JP5252482B2 - Light emitting element - Google Patents

Description

  The present invention relates to a light-emitting element having an organic thin film that can be used in the fields of display elements, flat panel displays, backlights, lighting, interiors, signs, signboards, electrophotographic machines, optical signal generators, and the like.

  A light-emitting element using an organic thin film has attracted attention and can be used for applications such as a solid, self-luminous large-area color display and illumination. The structure has a structure having two layers of a light emitting layer and a charge transport layer between a counter electrode composed of a cathode and an anode; an electron transport layer, a light emitting layer and a hole transport layer stacked between the counter electrodes. Known are those having a structure having three layers; and those having three or more layers; and those having a single light-emitting layer. Here, the hole transport layer has a function of injecting holes from the anode, transporting holes to the light emitting layer, facilitating injection of holes into the light emitting layer, and a function of blocking electrons. The electron transport layer has a function of injecting electrons from the cathode, transporting electrons to the light emitting layer, facilitating injection of electrons into the light emitting layer, and blocking holes. Further, in the light emitting layer, excitons are generated by recombination of the injected electrons and holes, and the energy emitted in the process of radiative deactivation of the excitons is detected as light emission.

A typical configuration of an early organic light-emitting device is one in which a porphyrin-based hole transport material, a light-emitting material, and Ag as a cathode are sequentially provided on a transparent electrode (see Patent Document 1).
In addition, a multilayer structure in which a hole injection layer, an electron injection layer, an electron block layer, a hole block layer, and the like are stacked, a phosphorescent organic EL element using a triplet light emitting material, and the like have been presented (Non-Patent Document 1 and 2).

  Recently, products having organic light-emitting elements have been sold in full-color displays and television monitors of mobile phones, and the performance has been improved to a level where there is no practical problem. However, if the organic light-emitting device is still stored under high temperature conditions or driven for a long time, stability problems such as changes in emission color, increase in drive voltage, decrease in light emission efficiency, and shortening of the device life may occur. Remaining. Further improvement of light emission efficiency and reduction of power consumption due to high driving voltage are also issues to be improved.

  In order to prevent the deterioration of the element, it is effective to increase the TG point (glass transition temperature) of the constituent material mainly including the hole transport layer, and the transport layer is hardly crystallized. Numerous studies have been made to obtain a layer having a molecular structure. However, for example, as in Patent Document 2, a charge transport layer formed of a compound containing a large amount of aromatic groups in the structure has a high TG point, but the sublimation temperature of the compound necessary for forming the transport layer is high. However, when the device is produced, there are problems such that the compound itself is easily decomposed and the uniformity of the produced transport layer is insufficient. For this reason, further improvements such as extending the lifetime of the device and improving the light emission efficiency by pioneering the materials to be used are continued.

  On the other hand, as benzochalcogenobenzochalcogenophene derivatives, diphenylbenzothienobenzothiophene derivatives and diphenylbenzoselenobenzoselenophene derivatives are known as materials for organic transistors (see Patent Document 3, Non-Patent Documents 3 and 4). . However, no example of using these derivatives as materials for light-emitting elements has been reported.

Japanese Patent Publication No. 64-7635 Japanese Patent No. 3833742 WO2006 / 077788 Jpn. J. et al. of Appl. Phys. , 27, L269-271 (1988) Appl. Phys. Lett. , 77, 904 (2000) J. et al. Am. Chem. Soc. 2006, 128, 3044-3050 J. et al. Am. Chem. Soc. 2006, 128, 12604-12605

  An object of the present invention is to solve the above-described problems, and to provide a light-emitting element that has high luminous efficiency and is stable even when used for a long time, and a derivative of a heterocyclic polycyclic compound used for the light-emitting element.

    The present inventors have found that the above-mentioned problems can be solved by using a derivative of a specific heteropolycyclic compound as a material for a light-emitting element, and have completed the present invention.

（式中、Ｘ_１およびＸ_２はそれぞれ独立に酸素原子、硫黄原子、又はセレン原子を表す。Ａ_１〜Ａ_４は水素原子又は置換基を有してもよい芳香族残基を表す。Ａ_１とＡ_２、及び（又は）Ａ_３とＡ_４は、互いに結合してそれぞれ独立に窒素原子と共に環を形成してもよい。）
（２）上記式（１）においてＸ_１及びＸ_２が硫黄原子である、（１）に記載の発光素子。
（３）陽極と陰極の間にある前記有機薄膜が複数層で形成される、（１）又は（２）に記載の発光素子。
（４）前記有機薄膜を形成する複数層が積層構造を有する、（１）から（３）のいずれか一つに記載の発光素子。
（５）前記有機薄膜を形成する複数層の少なくとも一層が正孔輸送層である、（１）から（４）のいずれか一つに記載の発光素子。
（６）上記式（１）に示す化合物を正孔輸送材料として正孔輸送層に含有する、（１）から（５）のいずれか一つに記載の発光素子。
（７）下記式（２）で示される化合物。

（式中、Ａ_１〜Ａ_４は水素原子又は置換基を有してもよい芳香族残基を表す。Ａ_１とＡ_２、及び（又は）Ａ_３とＡ_４は、互いに結合してそれぞれ独立に窒素原子と共に環を形成してもよい。） That is, the present invention has the following configuration.
(1) A light emitting device having an organic thin film formed of one layer or a plurality of layers between an anode and a cathode, wherein at least one layer of the organic thin film contains a compound represented by the following formula (1).

(In the formula, X ₁ and X ₂ each independently represent an oxygen atom, a sulfur atom, or a selenium atom. A _{1 to} A ₄ represent a hydrogen atom or an aromatic residue that may have a substituent. ₁ and A ₂ and / or A ₃ and A ₄ may be bonded to each other to form a ring together with a nitrogen atom.)
(2) The light emitting device according to (1), wherein X ₁ and X ₂ in the formula (1) are sulfur atoms.
(3) The light emitting device according to (1) or (2), wherein the organic thin film between the anode and the cathode is formed of a plurality of layers.
(4) The light emitting device according to any one of (1) to (3), wherein the plurality of layers forming the organic thin film have a laminated structure.
(5) The light emitting device according to any one of (1) to (4), wherein at least one of the plurality of layers forming the organic thin film is a hole transport layer.
(6) The light emitting device according to any one of (1) to (5), wherein the compound represented by the formula (1) is contained in a hole transport layer as a hole transport material.
(7) A compound represented by the following formula (2).

_(Wherein, A 1 to A ₄ is .A ₁ and _{A 2,} and (or) _{A 3} and _{A 4} represents an aromatic residue which may have a hydrogen atom or a substituent, combined with each other A ring may be formed independently with a nitrogen atom.)

  In the light-emitting device containing the heteropolycyclic compound of the present invention, the charge transport layer is hardly crystallized, and the device can be easily manufactured. Even at a low voltage, the luminance of light emission is high, the light emission efficiency is high, and the stability is also good. Therefore, it can be suitably used for a wide range of applications such as backlights for flat panel displays, illumination, display boards, marker lamps, liquid crystal displays, and the like.

Preferred embodiments of the light emitting device of the present invention are described below.
The light-emitting element of the present invention is an element that emits light by electric energy, in which one or more organic thin films are formed between an anode and a cathode, and is generally called an organic EL device or the like.

  The anode that can be used in the present invention is an electrode having a function of injecting holes into a hole injection layer, a hole transport layer, and a light emitting layer. In general, metal oxides, metals, alloys, conductive materials, and the like having a work function of 4.5 eV or more are suitable. Specifically, although not particularly limited, conductive metal oxides such as tin oxide (NESA), indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), gold, silver, platinum, chromium, Examples thereof include metals such as aluminum, iron, cobalt, nickel, and tungsten, inorganic conductive materials such as copper iodide and copper sulfide, conductive polymers such as polythiophene, polypyrrole, and polyaniline, and carbon. Among these, it is preferable to use ITO or NESA.

  If necessary, the anode may be made of a plurality of materials or may be composed of two or more layers. The resistance of the anode is not limited as long as it can supply a current sufficient for light emission of the element, but it is preferably low resistance from the viewpoint of power consumption of the element. For example, an ITO substrate having a sheet resistance value of 300Ω / □ or less functions as an element electrode, but since it is possible to supply a substrate of several Ω / □, it is desirable to use a low-resistance product. The thickness of ITO can be arbitrarily selected according to the resistance value, but is usually 5 to 500 nm, preferably 10 to 300 nm. Examples of film forming methods such as ITO include a vapor deposition method, an electron beam method, a sputtering method, a chemical reaction method, and a coating method.

  The cathode that can be used in the present invention is an electrode having a function of injecting electrons into an electron injection layer, an electron transport layer, and a light emitting layer. In general, a metal or an alloy having a small work function (approximately 4 eV or less) is suitable. Specific examples include platinum, gold, silver, copper, iron, tin, zinc, aluminum, indium, chromium, lithium, sodium, potassium, calcium, and magnesium, although not particularly limited. Lithium, sodium, potassium, calcium, and magnesium are preferable for increasing the electron injection efficiency and improving the device characteristics. As the alloy, an alloy with a metal such as aluminum or silver containing these low work function metals or an electrode having a structure in which these are laminated can be used. An inorganic salt such as lithium fluoride can be used for the electrode having a laminated structure. Moreover, when light emission is taken out not to the anode side but to the cathode side, a transparent electrode that can be formed at a low temperature may be used. Examples of the film forming method include a vapor deposition method, an electron beam method, a sputtering method, a chemical reaction method, and a coating method, but are not particularly limited. The resistance of the cathode is not limited as long as it can supply a current sufficient for light emission of the device, but it is preferably low resistance from the viewpoint of power consumption of the device, and is preferably about several hundreds to several Ω / □. The film thickness is usually 5 to 500 nm, preferably 10 to 300 nm.

  Furthermore, for sealing and protection, oxides such as titanium oxide, silicon nitride, silicon oxide, silicon nitride oxide, germanium oxide, nitrides, or mixtures thereof, polyvinyl alcohol, vinyl chloride, hydrocarbon polymers, fluorine The cathode can be protected with a polymer, etc., and sealed with a dehydrating agent such as barium oxide, phosphorus pentoxide, or calcium oxide.

In order to extract light emission, it is generally preferable to form an electrode on a substrate that is sufficiently transparent in the light emission wavelength region of the element. Examples of the transparent substrate include a glass substrate and a polymer substrate. As the glass substrate, soda lime glass, non-alkali glass, quartz, or the like is used. The glass substrate may have a thickness sufficient to maintain mechanical and thermal strength, and a thickness of 0.5 mm or more is preferable. As for the material of the glass, it is better that there are few ions eluted from the glass, and alkali-free glass is preferred. As such, since soda lime glass provided with a barrier coat such as SiO ₂ is commercially available, it can also be used. Examples of the substrate made of a polymer other than glass include polycarbonate, polypropylene, polyethersulfone, polyethylene terephthalate, and an acrylic substrate.

  The organic thin film included in the light emitting device of the present invention is formed of one layer or a plurality of layers between the anode and cathode electrodes. By incorporating the compound represented by the above formula (1) into the organic thin film, an element that emits light by electric energy can be obtained.

The “layer” of one or more layers forming the organic thin film in the present invention is a hole transport layer, an electron transport layer, a hole transport light-emitting layer, an electron transport light-emitting layer, a hole block layer, an electron block As shown in the layer, the hole injection layer, the electron injection layer, the light emitting layer, or the following structural example 9), it means a single layer having the functions of these layers.
Examples of the configuration of the layer forming the organic thin film in the present invention include the following configuration examples 1) to 9), and any configuration may be used.

Configuration Example 1) Hole transport layer / electron transport light emitting layer.
2) Hole transport layer / light emitting layer / electron transport layer.
3) Hole transporting light emitting layer / electron transporting layer.
4) Hole transport layer / light emitting layer / hole blocking layer.
5) Hole transport layer / light emitting layer / hole blocking layer / electron transport layer.
6) Hole transporting light emitting layer / hole blocking layer / electron transporting layer.
7) In each of the combinations 1) to 6), a hole injection layer is further provided in front of the hole transport layer or the hole transport light emitting layer.
8) A structure in which an electron injecting layer is further provided before the electron transporting layer or the electron transporting light emitting layer in each of the combinations 1) to 7).
9) A configuration in which materials used in the combinations 1) to 8) are mixed, and only one layer containing the mixed materials is included.

In the above 9), a single layer formed of a material generally called a bipolar luminescent material; or only one layer including a luminescent material and a hole transport material or an electron transport material may be provided.
In general, with a multilayer structure, charges, that is, holes and / or electrons can be efficiently transported and these charges can be recombined. In addition, by suppressing the quenching of charges, the stability of the element can be prevented from being lowered and the light emission efficiency can be improved.

  The hole injection layer and the transport layer are formed by laminating a hole transport material alone or a mixture of two or more kinds of the materials. As the hole transport material, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1,1′-diamine, N, N′-dinaphthyl-N, Triphenylamines such as N′-diphenyl-4,4′-diphenyl-1,1′-diamine, bis (N-allylcarbazole) or bis (N-alkylcarbazole) s, pyrazoline derivatives, stilbene compounds, hydrazones In the case of a polymer compound, a triazole derivative, a heterocyclic compound typified by an oxadiazole derivative or a porphyrin derivative, or a polymer system, a polycarbonate, a styrene derivative, polyvinyl carbazole, polysilane, or the like having the monomer in the side chain can be preferably used. There is no particular limitation as long as a thin film necessary for device fabrication is formed, holes can be injected from the electrodes, and holes can be transported. The hole injection layer provided between the hole transport layer and the anode for improving the hole injection property includes phthalocyanine derivatives, starburst amines such as m-MTDATA, polythiophene such as PEDOT in the polymer system, polyvinyl Those prepared with carbazole derivatives and the like can be mentioned.

  As an electron transport material in the present invention, it is necessary to efficiently transport electrons from the negative electrode between electrodes to which an electric field is applied. The electron transport material has high electron injection efficiency, and it is preferable to transport the injected electrons efficiently. For this purpose, it is required that the material has a high electron affinity, a high electron mobility, excellent stability, and a substance that does not easily generate trapping impurities during manufacturing and use. As substances satisfying such conditions, quinolinol derivative metal complexes represented by tris (8-quinolinolato) aluminum complexes, tropolone metal complexes, perylene derivatives, perinone derivatives, naphthalimide derivatives, naphthalic acid derivatives, oxazole derivatives, oxadiazoles Derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, bisstyryl derivatives, pyrazine derivatives, phenanthroline derivatives, benzoxazole derivatives, quinoxaline derivatives, and the like are exemplified, but are not particularly limited. These electron transport materials are used alone, but may be laminated or mixed with different electron transport materials. Examples of the electron injection layer provided between the electron transport layer and the cathode for improving the electron injection property include metals such as cesium, lithium, and strontium, lithium fluoride, and the like.

  The hole blocking layer is formed by laminating and mixing hole blocking substances alone or two or more kinds. As the hole blocking substance, phenanthroline derivatives such as bathophenandroline and bathocuproin, silole derivatives, quinolinol derivative metal complexes, oxadiazole derivatives and oxazole derivatives are preferable. The hole blocking substance is not particularly limited as long as it is a compound that can prevent holes from flowing out from the cathode side to the outside of the device and thereby reducing luminous efficiency.

  The light emitting layer means an organic thin film that emits light, and can be said to be, for example, a hole transporting layer, an electron transporting layer, or a bipolar transporting layer having strong light emitting properties. The light emitting layer only needs to be formed of a light emitting material (host material, dopant material, etc.), which may be a mixture of a host material and a dopant material or a host material alone. Each of the host material and the dopant material may be one kind or a combination of a plurality of materials. The dopant material may be included in the host material as a whole, or may be included partially. The dopant material may be either laminated or dispersed. Examples of the light emitting layer include the above-described hole transport layer and electron transport layer. Materials used for the light-emitting layer include carbazole derivatives, anthracene derivatives, naphthalene derivatives, phenanthrene derivatives, phenylbutadiene derivatives, styryl derivatives, pyrene derivatives, perylene derivatives, quinoline derivatives, tetracene derivatives, perylene derivatives, quinacridone derivatives, coumarin derivative porphyrins. Derivatives and phosphorescent metal complexes (Ir complex, Pt complex, Eu complex, etc.) can be mentioned.

  Generally, these organic thin films are formed by resistance heating vapor deposition, electron beam vapor deposition, sputtering, molecular lamination method, coating method by dissolving or dispersing in solvent or resin (spin coating, casting, dip coating, etc.), Langmuir・ Blodget method and ink jet method are listed. Although not particularly limited, usually, resistance heating vapor deposition and electron beam vapor deposition are preferable in terms of characteristics. The thickness of each layer depends on the resistance value of the luminescent material and cannot be limited, but is selected from 0.5 to 5000 nm. Preferably it is 1-1000 nm, More preferably, it is 5-500 nm.

  Among the organic thin films in the present invention, light is emitted by electric energy by containing one or a plurality of thin films such as a light emitting layer, a hole transport layer, and an electron transport layer in the compound represented by the above formula (1). An element is obtained.

In the above formula (1) in the present invention, X ₁ and X ₂ each independently represent an oxygen atom, a sulfur atom, or a selenium atom. A _{1 to} A ₄ represent a hydrogen atom or an aromatic residue that may have a substituent. A ₁ and A ₂ and / or A ₃ and A ₄ may be bonded to each other to form a ring with a nitrogen atom independently.
In the above formula (2) in the present invention, A _{1 to} A ₄ represent a hydrogen atom or an aromatic residue which may have a substituent. A ₁ and A ₂ and / or A ₃ and A ₄ may be bonded to each other to form a ring with a nitrogen atom independently.
In the above formulas (1) and (2), A ₁ and A ₃ , and A ₂ and A ₄ may be the same, and all of A ₁ , A ₂ , A ₃ and A ₄ may be the same. it can.

Examples of the aromatic residue that may have a substituent of A _{1 to} A ₄ include aromatic hydrocarbon residues such as benzene, naphthalene, anthracene, phenanthrene, pyrene, benzopyrene, pyridine, pyrazine, pyrimidine, quinoline, Examples thereof include aromatic heterocyclic residues such as isoquinoline, pyrrole, indole, imidazole, carbazole, thiophene, furan, benzothiophene, and benzofuran, and benzoquinone, anthraquinone, pyran, and pyridone having substituents thereon. Preferably, residues such as benzene, naphthalene, pyridine and thiophene are used. A benzene residue and a naphthalene residue are particularly preferable.

  The substituent for the aromatic residue is not particularly limited, but may be an aliphatic hydrocarbon residue that may have a substituent, an aromatic residue that may have a substituent, a cyano group, an isocyano group, a thiocyanate. Group, isothiocyanato group, nitro group, acyl group, halogen atom, hydroxyl group, substituted or unsubstituted amino group, alkoxyl group, alkoxyalkyl group, optionally substituted aromatic oxy group, carboxyl group, carbamoyl group, Examples include aldehyde groups and alkoxycarbonyl groups. Among them, an aliphatic hydrocarbon residue which may have a substituent, an aromatic residue which may have a substituent, a cyano group, a nitro group, an acyl group, a halogen atom, a hydroxyl group, substituted or unsubstituted An amino group, an alkoxyl group, and an aromatic oxy group which may have a substituent are preferable. More preferred are an aliphatic hydrocarbon residue which may have a substituent, an aromatic residue which may have a substituent, a nitro group, a halogen atom, a substituted or unsubstituted amino group, and an alkoxyl group. Most preferably, it is the aliphatic hydrocarbon residue which may have a substituent, or the aromatic residue which may have a substituent.

  Examples of the aliphatic hydrocarbon residue which may have a substituent include a saturated or unsaturated linear, branched or cyclic aliphatic hydrocarbon residue which may have a substituent, and the number of carbon atoms is 1 to 20 are preferred. Saturated or unsaturated linear or branched aliphatic hydrocarbon residues include methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl, allyl, t-butyl, n -A butenyl group is mentioned. Examples of the cyclic aliphatic hydrocarbon residue include a cycloalkyl group having 3 to 12 carbon atoms, such as a cyclohexyl group, a cyclopentyl group, an adamantyl group, and a norbornyl group. These aliphatic hydrocarbon residues may be further substituted with the above substituents (excluding alkyl groups). More preferably, it is a C1-C6 alkyl group which may have a substituent.

  Examples of aromatic residues that may have a substituent include aromatic hydrocarbon residues such as benzene, naphthalene, anthracene, phenanthrene, pyrene, and benzopyrene, and pyridine, pyrazine, pyrimidine, quinoline, isoquinoline, pyrrole, indole, and imidazole. And aromatic heterocyclic residues such as carbazole, thiophene and furan, and benzoquinone, anthraquinone, pyran and pyridone having substituents on them. Preferred examples include benzene, naphthalene, pyridine, and thiophene residues. A benzene residue and a naphthalene residue are particularly preferable.

Examples of the acyl group include an alkylcarbonyl group having 1 to 10 carbon atoms and an arylcarbonyl group. An alkylcarbonyl group having 1 to 4 carbon atoms is preferred, and specific examples include an acetyl group and a propionyl group. Examples of the halogen atom include atoms such as fluorine, chlorine, bromine and iodine. Examples of the substituted or unsubstituted amino group include an amino group, a mono- or dialkylamino group, and a mono- or diaromatic amino group. Specific examples include a mono- or dimethylamino group, a mono- or diethylamino group, a mono- or dipropylamino group, a mono- or diphenylamino group, or a benzylamino group. Examples of the alkoxyl group include an alkoxyl group having 1 to 10 carbon atoms.
Examples of the alkoxyalkyl group include an alkoxy group having 1 to 10 carbon atoms and an alkyl group having 1 to 10 carbon atoms.

Examples of the aromatic oxy group include aromatic hydrocarbon oxy groups such as phenoxy group and naphthyloxy group having 6 to 20 carbon atoms, and heterocyclic oxy groups such as pyridyloxy group, quinolyloxy group, and thiophenoxy.
Examples of the alkoxycarbonyl group include alkoxycarbonyl groups having 1 to 10 carbon atoms.

A ₁ and A ₂ and / or A ₃ and A ₄ in the above formula (1) may be bonded to each other to form a ring together with a nitrogen atom. By bonding, a carbazole ring, a phenoxazine ring, a phenothiazine ring, a phenazine ring, an acridine ring, a dithienopyrrole ring, a difuropyrrole ring, a dithienopyrazine ring, a dithienooxazine ring and the like which may have a substituent can be formed.

(In the above reaction formula, X ₁ and X ₂ each independently represent an oxygen atom, a sulfur atom, or a selenium atom. A _{1 to} A ₄ represent a hydrogen atom or an aromatic residue that may have a substituent. (Halo represents a halogen atom. In Formula (1), A ₁ and A ₂ , and / or A ₃ and A ₄ may be bonded to each other to independently form a ring with a nitrogen atom.)

  The compound of the above formula (1) is prepared by preparing a halogeno (iodine) derivative (3) according to the method described in Non-Patent Documents 1 and 2 and using an aromatic boronic acid or boronic ester derivative. It can be easily or manufactured using a coupling reaction. That is, the compound of the above formula (1) can be obtained by subjecting the iodine derivative (3) and a suitable aromatic boronic acid derivative to the Suzuki-Miyaura coupling reaction in the presence of a palladium catalyst.

  Suitable specific examples of the compound represented by the above formula (1) are listed in Table 1. Here, hydrogen atom is H, phenyl group is Ph, 3-methylphenyl group is mT, 4-methylphenyl group is pT, 1-naphthyl group is NP, 2-thienyl group is Th, 2-pyridyl group is Py, An oxygen atom is represented as O, a sulfur atom as S, and a selenium atom as Se.

  Other specific compound examples satisfying the definition of the above formula (1) are listed below.

  The light-emitting element of the present invention can be obtained by forming one or more layers of the compound represented by the above formula (1) between the anode and cathode electrodes. Although there is no restriction | limiting in particular in the site | part which uses the compound represented by the said Formula (1), It can use suitably as a host material combined with the utilization in a positive hole transport layer or a light emitting layer, a dopant, and a dopant.

  In the light emitting device of the present invention, the compound represented by the formula (1) can be suitably used as a hole transport layer or a light emitting layer. For example, it can be used in combination with the above-described electron transport material, hole transport material, light emitting material, or the like. Preferably, quinolinol derivative metal complex represented by tris (8-quinolinolato) aluminum complex, tropolone metal complex, perylene derivative, perinone derivative, naphthalimide derivative, naphthalic acid derivative, bisstyryl derivative, pyrazine derivative, phenanthroline derivative, benzoxazole derivative Quinoxaline derivatives, triphenylamines, bis (N-allylcarbazole) or bis (N-alkylcarbazole) s, pyrazoline derivatives, stilbene compounds, hydrazone compounds, heterocyclic compounds represented by oxadiazole derivatives, etc. Although it is mentioned, it is not particularly limited. These can be used alone, but can also be used by laminating or mixing different materials.

Specific examples of the dopant material when the compound represented by the above formula (1) is used as a host material in combination with a dopant material include perylene derivatives such as bis (diisopropylphenyl) perylenetetracarboxylic imide, perinone derivatives, 4- (Dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM) and its analogs, metal phthalocyanine derivatives such as magnesium phthalocyanine, aluminum chlorophthalocyanine, rhodamine compounds, deazaflavin derivatives, coumarin derivatives , oxazine compounds, squarylium compounds, violanthrone compound, Nile red, 5-cyano pyrromethene derivatives such as pyromellitic main Ten over BF ₄ complex, further acetylacetone and benzoyl acetone and Fe as phosphorescent material Eu complexes having nantroline and the like as ligands, porphyrins such as Ir complexes, Ru complexes, Pt complexes, Os complexes, ortho metal metal complexes and the like can be used, but are not particularly limited thereto. When two types of dopants are mixed, it is also possible to obtain light emission with improved color purity by efficiently transferring energy from the host dye using an assist dopant such as rubrene. In any case, in order to obtain high luminance characteristics, it is preferable to dope those having a high fluorescence quantum yield.

  If the amount of dopant material used is too large, a concentration quenching phenomenon will occur, so it is usually used at 30 mass% or less with respect to the host material. Preferably it is 20 mass% or less, More preferably, it is 10 mass% or less. As a method for doping the host material with the dopant material in the light emitting layer, it can be formed by a co-evaporation method with the host material. It is also possible to use it sandwiched between host materials. In this case, the host material may be laminated as one or more dopant layers.

  These dopant layers can form each layer alone, or may be used by mixing them. In addition, as a polymer binder, the dopant material may be polyvinyl chloride, polycarbonate, polystyrene, polystyrene sulfonic acid, poly (N-vinylcarbazole), poly (methyl) (meth) acrylate, polybutyl methacrylate, polyester, polysulfone, Solvent-soluble resins such as polyphenylene oxide, polybutadiene, hydrocarbon resin, ketone resin, phenoxy resin, polysulfone, polyamide, ethyl cellulose, vinyl acetate, ABS resin, polyurethane resin, phenol resin, xylene resin, petroleum resin, urea resin, melamine resin Further, it can be used by being dissolved or dispersed in a curable resin such as an unsaturated polyester resin, an alkyd resin, an epoxy resin, or a silicone resin.

  Organic thin film formation methods include resistance heating vapor deposition, electron beam vapor deposition, sputtering, molecular lamination methods, and methods of coating by dissolving and dispersing in solvents and resins (spin coating, casting, dip coating, etc.), LB methods, inkjet methods, etc. It is not particularly limited. Usually, resistance heating vapor deposition and electron beam vapor deposition are preferable in terms of characteristics. The thickness of each layer is set according to the resistance value of the luminescent material, and thus cannot be limited, but is selected from 0.5 to 5000 nm. Preferably it is 1-1000 nm, More preferably, it is 5-500 nm.

  When the compound of the above formula (1) of the present invention is used, a light-emitting element with high emission efficiency and a long lifetime can be obtained.

  The light emitting device of the present invention can be suitably used as a flat panel display. It can also be used as a flat backlight. In this case, either a light emitting colored light or a light emitting white light can be used. The backlight is mainly used for the purpose of improving the visibility of a display device that does not emit light, and is used for a liquid crystal display device, a clock, an audio device, an automobile panel, a display board, a sign, and the like. In particular, conventional backlights for liquid crystal display devices, especially personal computers for which thinning is an issue, are difficult to thin because they are made of fluorescent lamps and light guide plates. Since the used backlight is characterized by thinness and light weight, the above problems are solved. Similarly, it can be usefully used for illumination.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited by these examples. In the examples, unless otherwise specified, parts represent parts by mass, and% represents mass%.

Synthesis example 1
Synthesis of N- (4-bromophenyl) carbazole (Compound No. 100) In a 100 mL three-necked flask under nitrogen atmosphere, carbazole (3.0 g, 18 mmol), p-dibromobenzene (10 g, 43 mmol), anhydrous o-xylene (50 mL) And deaerated for 20 minutes. Diphenylphosphinoferrocene (800 mg, 8 mol%), sodium-t-butoxide (1.9 g, 20 mmol), Pd ₂ (dba) ₃ .CHCl ₃ (744 mg, 4 mol%) were added and the mixture was refluxed for 60 hours. After completion of the reaction, the reaction solution was cooled to room temperature, the reaction solution was filtered using Hyflo Supercell, and the solvent was distilled off under reduced pressure. The crude product was purified by column chromatography (silica gel, batch, hexane, R _f = 0.2) to obtain a white solid (Compound No. 100). (3.6g, 62%)

Synthesis example 2
Synthesis of N- (4-dihydroxyboro) carbazole (Compound No. 101) Magnesium (603 mg, 25 mmol) was added to a 100 mL three-necked flask under a nitrogen atmosphere, and the compound No. 1 obtained in Synthesis Example 1 was added. A portion of a THF (25 mL) solution containing 100 (4.0 g, 12 mmol) was added dropwise. After adding a small amount of iodine and heating the solution using a heat gun, the remaining compound no. 100 THF solution was added dropwise and refluxed for 2 hours. After completion of the reflux, the mixture was cooled to −70 ° C., trimethylboric acid (2.1 mL, 18 mmol) was slowly added, the temperature was raised to room temperature, and the mixture was stirred for 14 hours. 6N Hydrochloric acid (30 mL) was added, and the mixture was extracted with ethyl acetate (30 mL × 3), washed with water (50 mL × 3), dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The crude product was washed with hot toluene to obtain a white solid (Compound No. 101) (2.4 g, 68%).

窒素雰囲気下２０ｍＬ二口フラスコに２，７−ジヨウド［１］ベンゾチエノフェノ［３．２−ｂ］ベンゾチエノフェン（８５７ｍｇ、１．７ｍｍｏｌ）、化合物Ｎｏ．１０１（１．５ｇ、５．２ｍｍｏｌ）、ＤＭＦ（３９ｍＬ）、リン酸三カリウム・ｎ水和物（５．９ｇ、２８ｍｍｏｌ）を加え２０分間脱気を行った。Ｐｄ（ＰＰｈ_３）_４（２００ｍｇ、１０ｍｏｌ％）を加え遮光を行い４４時間還流した。反応終了後溶液を水（２００ｍＬ）に注ぎ析出した固体を濾取し水（５０ｍＬ）、アセトン（１００ｍＬ）で洗浄し減圧乾燥を行った。粗生成物をクロロホルムでソックスレー抽出を行うことにより黄色固体（化合物Ｎｏ．５２）を得た（１．２ｇ、９４％）。更に、昇華精製を実施して黄色の結晶を得た。（０．４ｇ、３２％）

Synthesis example 3

In a 20 mL two-necked flask under a nitrogen atmosphere, 2,7-diiodo [1] benzothienopheno [3.2-b] benzothienophene (857 mg, 1.7 mmol), Compound No. 101 (1.5 g, 5.2 mmol), DMF (39 mL), and tripotassium phosphate n-hydrate (5.9 g, 28 mmol) were added and deaerated for 20 minutes. Pd (PPh ₃ ) ₄ (200 mg, 10 mol%) was added and the mixture was shielded from light and refluxed for 44 hours. After completion of the reaction, the solution was poured into water (200 mL), and the precipitated solid was collected by filtration, washed with water (50 mL) and acetone (100 mL), and dried under reduced pressure. The crude product was subjected to Soxhlet extraction with chloroform to obtain a yellow solid (Compound No. 52) (1.2 g, 94%). Further, sublimation purification was performed to obtain yellow crystals. (0.4g, 32%)

Synthesis example 4
Hereinafter, Compound No. synthesized in the same manner as in Synthesis Example 3 was used. The characteristics of 5 and 40 are shown in Table 2.

Example 1
A glass substrate (manufactured by Tokyo Sanyo Vacuum Co., Ltd., 14Ω / □ or less) on which an ITO transparent conductive film was deposited to 150 nm was cut into 25 × 25 mm and etched. The obtained substrate was subjected to ultrasonic cleaning with a neutral detergent for 10 minutes, ion-exchanged water for 5 minutes x 2 times, acetone for 5 minutes x 2 times, followed by isopropyl alcohol for 5 minutes x 2 times. The substrate was subjected to sonic cleaning, UV-ozone cleaning was performed for 10 minutes immediately before the device fabrication, and the substrate was placed in a vacuum vapor deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 3.0 × 10 ⁻³ Pa or less. First, as a hole transport material by resistance heating vapor deposition method, No. 1 of Synthesis Example 4 was used. 5 was deposited to a thickness of 50 nm to form a hole transport layer. Next, tris (8-quinolinolato) aluminum (ALQ3) was vapor-deposited to a thickness of 50 nm as a light emitting layer / electron transport layer. Further, lithium fluoride was deposited to a thickness of 0.8 nm and aluminum was deposited to a thickness of 100 nm to form a cathode, whereby a 2 × 2 mm square light emitting device was manufactured. The structure of this light emitting element is shown in FIG.
This light-emitting element showed a maximum luminance of 26631 cd / m ² (8.5 V), a threshold voltage of 4.0 V at which the emission luminance was 100 cd / m or higher, and a maximum current efficiency of 1.759 cd / A (6.0 V).

Example 2
A substrate processed in the same manner as in Example 1 was spin-coated with 20 nm of PEDOT: PSS, and the substrate provided with the hole injection layer was placed in a vacuum evaporation apparatus, and a light-emitting element was similarly manufactured. The structure of this light emitting element is shown in FIG. This light-emitting element showed a maximum luminance of 14000 cd / m ² (9.5 V), a threshold voltage of 4.5 V at which the emission luminance became 100 cd / m or more, and a maximum current efficiency of 2.814 cd / A (5.5 V).

Example 3
Compound No. 4 of Synthesis Example 4 In place of compound No. 5 A light emitting device was produced in the same manner as in Example 1 except that 52 was used. This light-emitting element showed a maximum luminance of 13036 cd / m ² (8.0 V), a threshold voltage of 6.0 V, and a maximum current efficiency of 0.224 cd / A (7.0 V).

Example 4
Compound No. 4 of Synthesis Example 4 In place of compound No. 5 A light emitting device was produced in the same manner as in Example 2 except that 52 was used. This light-emitting element exhibited a maximum luminance of 11985 cd / m ² (8.5 V), a threshold voltage of 4.5 V, and a maximum current efficiency of 2.030 cd / A (6.5 V).

Example 5
The substrate (20Ω / □ or less) on which a ITO transparent conductive film is deposited on a glass substrate to a thickness of 110 nm is washed and placed in a vacuum evaporation apparatus, and the degree of vacuum in the apparatus becomes 3.0 × 10 ⁻⁴ Pa or less. Was exhausted. First, as a hole transport material by resistance heating vapor deposition method, No. 1 of Synthesis Example 4 was used. 5 was deposited to a thickness of 50 nm to form a hole transport layer. Next, tris (8-quinolinolato) aluminum (ALQ3) was vapor-deposited to a thickness of 50 nm as a light emitting layer / electron transport layer. Further, an alloy of magnesium: silver = 9: 1 was deposited to a thickness of 100 nm and silver was deposited to a thickness of 10 nm to form a cathode, whereby a light emitting device was manufactured. The structure of this light emitting element is the same as that of the light emitting element of Example 1 shown in FIG.
This light emitting element had a driving voltage of 6.3 V at a current density of 100 mA / cm ² .

Comparative Example 1
No. 5 in Example 5. Instead of the compound 5, light emission using a general N, N′-dinaphthyl-N, N′-diphenyl-4,4′-diphenyl-1,1′-diamine (α-NPD) as a hole transport material An element was produced. The structure of this light emitting element is the same as that of the light emitting element of Example 1 shown in FIG.
This light-emitting element had a driving voltage of 7.4 V at a current density of 100 mA / cm ² , and Example 5 was found to be driven at a lower voltage.

Example 6
The substrate (20Ω / □ or less) on which a ITO transparent conductive film is deposited on a glass substrate to a thickness of 110 nm is washed and placed in a vacuum evaporation apparatus, and the degree of vacuum in the apparatus becomes 3.0 × 10 ⁻⁴ Pa or less. Was exhausted. First, N, N′-dinaphthyl-N, N′-diphenyl-4,4′-diphenyl-1,1′-diamine (α-NPD) is formed to a thickness of 50 nm as a hole transport material by resistance heating vapor deposition. The hole transport layer was formed by vapor deposition. Next, as a host material for the light emitting layer, the compound No. 1 of Synthesis Example 4 was used. 5 and 2% Ir (btp) ₂ acac as a guest material were co-evaporated to a thickness of 30 nm, and BAlq ₂ as an electron transport layer was evaporated to a thickness of 30 nm. Further, an alloy of magnesium: silver = 9: 1 was deposited to a thickness of 100 nm and a thickness of 10 nm of silver to form a cathode, and a light emitting device was manufactured.
This light-emitting element had a driving voltage of 8.4 V at a current density of 100 mA / cm ² , an external quantum efficiency of 2.72, and was found to be useful as a red phosphorescent element.
The chemical formulas of α-NPD, Ir (bpt) ₂ acac and BAlq ₂ are shown below.

1 shows a structure of a light-emitting element in Example 1. 2 shows a structure of a light-emitting element in Example 2.

Claims (7)

A light-emitting element having an organic thin film formed of one or more layers between an anode and a cathode, wherein at least one layer of the organic thin film contains a compound represented by the following formula (1).

(In the formula, X ₁ and X ₂ each independently represent an oxygen atom, a sulfur atom, or a selenium atom. A _{1 to} A ₄ represent a hydrogen atom or an aromatic residue that may have a substituent. ₁ and A ₂ , and / or A ₃ and A ₄ may be bonded to each other to form a ring together with a nitrogen atom. The light emitting element of Claim 1 whose X < ₁ > and X < ₂ > are sulfur atoms in the said Formula (1).   The light emitting device according to claim 1 or 2, wherein the organic thin film between the anode and the cathode is formed of a plurality of layers.   The light emitting element as described in any one of Claim 1 to 3 in which the multiple layers which form the said organic thin film have a laminated structure.   The light emitting element according to any one of claims 1 to 4, wherein at least one of the plurality of layers forming the organic thin film is a hole transport layer.   The light emitting element as described in any one of Claim 1 to 5 which contains the compound shown to said Formula (1) in a positive hole transport layer as a positive hole transport material. A compound represented by the following formula (2).

_(Wherein, A 1 to A ₄ is .A ₁ and _{A 2,} and (or) _{A 3} and _{A 4} represents an aromatic residue which may have a hydrogen atom or a substituent, combined with each other A ring may be formed independently with a nitrogen atom.)

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