:Yb = 9:1. After that, aluminum was deposited at a thickness of 60 nm to form the cathode, and a 5 mm × 5 mm square light-emitting device was fabricated.

[0197] When this light-emitting element was evaluated using the method described above, the initial drive voltage was 4.52V, the external quantum efficiency (luminescent efficiency) was 5.25%, the lifespan was 1100 hours, and the voltage rise after 100 hours of operation at room temperature was 0.054V. P-D1, HT-1, H-1, D-1, ET-1, and 2E-1 are the compounds shown below.

[0198]

[0199] [Examples 26-46] [Comparative Examples 13-24] Light-emitting devices were fabricated in the same manner as in Example 25, except that the compounds, metal elements, and the deposition rate ratio of the compounds to the metal elements were changed as shown in Table 2. The results for each example and comparative example are shown in Table 2.

[0200]

[0201] [Example 47] A glass substrate with a reflective electrode (manufactured by Intree) was cut to 38 mm x 46 mm to be used as the anode, and etched. The resulting substrate was ultrasonically cleaned for 15 minutes using "Semicoclean" 56 (trade name, manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water. This substrate was UV-ozone treated for 1 hour immediately before fabricating the light-emitting element, and then 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, P-D1 was deposited at a thickness of 5 nm as a hole injection layer, and then HT-1 was deposited at a thickness of 50 nm as a hole transport layer. Next, a mixed layer of host material H-1 and dopant material D-1 was deposited at a thickness of 20 nm as an emissive layer, with a dope concentration of 5% by weight. Next, compound 1 and the dopant material, the metal element Li, were deposited at a thickness of 35 nm as an electron transport layer, with a deposition rate ratio of compound 1:Li = 99:1. Next, Li was deposited at a thickness of 1 nm as an electron injection layer. After that, IZO was deposited as a cathode using a 100 nm sputtering method, and a 5 mm × 5 mm square light-emitting device was fabricated.

[0202] When this light-emitting element was evaluated using the method described above, the initial drive voltage was 3.97V, the external quantum efficiency (luminescent efficiency) was 6.49%, and the endurance life was 1270 hours.

[0203] [Examples 48-58] [Comparative Examples 25-30] Light-emitting devices were fabricated in the same manner as in Example 47, except that the compounds used were changed as shown in Table 3. The results for each example and comparative example are shown in Table 3.

[0204]

[0205] [Example 59] A glass substrate (manufactured by Geomatec Co., Ltd., 11Ω / □, sputtered) on which a 165 nm transparent ITO conductive film was deposited as the anode was cut to 38 mm × 46 mm and etched. The resulting substrate was ultrasonically cleaned for 15 minutes using "Semicoclean" 56 (product name, manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water. This substrate was UV-ozone treated for 1 hour immediately before fabricating the light-emitting element, and then placed in a vacuum deposition apparatus, where the vacuum level inside the apparatus was 5 × 10⁻⁶.－４ The system was evacuated until the pressure dropped below Pa. First, a 5 nm layer of P-D1 was deposited as a hole injection layer using the resistance heating method. Next, a light-emitting unit (first light-emitting unit) consisting of a hole transport layer, a light-emitting layer, and an electron transport layer was formed on the hole injection layer.

[0206] Specifically, HT-1 was deposited to a thickness of 50 nm as a hole transport layer, then a mixed layer of host material H-1 and dopant material D-1 was deposited to a thickness of 20 nm as an emissive layer with a doping concentration of 5% by weight, and then ET-1 and 2E-1 were deposited to a thickness of 35 nm as an electron transport layer with a deposition rate ratio of ET-1 to 2E-1 = 1:1.

[0207] On the first light-emitting unit, compound 1 and the dopant material metal element Yb were deposited at a rate ratio of compound 1:Yb = 9:1 to a thickness of 10 nm as an N-type charge generation layer, and then P-D1 was deposited at a thickness of 10 nm as a P-type charge generation layer.

[0208] Following the charge generation layer, a second light-emitting unit was formed in the same manner as the first light-emitting unit. Subsequently, compound 1 and the dopant material, the metal element Yb, were deposited at a deposition rate ratio of compound 1:Yb = 9:1 for 10 nm to form an electron injection layer, followed by a 60 nm deposition of aluminum to form the cathode, thereby fabricating a 5 mm x 5 mm square light-emitting device.

[0209] When this light-emitting element was evaluated using the method described above, the initial drive voltage was 8.81V, the external quantum efficiency (luminescent efficiency) was 10.25%, the lifespan was 1950 hours, and the voltage rise after 100 hours of operation at room temperature was 0.064V.

[0210] [Examples 60-82] [Comparative Examples 31-42] Light-emitting devices were fabricated in the same manner as in Example 59, except that the compounds used and the deposition rate ratio of the compounds to the metal elements were changed as shown in Table 4. The results for each example and comparative example are shown in Table 4.

[0211]

Claims

1. A compound represented by the following general formula (1). (In general formula (1), L is a substituted or unsubstituted arylene group or a substituted or unsubstituted heteroarylene group. However, if these groups are substituted, the substituents are alkyl or alkoxy groups. n is an integer from 2 to 5. Also, at least one of the n Ls is a structure represented by general formula (2). A is a substituted or unsubstituted pyrimidyl group, a substituted or unsubstituted triazinyl group, a substituted or unsubstituted quinoxalinyl group, or a substituted or unsubstituted quinazolinyl group. However, if these groups have substituents, the substituents do not form a ring structure. B is a hydrogen atom, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.) (In general formula (2), R １ ~R ４ Each of these is independently a hydrogen atom, an alkyl group, or an alkoxy group, and R １ ~R ４ These atoms do not bond to each other to form a ring. (* indicates the bond position with an adjacent substituent.) 2. The compound according to claim 1, wherein in the general formula (1), B is a substituted or unsubstituted aryl group.

3. The compound according to claim 1, wherein in the general formula (1), L is a substituted or unsubstituted arylene group.

4. In the general formula (2) above, R １ ~R ４ The compound according to claim 1, wherein is a hydrogen atom.

5. The compound according to claim 1, wherein n is 2 or 3 in the general formula (1).

6. A light-emitting element that emits light by electrical energy, wherein at least an electron transport layer and a light-emitting layer are present between an anode and a cathode, and the electron transport layer contains a compound according to any one of claims 1 to 5.

7. The light-emitting element according to claim 6, wherein the electron transport layer further contains alkali metal atoms, rare earth metal atoms, or alkali metal complex compounds.

8. The light-emitting element according to claim 7, wherein the electron transport layer contains an alkali metal atom, and the alkali metal atom is Li.

9. A light-emitting element that emits light by electrical energy, wherein at least a charge generating layer and a light-emitting layer are present between an anode and a cathode, and the charge generating layer contains the compound described in any one of claims 1 to 5.

10. The light-emitting element according to claim 9, wherein the charge generation layer further contains a phenanthroline derivative other than that of general formula (1).

11. The light-emitting element according to claim 9, wherein the charge-generating layer further contains alkali metal atoms or rare earth metal atoms.

12. The light-emitting element according to claim 11, wherein the charge-generating layer contains alkali metal atoms, and the alkali metal atoms are Li.

13. The light-emitting element according to claim 11, wherein the charge-generating layer contains a rare earth metal atom, and the rare earth metal atom is Yb.

14. A light-emitting element that emits light by electrical energy, wherein at least an electron injection layer and a light-emitting layer are present between an anode and a cathode, and the electron injection layer contains the compound described in any one of claims 1 to 5.

15. A display device comprising a light-emitting element containing the compound described in any one of claims 1 to 5.

16. An electronic device comprising a light-emitting element containing a compound according to any one of claims 1 to 5.

17. A lighting device comprising a light-emitting element containing the compound described in any one of claims 1 to 5.

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