TW201341360A - Light-emitting element - Google Patents

Abstract

Provided is a light-emitting element simultaneously exhibiting high light-emitting efficiency and durability. The light-emitting element of the present invention is a light-emitting element comprising at least a hole transport layer and a light-emitting layer between an anode and a cathode, and emitting light by electric energy and is characterized in that the hole transport layer contains a compound having a specific carbazole skeleton and the light-emitting layer contains a compound having an aromatic heterocyclic group containing an electron-accepting nitrogen.

Description

Light-emitting element

The present invention relates to a light-emitting element capable of converting electrical energy into light. More particularly, the present invention relates to light-emitting elements that can be utilized in the fields of display elements, flat panel displays, backlights, illumination, interior decoration, signage, billboards, electronic cameras, and optical signal generators.

Researches on so-called organic thin-film light-emitting elements that emit light when the electrons injected from the cathode and the holes injected by the anode are recombined in the organic phosphor sandwiched between the two electrodes have been actively carried out in recent years. The light-emitting element is characterized by being thin and capable of emitting light with high luminance at a low driving voltage, and is capable of generating multi-color light emission by selection of a fluorescent material, and thus attracts attention.

Since the research by CWTang et al. of Kodak Co., Ltd., a large number of practical researches have been published on high-intensity light-emitting organic thin film devices, and organic thin film light-emitting elements have also been used in mobile phones as main displays, and have indeed progressed practically. Chemical. However, there are still many technical problems, and it is one of the important issues to consider the high efficiency and longevity of components.

The driving voltage of the element is largely transmitted to the carrier transport material such as a hole and a so-called carrier such as electrons to the light-emitting layer. Among them, as a material for transporting holes (hole transport material), there is a material of a carbazole skeleton. The material is known (for example, refer to Patent Documents 1 to 2). Further, since the material having the carbazole skeleton has a high triplet energy level, it is known as a host material of the light-emitting layer (for example, refer to Patent Documents 3 to 4).

[Previous Technical Literature] [Patent Document]

Patent Document 1 Japanese Patent Publication No. 8-3547

Patent Document 2 Korean Patent Application Publication No. 2010-0079458

Patent Document 3 Japanese Patent Laid-Open Publication No. 2003-133075

Patent Document 4 International Publication No. 2011/132683

However, it has been difficult to sufficiently reduce the driving voltage of the element by the prior art. Even if the driving voltage of the device is lowered, the luminous efficiency and durability of the device are insufficient. As such, no technology has been found which combines high luminous efficiency and endurance life.

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic thin film light-emitting device which solves such a technical problem and improves luminous efficiency and durability.

In order to achieve the above object, a light-emitting element of the present invention is a light-emitting element having at least a hole transport layer and a light-emitting layer between an anode and a cathode, and which emits light by electric energy, wherein the hole transport layer includes the following a compound represented by the formula (1), and the aforementioned luminescence The layer is a compound having an aromatic heterocyclic group containing an electron-accepting nitrogen, and is a compound represented by the following formula (4).

(In the formula (1), each of R ³ to R ¹⁸ may be the same or different and is derived from hydrogen, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, or an alkane. Thio group, aryl ether group, aryl sulfide group, aryl group, heteroaryl group, halogen, carbonyl group, carboxyl group, oxycarbonyl group, amine mercapto group, amine group, fluorenyl group, and -P(=O)R ¹⁹ R The group consisting of ²⁰ is selected. R ¹⁹ and R ²⁰ are aryl or heteroaryl groups. L is a single bond, an arylene group or a heteroarylene group, but the two carbazole skeletons are in the range of R ⁷ to R ¹⁰ in any position, and R ¹¹ ~ R L connected to any one position among ¹⁴ wherein, R ¹ ~ R ¹⁸ lines contain dibenzofuran skeleton, dibenzothiophene skeleton and a carbazole skeleton .R ¹ It is a group represented by the following general formula (2).

In the formula (2), each of R ²¹ to R ²⁵ may be the same or different and is hydrogen, or an aryl group having a substituent or having no substituent. However, at least two of R ²¹ to R ²⁵ are a substituent or an aryl group having no substituent, and are composed only of an aromatic hydrocarbon. R ² is a group represented by the following formula (3).

In the formula (3), R ²⁶ to R ³⁰ each may be the same or different and are hydrogen or a substituted or unsubstituted aryl group, and are composed only of an aromatic hydrocarbon.

In the formula (4), R ⁵¹ to R ⁵⁵ and R ⁵⁶ to R ⁵⁷ each may be the same or different and are hydrogen, alkyl, cycloalkyl, heterocyclic, alkenyl, cycloalkenyl, alkynyl, alkane. Oxyl, alkylthio, aryl ether, aryl sulfide, aryl, heteroaryl, halogen, carbonyl, carboxyl, oxycarbonyl, aminecaraki, amine, or fluorenyl. Y ¹ is -N(R ⁵⁸ )-, -C(R ⁵⁹ R ⁶⁰ )-, an oxygen atom, or a sulfur atom. R ⁵⁸ to R ⁶⁰ each may be the same or different and are an alkyl group, an aryl group or a heteroaryl group. The adjacent substituents in R ⁵⁸ to R ⁶⁰ may form a ring with each other. L ² ~ L ⁴ is a single bond or an arylene group. X ¹ to X ⁵ represent a carbon atom or a nitrogen atom, and in the case where X ¹ to X ⁵ are a nitrogen atom, R ⁵¹ to R ⁵⁵ of the substituent on the nitrogen atom are not present. However, the number of nitrogen atoms in X ¹ to X ⁵ is 1 to 3. L ¹ is a single bond or an arylene group. )

According to the present invention, it is possible to provide an organic electric field light-emitting element having high luminous efficiency and having a sufficient durability.

[Formation of the Invention]

The light-emitting element of the present invention is a light-emitting element having at least a hole transport layer and a light-emitting layer between the anode and the cathode and emitting light by electric energy, wherein the hole transport layer is represented by the following general formula (1) The compound, and the light-emitting layer contains a compound having an aromatic heterocyclic group containing an electron-accepting nitrogen, and is a compound represented by the following formula (4).

The compound represented by the formula (4) having an aromatic heterocyclic group containing an electron-accepting nitrogen, which has high electron injecting and transporting energy, can be provided by using it as a light-emitting layer. An organic thin film light-emitting element having luminous efficiency and low driving voltage. However, since the luminescent layer has a very high electron injecting and transporting energy, according to the type of the hole transporting layer used in combination, the recombination region in the luminescent layer is localized on the side of the hole transporting layer, because the triplet energy and electrons will The hole transport layer leaks, which causes a decrease in luminous efficiency of the element and deterioration in durability.

On the other hand, the inventors of the present invention found that by using the compound represented by the general formula (1) as the hole transport layer, high luminous efficiency and durability can be greatly improved. That is, the compound represented by the general formula (1) has high electron blocking property and has high triplet energy, even if the recombination region in the light-emitting layer is localized on the side of the hole transport layer, since the triplet state can be Energy and electrons are kept in the light-emitting layer, which enables high efficiency and long life.

In other words, a compound represented by the formula (1) is used as the hole transport layer, and a compound represented by the formula (4) having an aromatic heterocyclic group having electron-accepting nitrogen is used as the light-emitting layer. High light A better combination of efficiency and durability.

The compound represented by the formula (1) in the present invention is explained in detail below.

In the formula (1), each of R ³ to R ¹⁸ may be the same or different and is derived from hydrogen, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, or an alkylthio group. Base, aryl ether group, aryl sulfide group, aryl group, heteroaryl group, halogen, carbonyl group, carboxyl group, oxycarbonyl group, amine mercapto group, amine group, fluorenyl group, -P(=O)R ¹⁹ R ²⁰ The group formed is selected. R ¹⁹ and R ²⁰ are an aryl or heteroaryl group. L is a single bond, an arylene group or a heteroarylene group. However, the two carbazole skeletons are bonded to L at any of R ⁷ to R ¹⁰ and at any of R ¹¹ to R ¹⁴ . Among them, R ¹ to R ¹⁸ do not contain a dibenzofuran skeleton, a dibenzothiophene skeleton, and a carbazole skeleton.

R ¹ is a group represented by the following formula (2).

In the formula (2), each of R ²¹ to R ²⁵ may be the same or different and is hydrogen, or an aryl group having a substituent or having no substituent. However, at least two of R ²¹ to R ²⁵ are a substituent or an aryl group having no substituent, and are composed only of an aromatic hydrocarbon.

R ² is a group represented by the following formula (3).

In the formula (3), R ²⁶ to R ³⁰ each may be the same or different and are hydrogen or a substituted or unsubstituted aryl group, and are composed only of an aromatic hydrocarbon.

A compound having a carbazole skeleton represented by the formula (1), which contains two carbazole skeletons in the molecule, and R ¹ to R ¹⁸ contains no dibenzofuran skeleton, a dibenzothiophene skeleton, and a carbazole skeleton. . Thereby, it has high film stability and excellent heat resistance. Among them, since there are some doubts about thermal decomposition in the case of having three or more carbazole skeletons, it is preferably two.

Further, the compound having a carbazole skeleton represented by the formula (1), the substituent on N is composed only of an aromatic hydrocarbon, and is at least two aryl groups having a substituent or no substituent. Phenyl group, showing excellent properties in electron blocking properties. The phenyl group of the substituent on N, by having at least two aryl groups as a substituent, makes the glass transition temperature (Tg) of the compound having the carbazole skeleton represented by the general formula (1) high, allowing electrons The barrier is significantly improved. As a result, the charge balance in the light-emitting layer can be improved, and the performance of the light-emitting element such as luminous efficiency and lifetime can be improved. Further, in the case of the phenyl group of the substituent on N, the number of the aryl groups of the substituent is three or more, and it is difficult to synthesize it due to being crowded in a three-dimensional space. Therefore, the number of the aforementioned aryl groups is preferably two.

Further, by allowing a compound having a carbazole skeleton represented by the general formula (1) to be a compound represented by the general formula (8), high hole transportability is exhibited, and hole movement in the layer is caused. It is possible to increase the low driving voltage.

In the formula (8), R ¹ to R ³ and R ¹⁸ are the same as described above.

By linking the carbazole skeleton, it is possible to maintain the high triplet energy level of the carbazole skeleton itself, and to achieve high luminescence efficiency by suppressing easy deactivation. In particular, R ¹ to R ² in the general formulae (1) and (8) are different groups. In this case, since the molecules become an asymmetrical structure, the effect of suppressing the interaction between the carbazole skeletons becomes high, and it is preferable that a stable film can be formed and durability is improved.

Moreover, the general formula R (1) is ¹ ~ R ^30, and formula (8) R ¹ ~ R ^3, and R ¹⁸ does not contain an anthracene skeleton and a pyrene-based backbone. In other words, the compound having a carbazole skeleton represented by the general formula (1) and the general formula (8) preferably contains no anthracene skeleton or an anthracene skeleton in the molecule. Since the ruthenium skeleton and the ruthenium skeleton have low triplet energy levels, the compound having the carbazole skeleton of the present invention causes a decrease in the triplet energy level of the compound in the case of having an anthracene skeleton or an anthracene skeleton as a substituent. In the case where a compound having a carbazole skeleton represented by the general formula (1) and the general formula (8) is used as a hole transport layer, if the triplet energy level is low, one and a triplet luminescent dopant are contained. When the luminescent layer is in direct contact, triplet excitation energy leakage occurs, and the luminous efficiency is lowered. Further, when a compound having a carbazole skeleton represented by the general formula (1) or the general formula (8) is used as the light-emitting layer, the effect of blocking the excitation energy of the triplet light-emitting material cannot be sufficiently exhibited, and the light emission is caused. Reduced efficiency.

The hydrogen among these substituents may also be hydrazine.

In the compounds represented by the general formula (1) and the general formula (8), the alkyl group means, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, secondary butyl, and tertiary butyl. A saturated aliphatic hydrocarbon group having the same or different substituents. The substituent to be added in the case of being substituted is not particularly limited, and examples thereof include an alkyl group, an aryl group, and a heteroaryl group. These points are common to the following description. Further, the carbon number of the alkyl group is not particularly limited, but is usually 1 or more and 20 or less, and more preferably 1 or more and 8 or less, from the viewpoint of availability and cost.

In the compounds represented by the general formulae (1) to (4), the cycloalkyl group means, for example, a saturated alicyclic hydrocarbon group such as a cyclopropyl group, a cyclohexyl group, a decyl group or an adamantyl group, with or without a substituent. Yes. The carbon number of the alkyl moiety is not particularly limited, and is usually in the range of 3 or more and 20 or less.

In the compounds represented by the general formula (1) and the general formula (8), the heterocyclic group means, for example, a hydrocarbyl ring, a piperidine ring or a cyclic decylamine, which is equal to an aliphatic ring having an atom other than carbon in the ring. It may or may not have a substituent. The carbon number of the heterocyclic group is not particularly limited, but is usually in the range of 2 or more and 20 or less.

In the compound represented by the formula (1), the alkenyl group means, for example, an unsaturated aliphatic hydrocarbon group containing a double bond such as a vinyl group, an allyl group or a butadienyl group, and may or may not have a substituent. The carbon number of the alkenyl group is not particularly limited, and is usually in the range of 2 or more and 20 or less.

In the compounds represented by the formula (1) and the formula (8), the cycloalkenyl group means, for example, an unsaturated alicyclic ring containing a double bond such as a cyclopentenyl group, a cyclopentadienyl group or a cyclohexenyl group. Hydrocarbyl groups, with or without substituents. The carbon number of the cycloalkenyl group is not particularly limited, and is usually 2 or more and 20 or less. range.

In the compounds represented by the formula (1) and the formula (8), the alkynyl group means, for example, an unsaturated aliphatic hydrocarbon group containing a triple bond such as an ethynyl group, which may or may not have a substituent. The carbon number of the alkynyl group is not particularly limited, and is usually in the range of 2 or more and 20 or less.

In the compounds represented by the formula (1) and the formula (8), the alkoxy group represents, for example, a functional group of an aliphatic hydrocarbon group bonded through an ether bond such as a methoxy group, an ethoxy group or a propoxy group. This aliphatic hydrocarbon group may or may not have a substituent. The carbon number of the alkoxy group is not particularly limited, and is usually in the range of 1 or more and 20 or less.

In the compound represented by the general formula (1) and the general formula (8), the oxygen atom of the ether bond of the alkylthio alkoxy group is substituted by a sulfur atom. The alkylthio group may or may not have a substituent. The carbon number of the alkylthio group is not particularly limited, and is usually in the range of 1 or more and 20 or less.

In the compounds represented by the formula (1) and the formula (8), the aryl ether group means, for example, a functional group of an aromatic hydrocarbon group bonded through an ether bond such as a phenoxy group, and the aromatic hydrocarbon group may or may not be substituted. Base can be. The carbon number of the aryl ether group is not particularly limited, and is usually in the range of 6 or more and 40 or less.

In the compound represented by the formula (1) and the formula (8), the oxygen atom of the ether bond of the aryl sulfide group-based aryl ether group is substituted by a sulfur atom. The aromatic hydrocarbon group of the aryl ether group may or may not have a substituent. The carbon number of the aryl ether group is not particularly limited, and is usually in the range of 6 or more and 40 or less.

In the compounds represented by the general formula (1) and the general formula (8), the aryl group means, for example, a phenyl group, a naphthyl group, a biphenyl group, a fluorenyl group, a phenanthryl group, a stretched triphenyl group, a terphenyl group, or the like. Aromatic hydrocarbon group. Aryl with or without substitution Base can be. The carbon number of the aryl group is not particularly limited, and is usually in the range of 6 or more and 40 or less.

In the compounds represented by the general formula (1) and the general formula (8), the heteroaryl group means: a furyl group, a phenylthio group, a pyridyl group, a pyrimidinyl group, and a third group. Base, quinolinyl, pyridyl base, A cyclic aromatic group having an atom other than carbon in one or more of the rings, such as a pyridyl group, a benzofuranyl group, a benzophenylthio group or a fluorenyl group, may be unsubstituted or substituted. The carbon number of the heteroaryl group is not particularly limited, and is usually in the range of 2 or more and 30 or less.

In the compounds represented by the formula (1) and the formula (8), the halogen means fluorine, chlorine, bromine or iodine.

In the compound represented by the formula (1) and the formula (8), a carbonyl group, a carboxyl group, an oxycarbonyl group or an aminecarbamyl group may or may not have a substituent, and examples of the substituent include an alkyl group. A cycloalkyl group, an aryl group or the like, these substituents may be further substituted.

In the compound represented by the formula (1) and the formula (8), the amine group may or may not have a substituent, and examples of the substituent include an aryl group and a heteroaryl group, and these substituents may also be used. Further replaced.

In the compounds represented by the general formula (1) and the general formula (8), the fluorenyl group may, for example, be a functional group having a bond to a ruthenium atom such as a trimethylsulfonyl group, and may or may not have a substituent. The carbon number of the fluorenyl group is not particularly limited, and is usually in the range of 3 or more and 20 or less. The number of turns is usually in the range of 1 or more and 6 or less.

In the compound represented by the formula (1), L is a single bond, an arylene group or a heteroarylene group. However, the two carbazole skeletons are bonded to L at any of R ⁷ to R ¹⁰ and at any of R ¹¹ to R ¹⁴ . Examples of arylene groups such as phenylene, naphthyl, phenyl, fluorenyl, phenanthrene, triphenyl, fluorenyl, fluorene, etc., heteroarylene Examples are: furfuryl, phenylthio, pyridine, quinolinyl, isoquinolyl, pyridyl Basis, pyrimidinyl, extens Pyridyl, benzofuranyl, benzophenylthio, decyl, dibenzofuranyl, dibenzophenylthio, carbazolyl and the like. It may or may not have a substituent.

Wherein the two carbazole skeletons are at any one of R ⁷ to R ¹⁰ and any one of R ¹¹ to R ¹⁴ is bonded to L, for example, at the position of R ⁸ and L. In the case, R ⁸ in one side of the carbazole skeleton is a bonded carbon atom, and is directly bonded to L. In this case, R ^{8 of the} substituent is not present.

On the other hand, the light-emitting element of the present invention is characterized in that the light-emitting layer is a compound having an electron-accepting nitrogen-containing aromatic heterocyclic group, and includes a compound represented by the following formula (4). The light-emitting layer includes a compound represented by the following formula (4), which is a compound having an electron-accepting nitrogen-containing aromatic heterocyclic group, and exhibits high electron injecting and transporting property, thereby improving luminous efficiency. Further, it is preferable because a stable film can be formed and durability is improved.

Hereinafter, the compound having an electron-accepting nitrogen-containing aromatic heterocyclic group represented by the formula (4) in the present invention will be described in detail.

The electron-accepting nitrogen referred to herein means a nitrogen atom which forms a multiple bond between adjacent atoms. This multiple bond has electron accepting properties due to the high electronegativity of the nitrogen atom. Therefore, the aromatic heterocyclic ring containing electron-accepting nitrogen has high electron affinity. a compound of the present invention having electron accepting nitrogen exhibiting high electron injecting transportability, The luminous efficiency is improved by increasing the probability of recombination.

The aromatic heterocyclic group containing electron accepting nitrogen means pyridyl, quinolyl, isoquinolinyl, quin Polinyl, pyridyl Base, pyrimidinyl, oxime Base, morpholinyl, imidazopyridyl, three Base, acridinyl, benzimidazolyl, benzo An azole group, a benzothiazolyl group, a bipyridyl group, a bipyridyl group, or the like, among the above heteroaryl groups, in one or more of the rings, as an atom other than carbon, having at least an aromaticity of an electron-accepting nitrogen atom Family heterocyclic group. In the compound having an electron-accepting nitrogen-containing aromatic heterocyclic group used in the present invention, the number of electron-accepting nitrogen contained in one aromatic heterocyclic ring is 1 to 3. However, a compound having an aromatic heterocyclic group containing an electron-accepting nitrogen may have four or more electron-accepting nitrogens in the case of a plurality of aromatic heterocyclic rings containing electron-accepting nitrogen. Among them, the aromatic heterocyclic group containing an electron-accepting nitrogen may have an alkyl group or a cycloalkyl group as a substituent.

A compound having an aromatic heterocyclic group containing an electron-accepting nitrogen is a single Compound, two Compound, and three In the case of the compound, electrons from the electron transport layer are easily received, and the electron injecting property to the light-emitting layer is increased, and the recombination probability is increased to improve the light-emitting efficiency.

When the compound having an aromatic heterocyclic group containing an electron-accepting nitrogen is a compound represented by the following formula (4), high electron injecting and transporting property is exhibited, so that luminous efficiency is improved. Further, since a stable film can be formed, it is preferable because the durability is improved.

In addition, when the substituent of the aromatic heterocyclic group containing electron-accepting nitrogen is a group represented by the following formula (4), high triplet state energy can be maintained. The level can achieve high luminous efficiency because it can suppress the activation without radiation. Further, the effect of suppressing the interaction between the molecules is increased, and a stable film can be formed, which is preferable because the durability is improved.

In the formula (4), R ⁵¹ to R ⁵⁵ and R ⁵⁶ to R ⁵⁷ each may be the same or different and are hydrogen, alkyl, cycloalkyl, heterocyclic, alkenyl, cycloalkenyl, alkynyl, alkane. Oxyl, alkylthio, aryl ether, aryl sulfide, aryl, heteroaryl, halogen, carbonyl, carboxyl, oxycarbonyl, aminecaraki, amine, or fluorenyl. Y ¹ is -N(R ⁵⁸ )-, -C(R ⁵⁹ R ⁶⁰ )-, an oxygen atom, or a sulfur atom. R ⁵⁸ to R ⁶⁰ each may be the same or different and are an alkyl group, an aryl group or a heteroaryl group. The adjacent substituents in R ⁵⁸ to R ⁶⁰ may form a ring with each other. L ² ~ L ⁴ is a single bond or an arylene group. X ¹ to X ⁵ represent a carbon atom or a nitrogen atom, and in the case where X ¹ to X ⁵ are a nitrogen atom, R ⁵¹ to R ⁵⁵ of the substituent on the nitrogen atom are not present. However, the number of nitrogen atoms in X ¹ to X ⁵ is 1 to 3. L ¹ is a single bond or an arylene group.

The arylene group of L ¹ to L ⁴ in the formula (4) refers to a divalent group formed by removing one hydrogen atom from two ring carbon atoms of an aromatic compound (aromatic hydrocarbon), and examples thereof include benzene stretching. Base, stretching naphthyl, stretching biphenyl, stretching fluorenyl, phenanthrene, and triphenyl. It may or may not have a substituent.

The description of the other substituents is the same as the compound represented by the formula (1).

The compound having a carbazole skeleton represented by the formula (4) is preferably an electron injection-transporting compound having an electron-accepting nitrogen-containing aromatic heterocyclic group, and is preferably contained by a carbazole skeleton. The dibenzofuran skeleton, the dibenzothiophene skeleton, the anthracene skeleton and the carbazole skeleton linkage of the condensed ring structure of Y ¹ are preferred because of excellent hole injection and transport properties. In the past, a compound having a carbazole skeleton does not necessarily have sufficient properties as a material of a light-emitting element. For example: 4,4'-bis(9H-carbazol-9-yl)-1,1'-biphenyl (abbreviation: CBP), and 1,3-bis(9H-carbazol-9-yl)benzene ( The abbreviation: mCP) is widely used as a material for a phosphorescent host material or an exciton blocking material, but it has a problem that the driving voltage becomes high regardless of which. In the improvement of the present invention, the inventors of the present invention have focused on the enhancement of the hole transporting ability and the electron transporting ability of the compound having a carbazole skeleton represented by the general formula (4). By using the compound having a carbazole skeleton represented by the general formula (4) as a host material of the light-emitting layer, the carrier from the hole transport layer and the electron transport layer in contact with the light-emitting layer can be efficiently received, and High luminous efficiency and low voltage effect. Further, by combining with a compound having a carbazole skeleton represented by the general formula (1), it is possible to block an excessive amount of the carrier, and it is possible to obtain a multiplication effect in which durability is improved.

Among the compounds having a carbazole skeleton represented by the formula (4), the linking position of the carbazole skeleton is preferably a compound represented by the formula (5).

In the general formula (5), R ⁵¹ to R ⁵⁷ and L ² to L ⁴ are the same as described above. R ⁶¹ is hydrogen, alkyl, cycloalkyl, heterocyclic, alkenyl, cycloalkenyl, alkynyl, alkoxy, alkylthio, aryl ether, aryl sulfide, aryl, heteroaryl, Halogen, carbonyl, carboxyl, oxycarbonyl, aminemethanyl, amine, or fluorenyl. L ¹ is an arylene group.

As in the compound represented by the above formula (5), the carbazoles are bonded to each other at the 3,3' position to form the same structure as the benzidine skeleton, and the hole transportability is further improved. Further, in the compound represented by the formula (5), if L ¹ is an arylene group, the electron transporting ability of the aromatic heterocyclic group containing electron-accepting nitrogen can be enhanced, and the light-emitting layer can be adjusted. The balance between the hole and the electron. Therefore, the luminous efficiency is improved due to an increase in the probability of recombination in the light-emitting layer.

Further, among the compounds having a carbazole skeleton represented by the formula (4), the linking position of the carbazole skeleton is preferably a compound represented by the formula (6) or (7). a compound represented by the following formula (6) or (7) In general, high film stability can be achieved by allowing the carbazoles to be asymmetrically linked to each other.

In the general formulae (4) to (7), L ² to L ^{4 are} preferably a single bond. By allowing L ² to L ^{4 to} be a single bond, the carbazole skeleton can be bonded to a dibenzofuran skeleton, a dibenzothiophene skeleton, an anthracene skeleton and a carbazole skeleton having a condensed ring structure containing Y ¹ . The hole transport characteristics improve the stability of the film quality. Further, in terms of availability of raw materials, R ⁵⁶ , R ⁵⁷ and R ^{61 are} preferably hydrogen.

In the general formulae (4) to (7), the number of nitrogen atoms in X ¹ to X ⁵ is 1 to 3, and among the X ¹ to X ⁵ , there are no nitrogen atoms adjacent to each other. The compound represented by the general formulae (4) to (7) does not have two nitrogen atoms adjacent to each other in X ¹ to X ⁵ , so that there is no heat-labile nitrogen-nitrogen double bond, so that the entire molecule The heat stability is improved. Further, it is easy to receive electrons from the electron transport layer, and since the electron injecting property to the light-emitting layer is high, it is preferable to increase the light-emitting efficiency by increasing the recombination probability.

Among them, in view of thermal stability and electron injection and transport characteristics, a compound represented by the general formulae (4) to (7) is more preferably a nitrogen atom of X ¹ , X ³ or X ⁵ .

In the general formulae (4) to (7), at least two of the R ⁵¹ to R ⁵⁵ are preferred because they can enhance the oxidation resistance of the ring structure containing X. More preferably, it is a phenyl group which can maintain a high triplet level.

The compound having an aromatic heterocyclic group containing an electron-accepting nitrogen may specifically be exemplified by the following compounds.

The compound represented by the formula (1) is preferably represented by the following formula (8) from the viewpoints of easiness of synthesis and hole transportability. It is shown that the carbazoles are linked to each other.

Further, from the viewpoint of improving the durability of the light-emitting element, an asymmetric carbazole dimer is preferred. This is because the symmetrical structure makes the crystallinity high, makes the film lack stability, and the durability of the element is lowered.

Specific examples of the compound represented by the formula (1) or (8) include the following compounds.

The compound represented by the formula (1) or (8) can be produced by a known method. That is, the bromide of the 9-substituted carbazole can be easily synthesized by the Suzuki coupling reaction of the 9-substituted carbazole, but the production method is not limited thereto.

Next, an embodiment of the light-emitting element of the present invention will be described in detail. The light-emitting element of the present invention has an anode and a cathode, and a hole transport layer and a light-emitting layer sandwiched between the anode and the cathode, and the light-emitting layer emits light by electric energy.

The layer structure between the anode and the cathode in such a light-emitting element, in addition to the structure formed by the hole transport layer and the light-emitting layer, may also be exemplified by the following laminated structure:

1) Hole transport layer / luminescent layer / electron transport layer

2) Hole injection layer / hole transport layer / luminescent layer / electron transport layer

3) hole transport layer / luminescent layer / electron transport layer / electron injection layer

4) Hole injection layer/hole transport layer/light emitting layer/electron transport layer/electron injection layer.

Each of the above layers may be a single layer or a plurality of layers, and may also be doped.

In the light-emitting element of the present invention, the anode and the cathode function to supply a sufficient current to cause the element to emit light, and at least one of them is desired to be transparent or translucent in order to extract light. The anode formed on the substrate is usually used as a transparent electrode.

In the light-emitting element of the present invention, the material used for the anode is capable of efficiently injecting holes into the material of the organic layer, and if it is transparent or translucent for light removal, zinc oxide, tin oxide, indium oxide, Conductive metal oxides such as indium tin oxide (ITO) and indium zinc oxide (IZO), or metals such as gold, silver, and chromium, inorganic conductive materials such as copper iodide and copper sulfide, polythiophene, polypyrrole, polyaniline, etc. The conductive polymer or the like is not particularly limited, but it is particularly preferable to use ITO glass or Nesep glass. These electrode materials may be used singly or in combination of a plurality of materials. The electric resistance of the transparent electrode is not limited as long as it can supply sufficient electric power to cause the element to emit light, but it is desirably low in resistance from the viewpoint of power consumption of the element. For example, an ITO substrate of 300 Ω/□ or less can be used as an element electrode. However, since a substrate of about 10 Ω/□ can be provided, it is particularly preferable to use a substrate having a low resistance of 20 Ω/□ or less. The thickness of the ITO can be arbitrarily selected depending on the resistance value, and is usually used in a range of 50 to 300 nm.

Further, in order to maintain the mechanical strength of the light-emitting element, it is preferred to form a light-emitting element on the substrate. A glass substrate such as soda glass or alkali-free glass is preferably used as the substrate. The thickness of the glass substrate is sufficient as long as it is a mechanical strength, and therefore 0.5 mm or more is sufficient. As for the material of the glass, since the amount of ions eluted from the glass is preferably small, it is preferably an alkali-free glass. Alternatively, a soda lime glass to which a barrier coating such as SiO ₂ is applied can be used because it is commercially available. Further, as long as the first electrode can be stabilized, the substrate does not have to be glass, and for example, an anode can also be formed on the plastic substrate. The method of forming the ITO film is not particularly limited by an electron beam method, a sputtering method, a chemical reaction method, or the like.

In the light-emitting element of the present invention, the material used for the cathode is not particularly limited as long as it can efficiently inject electrons into the light-emitting layer. Generally, 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 are preferable. Among them, aluminum, silver, and magnesium are preferable as the main component in terms of resistance value, easiness of film formation, stability of film, and luminous efficiency. In particular, when it is composed of magnesium and silver, electrons are easily injected into the electron transport layer and the electron injection layer of the present invention, and it is preferable to realize low voltage driving.

Further, in order to protect the cathode, a metal such as platinum, gold, silver, copper, iron, tin, aluminum, or indium, or an alloy using these metals, cerium oxide, titanium oxide, and tantalum nitride may be mentioned. An inorganic substance, an organic polymer compound such as polyvinyl alcohol, polyvinyl chloride or a hydrocarbon-based polymer compound is laminated on the cathode as a protective film layer. However, in the case of the element structure (top emission structure) in which light is taken out from the cathode side, the protective film layer is selected from materials having light transmissivity in the visible light region. The fabrication of these electrodes is not particularly limited to resistance heating, electron beam, Sputtering, ion plating and coating.

In the light-emitting element of the present invention, the hole injection layer is interposed between the anode and the hole transport layer. The hole injection layer is one layer or a plurality of layers. If a hole injection layer exists between the hole transport layer and the anode, not only can it be driven at a lower voltage, but the durability life is improved, which is better because the carrier balance of the element is further improved and the luminous efficiency is also improved.

The material used for the hole injection layer is not particularly limited, and for example, 4,4'-bis(N-(3-methylphenyl)-N-phenylamine)biphenyl (TPD), 4, 4' can be used. - bis(N-(1-naphthyl)-N-phenylamine)biphenyl (NPD), 4,4'-bis(N,N-bis(4-biphenyl)amino)biphenyl (TBDB) ), bis(N,N'-diphenyl-4-aminophenyl)-N,N-diphenyl-4,4'-diamino-1,1'-biphenyl (TPD232), 4 , 4',4"-parade (3-methylphenyl(phenyl)amino)triphenylamine (m-MTDATA), 4,4',4"-paran (1-naphthyl (phenyl) An arylamine derivative such as an amino)triphenylamine (1-TNATA), a pyrazoline derivative, an anthraquinone compound, an anthraquinone compound, a benzofuran derivative, a thiophene derivative, a heterocyclic compound such as an oxadiazole derivative, an anthraquinone derivative or a porphyrin derivative, and a polymer system can be used for a polycarbonate or a styrene derivative having a side chain having the aforementioned monomer, polythiophene, polyaniline, polyfluorene , polyvinyl carbazole and polydecane. The compound represented by the general formula (1) or (8) can also be used for the hole injection layer, and also has a shallow HOMO energy level, from the viewpoint that the anode is smoothly injected into the hole transport layer from the anode. Better to use.

These materials may be used singly or in combination of two or more materials. Further, a plurality of material layers may be laminated as a hole injection layer. Further, if the hole injection layer is formed of an acceptor material alone or is doped with an acceptor material as described above, the above effect is more remarkable and more preferable. The acceptor material, when used as a single layer film, forms a charge transporting compound material with the contact hole transport layer, and forms a charge with the material constituting the hole injection layer in the case of doping. Move the material of the complex. When such a material is used, the conductivity of the hole injection layer is increased, which contributes to further lowering the driving voltage of the element, thereby improving the luminous efficiency and improving the durability life.

Examples of the acceptor material include iron chloride (III), aluminum chloride, gallium chloride, indium chloride, and metal chloride of barium chloride, such as molybdenum oxide, vanadium oxide, tungsten oxide, and barium oxide. A metal oxide such as a charge shift complex of hexachloroantimonate (4-bromophenyl) ammonium (TBPAH). Further, it is also suitably used for an organic compound having a nitro group, a cyano group, a halogen or a trifluoromethyl group in the molecule, or an anthraquinone compound, an acid anhydride compound, a fullerene or the like. Specific examples of such a compound include hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane (TCNQ), tetrafluorotetracyanoquinodimethane (F4-TCNQ), Aromatic derivatives, tetrafluorop-benzoquinone, tetrachloro-p-benzoquinone, tetrabromo-p-benzoquinone, p-benzoquinone, 2,6-dichlorophenylhydrazine, 2,5-dichlorophenylhydrazine, tetramethylphenylhydrazine 1,2,4,5-tetracyanobenzene, o-dicyanobenzene, p-dicyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5,6-dicyandi Benzoquinone, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, p-cyanonitrobenzene, m-cyanonitrobenzene, o-cyanonitrobenzene, 1,4-naphthoquinone, 2,3-Dichloronaphthylquinone, 1-nitronaphthalene, 2-nitronaphthalene, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene, 9-cyanoguanidine, 9-nitroguanidine , 9,10-蒽醌, 1,3,6,8- Tetranitrocarbazole, 2,4,7-trinitro-9-fluorenone, 2,3,5,6-tetracyanopyridine, maleic anhydride, fumaric anhydride, C60, and C70 Wait.

Among these, the metal oxide and the compound containing a cyano group are easily vapor-deposited because of easy handling, and it is preferable to easily obtain the above effects. In either case where the hole injection layer is composed of an acceptor material alone or in the case where the hole injection layer is doped with an acceptor material, the hole injection layer may be one layer, It can be composed of multiple layers.

The acceptor material is not particularly limited, but is preferably in the range of 0.1 to 50 parts by mass, more preferably 0.5 to 20 parts by mass, based on the compound represented by the formula (1) or (8). use.

In the light-emitting element of the present invention, the hole transport layer transports the holes injected from the anode to the layers of the light-emitting layer. The compound represented by the formula (1) or (8) is suitably used as a hole transport layer of a light-emitting element because of its high triplet energy level, high hole transport property, and film stability. The hole transport layer may be a single layer or a plurality of layers, and any of them may be used.

In the case where the plurality of layers of the hole transport layer are formed, it is preferred that the hole transport layer containing the compound represented by the formula (1) or (8) is in direct contact with the light-emitting layer. The compound represented by the formula (1) or (8) has high electron blocking property and can prevent entry of electrons flowing out of the light-emitting layer. Further, since the compound represented by the general formula (1) or (8) has a high triplet energy level, it also has an effect of blocking the excitation energy of the triplet luminescent material. Therefore, in the case where the light-emitting layer contains a triplet light-emitting material, the hole transport layer containing the compound represented by the general formula (1) preferably has direct contact with the light-emitting layer.

The hole transport layer may be composed only of the compound represented by the general formula (1) or (8), and other materials may be mixed in a range not impairing the effects of the present invention. In this case, the material used in the hole injection layer and the same material group can be preferably exemplified, and in the case of using the hole transport layer, it is better to select and use it in the hole injection layer. A material with the same or a deeper HOMO level than the material. In this case, other materials used may, for example, be 4,4'-bis(N-(3-methylphenyl)-N-phenylamine)biphenyl (TPD), 4,4'-double (N-(1-naphthyl)-N-phenylamine)biphenyl (NPD), 4,4'-bis(N,N-bis(4-biphenyl)amino)biphenyl (TBDB), Derivative of benzidine such as bis(N,N'-diphenyl-4-aminophenyl)-N,N-diphenyl-4,4'-diamino-1,1'-biphenyl (TPD232) , 4,4',4"-gin(3-methylphenyl(phenyl)amino)triphenylamine (m-MTDATA), 4,4',4"-paran (1-naphthyl ( Phenyl)amino)triphenylamine (1-TNATA), a group of materials known as starburst arylamines, bis(N-arylcarbazole) or bis(N-alkylcarbazole) a biscarbazole derivative, a pyrazoline derivative, an anthraquinone compound, an anthraquinone compound, a benzofuran derivative, a thiophene derivative, a heterocyclic compound such as an oxadiazole derivative, an anthraquinone derivative or a porphyrin derivative, and the polymer system may be a polycarbonate or a styrene derivative having a monomer in the side chain, polythiophene, polyaniline, or poly Antimony, polyvinyl carbazole and polydecane.

In the light-emitting device of the present invention, the light-emitting layer may be a single layer or a plurality of layers. In the case where the light-emitting layer is a plurality of layers, each of the light-emitting layers is formed by a light-emitting material (host material, dopant material), and each light-emitting layer is a mixture of the host material and the dopant material, a single host material, or two kinds. A mixture of the host material and one dopant material can be used. That is, in the light-emitting element of the present invention, only the light-emitting layers may be used only The host material can be illuminated by the host material or only by the dopant material, or the host material can be illuminated with the dopant material. From the viewpoint of efficiently utilizing electric energy and obtaining luminescence of high color purity, the luminescent layer is preferably composed of a mixture of a host material and a dopant material. Further, the host material and the dopant material may each be a single type or a combination of a plurality of types, and either one may be used. The dopant material may be included in the entirety of the host material, and may be included in part or in whichever. The dopant material can be layered or dispersed, and either one can be used. The dopant material controls the luminescent color. If the amount of the dopant material is too large, the concentration quenching phenomenon is caused, and it is preferably 30% by mass or less, and more preferably 20% by mass or less based on the host material. The doping method can be formed by a co-evaporation method with the host material, or can be previously vapor-deposited after mixing with the host material.

A compound having an aromatic heterocyclic group containing electron-accepting nitrogen is suitable for use as a light-emitting layer of a light-emitting element because of its high electron transport property and film stability. On the other hand, a compound having an aromatic heterocyclic group containing an electron-accepting nitrogen is preferably used for a host material because of its high electron transport property and film stability.

Further, since a compound having an aromatic heterocyclic group containing an electron-accepting nitrogen has a high triplet energy level, it is preferably used as a host material of an element using a triplet light-emitting material. Further, as the compound having an aromatic heterocyclic group containing an electron-accepting nitrogen, a compound represented by the general formulae (4) to (7) is particularly preferable.

In the light-emitting device of the present invention, in addition to the compound having an electron-accepting nitrogen-containing aromatic heterocyclic group, a condensed ring derivative such as ruthenium and osmium which has been known as an illuminant in the past may be used as the luminescent material. Metal chelating oxinoid compounds led by hydroxyquinoline aluminum, bisstyryl derivatives such as bisstyryl fluorene derivatives and distyrylbenzene derivatives, tetraphenylbutadiene derivatives , anthracene derivatives, coumarin derivatives, An oxadiazole derivative, a pyrrolopyridinium derivative, a benzalkonone derivative, a cyclopentadiene derivative, An oxadiazole derivative, a thiadiazole pyridine derivative, a dibenzofuran derivative, a carbazole derivative, a carbazole derivative, and a polyphenylene extending ethylene derivative and a polyparaphenylene benzene can be used in the polymer system. The derivative, the polythiophene derivative, and the like are not particularly limited.

The host material contained in the luminescent material is not limited to a single compound, and a plurality of compounds may be mixed with the compounds represented by the general formulae (4) to (7), or the general formula (4) to (7) may be used. The compound represented is used in combination with other host materials. Further, a plurality of compounds represented by the general formulae (4) to (7) may be used in a layered manner, or a compound represented by the general formulae (4) to (7) may be laminated with another host material. Other host materials are not particularly limited and can be used: naphthalene, anthracene, phenanthrene, anthracene, (chrysene), tetracene, triphenylene, anthracene, benzopyrene, anthracene, anthracene, etc., compounds having a condensed aryl ring and derivatives thereof, N,N'-dinaphthyl-N,N'-diphenyl An aromatic amine derivative such as a 4,4'-diphenyl-1,1'-diamine, a metal chelate-based oxin compound headed by bis(8-hydroxyquinoline)aluminum (III), a bisstyryl derivative such as a styrylbenzene derivative, a tetraphenylbutadiene derivative, an anthracene derivative, a coumarin derivative, An oxadiazole derivative, a pyrrolopyridinium derivative, a benzalkonone derivative, a cyclopentadiene derivative, a pyrrolopyrrole derivative, a thiadiazolopyridine derivative, a dibenzofuran derivative, a carbazole derivative, Carbazole derivatives, three As the derivative or the polymer system, a polyphenylene stretched ethylene derivative, a polyparaphenylene derivative, a polyfluorene derivative, a polyvinylcarbazole derivative, a polythiophene derivative or the like can be used, but is not limited thereto. Among them, the main body used in the triplet emission (phosphorescence) of the light-emitting layer is preferably used: a metal chelate-based octyl compound, a dibenzofuran derivative, a dibenzothiophene derivative, a carbazole derivative, Carbazole derivatives, three Derivatives, triazine derivatives, and the like.

The dopant material contained in the luminescent material is not particularly limited, and examples thereof include a compound having an aryl ring such as naphthalene, anthracene, phenanthrene, anthracene, hydrazine, anthracene, anthracene, anthracene, and the like (for example, 2) -(Benzothiazol-2-yl)-9,10-diphenylanthracene and 5,6,11,12-tetraphenylthincene tetraphenyl, etc., furan, pyrrole, thiophene, silole, 9 - hydrazine, 9,9'-spirobioxazepine, benzothiophene, benzofuran, anthracene, dibenzothiophene, dibenzofuran, imidazopyridine, phenanthroline, pyridinium , Pyridine Porphyrin, pyrrolopyridine, sulfur a compound having a heteroaromatic ring and a derivative thereof, a distyrylbenzene derivative, 4,4'-bis(2-(4-diphenylaminophenyl)vinyl)biphenyl, 4,4'-double Aminostyryl derivative such as (N-(indol-4-yl)-N-phenylamine) hydrazine, aromatic acetylene derivative, tetraphenylbutadiene derivative, anthracene derivative, aldehyde nitrogen ( Aldazine) derivative, pyrromethene derivative, pyrrolo[3,4-c]pyrrolidone derivative, 2,3,5,6-1H,4H-tetrahydro-9-(2' -benzothiazolyl)quine [9,9a,1-gh] coumarin derivatives such as coumarin, imidazole, thiazole, thiadiazole, carbazole, Azole, An azole derivative such as oxadiazole or triazole and a metal complex thereof, and N,N'-diphenyl-N,N'-bis(3-methylphenyl)-4,4'-diphenyl An aromatic amine derivative represented by a -1,1'-diamine.

The dopant used in the triplet luminescence (phosphorescence) of the luminescent layer preferably contains at least one kind of ruthenium (Ir), ruthenium (Ru), palladium (Pd), platinum (Pt), ruthenium. A metal complex compound of a metal selected from the group consisting of (Os) and ruthenium (Re). The ligand is preferably a nitrogen-containing aromatic heterocyclic ring such as a phenylpyridine skeleton, a phenylquinoline skeleton or a carbene skeleton. However, it is not limited thereto, and a suitable complex compound can be selected from the desired luminescent color, element performance, and relationship with the host compound. Specific examples include ginseng (2-phenylpyridine) ruthenium complex, ginseng [2-(2-phenylthio)pyridine] ruthenium complex, and ginseng [2-(2-benzophenyl sulphide). Pyridine] ruthenium complex, ginseng (2-phenylbenzothiazole) ruthenium complex, ginseng (2-phenylbenzophenone) Oxazole) hydrazine complex, benzoquinoline quinone complex, bis(2-phenylpyridine) (acetamidine) ruthenium complex, bis[2-(2-phenylthio)pyridine] Compound, bis[2-(2-benzophenylthio)pyridine](acetamidineacetone) ruthenium complex, bis(2-phenylbenzothiazole) (acetamidineacetone) ruthenium complex, bis ( 2-phenylbenzo Oxazole) (acetamidine) ruthenium complex, bisbenzoquinoline (acetamidine) ruthenium complex, bis[2-(2,4-difluorophenyl)pyridine] (acetamidine) Compound, tetraethylporphyrin platinum complex, [((thiophenemethyl trifluoroacetone) mono(1,10-morpholine)] ruthenium complex, [paraxyl (thiophenemethyl trifluoroacetone)] Mono(4,7-diphenyl-1,10-morpholine)] ruthenium complex, [gin(1,3-diphenyl-1,3-propanedione) mono (1,10-morpholine) )] 铕 complex, acetyl acetoxime complex and the like. Further, a phosphorescent dopant described in JP-A-2009-130141 is also applicable. Although it is not limited to this, it is preferable to use a ruthenium complex or a platinum complex from the viewpoint of easily obtaining high-efficiency light emission.

The above triplet luminescent material as the dopant material may be used alone or in combination of two or more kinds in the light-emitting layer. When two or more triplet luminescent materials are used, the total mass of the dopant material is preferably 30% by mass or less, more preferably 20%, based on the host material. Below mass%. Preferred examples of the dopant include the following examples.

Further, in addition to the above-described host material and triplet light-emitting material, the light-emitting layer adjusts the balance of the carrier in the light-emitting layer, or stabilizes The purpose of the layer structure of the light-emitting layer may also include the third component. Specifically, the following examples are mentioned.

In the light-emitting element of the present invention, the electron transport layer injects electrons from the cathode and further transports the electron layer. The desired electron injection efficiency for the electron transport layer is high and the injected electrons can be efficiently transported. Therefore, the electron transport layer is required to have a large electron affinity, a large electron mobility, and excellent stability, and it is difficult to produce a substance which becomes a trap impurity at the time of manufacture and use. In particular, in the case of a thick film thickness, a compound having a low molecular weight tends to deteriorate the film quality due to crystallization or the like. Therefore, a compound having a molecular weight of 400 or more which maintains a stable film quality is preferable. however, Considering the balance of the transport of holes and electrons, the electron transporting layer is not so high even if it is capable of effectively preventing the flow to the cathode side without recombination with the holes from the anode. The material composition is such that the effect of improving the luminous efficiency is also the same as that of the material having high electron transporting ability. Therefore, the electron transport layer in the present invention also includes a substance synonymous with a hole stop layer capable of efficiently preventing the movement of holes.

Examples of the electron transporting material used in the electron transporting layer include a condensed polycyclic aromatic derivative such as naphthalene or an anthracene, and a styrene-based aromatic ring represented by 4,4'-bis(diphenylvinyl)biphenyl. Derivatives, anthraquinone derivatives such as hydrazine and biphenyl hydrazine, phosphine oxide derivatives, hydroxyquinoline complexes such as quinone (8-hydroxyquinoline) aluminum (III), benzoquinoline complex, hydroxyazole Various metal complexes such as a complex, a methylimine complex, a phenol ketone metal complex, and a flavonol metal complex. The electron transporting material used in the electron transporting material of the present invention preferably has electron-accepting nitrogen and carbon, hydrogen, nitrogen, oxygen, helium, and phosphorus from the viewpoint of reducing the driving voltage and obtaining high-efficiency light emission. A compound of an aromatic heterocyclic structure composed of the selected elements.

The electron-accepting nitrogen referred to herein means a nitrogen atom which forms a multiple bond between adjacent atoms. Since the nitrogen atom has a high electronegativity, the multiple bond has the property of accepting electrons. Therefore, the aromatic heterocyclic ring containing electron-accepting nitrogen has high electron affinity. An electron transporting material having electron-accepting nitrogen readily accepts electrons from a cathode having high electron affinity and can be driven at a lower voltage. Further, the amount of electrons supplied to the light-emitting layer is increased, and the luminous efficiency is improved because the probability of recombination is increased.

Examples of the heteroaryl ring containing electron-accepting nitrogen include a pyridine ring and a pyridyl group. Ring, pyrimidine ring, quinoline ring, quin Porphyrin ring, a pyridine ring, a pyrimidopyrimidine ring, a benzoquinoline ring, a phenanthroline ring, an imidazole ring, Oxazole ring, Diazole ring, triazole ring, thiazole ring, thiadiazole ring, benzo An azole ring, a benzothiazole ring, a benzimidazole ring, a phenanthrene-imidazole ring, and the like.

Preferred compounds of these compounds having a heteroaromatic ring structure include, for example, benzimidazole derivatives, benzo An azole derivative, a benzothiazole derivative, Diazole derivatives, thiadiazole derivatives, triazole derivatives, pyridyl Derivatives, phenanthroline derivatives, quinolin Oligopyridine derivatives such as porphyrin derivatives, quinoline derivatives, benzoquinoline derivatives, bipyridine and terpyridine, quinolin Porphyrin derivative and Pyridine derivatives and the like. Among them, from the viewpoint of electron transporting ability, an imidazole derivative such as ginseng (N-phenylbenzimidazol-2-yl)benzene or 1,3-bis[(4-tributylphenyl) is preferably used. )-1,3,4- Diazolyl] Diazole derivatives, triazole derivatives such as N-naphthyl-2,5-diphenyl-1,3,4-triazole, bathocuproine and 1,3-double (1,10-morphine) Phenanthroline derivative such as porphyrin-9-yl)benzene, benzoquinoline derivative such as 2,2'-bis(benzo[h]quinolin-2-yl)-9,9'-spirobifluorene, 2 , 5-bis(6'-(2',2"-bipyridyl))-1,1-dimethyl-3,4-diphenylthiazole, etc., dipyridine derivative, 1,3-double (4 '-(2,2':6'2"-terpyridine)) a terpyridine derivative such as benzene, bis(1-naphthyl)-4-(1,8- Pyridin-2-yl)phenylphosphine Pyridine derivatives. Further, when these derivatives have a condensed polycyclic aromatic skeleton, the glass transition temperature is increased, and the electron mobility is also increased, and the effect of lowering the voltage of the light-emitting element is further improved. Further, in consideration of the durability of the lifting element, the ease of synthesis, and the availability of the raw material, the condensed polycyclic aromatic skeleton is particularly preferably an anthracene skeleton, an anthracene skeleton or a phenanthroline skeleton. The electron transporting material may be used alone or in combination of two or more kinds of the above-described electron transporting materials, or may be used by mixing one or more other electron transporting materials with the above-described electron transporting materials.

The preferred electron transporting material is not particularly limited, and specific examples thereof are as follows.

The above electron transporting materials may be used singly or in combination with a bulk material. Here, the host material is a compound which facilitates electron injection from the cathode or the electron injecting layer to the electron transporting layer by improving the electron injecting barrier, and further enhances the conductivity of the electron transporting layer.

Preferable examples of the host material include an alkali metal, an inorganic salt containing an alkali metal, a complex of an alkali metal and an organic substance, an alkaline earth metal, an inorganic salt containing an alkaline earth metal, or a complex of an alkaline earth metal and an organic substance. . Preferred examples of the alkali metal and the alkaline earth metal include alkali metals such as lithium, sodium, potassium, rubidium, and cesium which have a low work function and an improved electron transporting ability. With alkaline earth metals such as magnesium, calcium, strontium and barium.

Further, from the viewpoint of easy vapor deposition in a vacuum and easy handling, it is preferably a state of an inorganic salt or a complex with an organic substance as compared with a metal monomer. Further, in the case where it is easy to handle in the atmosphere, and the concentration at which the concentration is easily controlled is more preferable, it is a state of a complex with an organic substance. Examples of the inorganic salt include oxides such as LiO and Li ₂ O, nitrides, fluorides such as LiF, NaF, and KF, Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , and Cs. ₂ Carbonate such as CO ₃ . Preferred examples of the alkali metal or alkaline earth metal include lithium and bismuth from the viewpoint of obtaining a large low-voltage driving effect. Preferable examples of the organic substance in the organic substance and the complex compound include hydroxyquinoline, benzoquinoline, pyridylphenol, flavonol, hydroxyimidazopyridine, hydroxybenzoxazole, hydroxytriazole and the like. In view of the fact that the effect of lowering the voltage of the light-emitting element is greater, it is preferably a complex of an alkali metal and an organic substance, and further preferably from the viewpoints of ease of synthesis, thermal stability, and the like. A complex of lithium and an organic compound, and particularly preferably a lithium hydroxyquinolate which can be obtained relatively inexpensively.

The ionization potential of the electron transport layer is not particularly limited, but is preferably 5.6 eV or more and 8.0 eV or less, and more preferably 6.0 eV or more and 7.5 eV or less.

The method of forming the respective layers constituting the light-emitting element is not particularly limited to resistance heating deposition, electron beam evaporation, sputtering, molecular lamination, coating, etc., and generally, resistance heating is preferred in terms of device characteristics. Evaporation or electron beam evaporation.

In the light-emitting device of the present invention, the thickness of the organic layer in each of the above layers is not limited because it depends on the resistance value of the light-emitting substance, but It is preferably 1 to 1000 nm. The film thickness of the light-emitting layer, the electron transport layer, and the hole transport layer is preferably 1 nm or more and 200 nm or less, and more preferably 5 nm or more and 100 nm or less.

The light-emitting element of the present invention has a function of converting electrical energy into light. The electric energy here mainly uses direct current, but pulse current and alternating current can also be used. The current value and the voltage value are not particularly limited, but if the power consumption and life of the component are considered, the maximum brightness should be selected with low energy as much as possible.

The light-emitting element of the present invention can be applied to displays that are displayed, for example, in a matrix and/or node type.

In the light-emitting element of the present invention, the matrix type means that the pixel system for display is arranged in a lattice shape or a mosaic shape of a two-dimensional element, and characters or images are displayed in a set of pixels. The shape and size of the pixels are determined by the application. For example, for images and text display on computers, monitors, and televisions, quadrangular pixels of 300 μm or less per side are usually used, and in the case of a large display such as a display panel, pixels of each order of mm are used. In the case of monochrome display, pixels of the same color may be arranged, and in the case of color display, red, green, and blue pixels are displayed side by side. In this case, there are typically a delta type and a stripe type. The driving method of this matrix is either a progressive driving method or an active matrix. Although the progressive drive has a simple structure, in consideration of the behavior characteristics, there is also a case where the active matrix is superior, and it is also necessary to use it according to the use.

In the light-emitting element of the present invention, the node type means that a pattern is formed in such a manner as to display predetermined information, and is determined according to the arrangement of the pattern. The way the area shines. For example, a time and temperature display in a digital clock and a thermometer, an operation state display such as an audio-visual equipment and an induction cooker, and a panel display of a car can be cited. In addition, the aforementioned matrix display and node display can also be stored in the same panel.

The light-emitting element of the present invention can be preferably used as a backlight of various machines and the like. The main purpose of the backlight is to improve the visibility of the display that does not self-illuminate, and is used for liquid crystal display devices, clocks, audio-visual equipment, automobile panels, display panels, and signs. The light-emitting element of the present invention can be preferably used for a liquid crystal display device, particularly a backlight for a computer application in which thinness is desired, and can provide a thinner and lighter backlight than in the past.

[Examples]

The following examples are provided to illustrate the invention, but the invention is not limited by the examples.

Example 1

A glass substrate (manufactured by Geomatec, 11 Ω/□, sputtering product) on which a 50 nm ITO transparent conductive film was deposited was cut into 38×46 mm, and etched. The obtained substrate was subjected to ultrasonic cleaning for 15 minutes under "Semico Clean 56" (trade name, manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water. The substrate was subjected to U V-ozone treatment for 1 hour before the fabrication of the device, and was placed in a vacuum evaporation apparatus, and the degree of vacuum exhausted into the apparatus was 5 × 10 ^-4 Pa. Then, 10 nm of HI-1 as a hole injection layer was vapor-deposited on the substrate by a resistance heating method. Next, 100 nm was deposited as the NPD of the first hole transport layer. Next, 20 nm of HT-1 as a second hole transport layer was vapor-deposited. Next, as the light-emitting layer, Compound H-1 was used as a host material, and Compound D-1 was used as a dopant material, and the dopant concentration of the dopant material was 5% by mass, and the thickness was vapor-deposited to 40 nm. Next, as the electron transport layer, a compound E-1 having a thickness of 20 nm was laminated.

Next, 0.5 nm of lithium fluoride and 60 nm of aluminum were vapor-deposited to form a 5×5 mm square element. Here, the film thickness is a quartz oscillation type film thickness monitor display value. When the light-emitting element was driven at a direct current of 10 mA/cm ² , green light emission having a luminous efficiency of 26.01 m/W was obtained. When the light-emitting element was continuously driven at a direct current of 10 mA/cm ² , the luminance was halved at 2700 hours. Among them, the compounds NPD, HI-1, HT-1, H-1, D-1, and E-1 are shown below.

Example 2~9

A light-emitting device was produced in the same manner as in Example 1 except that the material described in Table 1 was used as the second hole transport layer, the host material, and the dopant material. The results of the respective examples are shown in Table 1. among them, HT-2~HT-4, H-2~H-4, D-2, and D-3 are compounds shown below.

Comparative example 1~8

A light-emitting device was produced in the same manner as in Example 1 except that the material described in Table 1 was used as the second hole transport layer, the host material, and the dopant material. The results of the respective examples are shown in Table 1. among them, The compounds are shown below in HT-5~HT-8 and H-5~H-7.

Example 10

In addition to using the material described in Table 1 as an electron transporting material and substituting the compound E-1, the compound E-1 and the host material were used at a vapor deposition rate ratio of 100:1 (=0.2 nm/s: 0.002 nm/s). A light-emitting device was produced in the same manner as in Example 1 except for the co-deposited film of (Li: lithium). The results are shown in Table 1.

Example 11

Except that the material described in Table 1 was used as the electron transport layer, the electron transport layer was formed by two layers, and the compound E-2 having a thickness of 10 nm was vapor-deposited as the first electron transport layer, and the vapor deposition rate ratio was 100:1 (=0.2). Nm/s: 0.002 nm/s) A vapor-deposited film of a compound E-1 having a thickness of 25 nm and a host material (Cs ₂ CO ₃ : cesium carbonate) was deposited as a second electron transport layer, and Example 1 was carried out. In the same manner, a light-emitting element was produced. The results are shown in Table 1. Among them, E-2 is a compound shown below.

Example 12

In addition to using the material described in Table 1 as the electron transport layer and substituting the compound E-1, the compound E-3 and the host material were used at a vapor deposition rate ratio of 1:1 (=0.05 nm/s: 0.05 nm/s). A light-emitting device was produced in the same manner as in Example 1 except that the film was deposited (Liq: lithium hydroxyquinolate). Knot The results are shown in Table 1. Among them, E-3 is a compound shown.

Example 13

In addition to using the material described in Table 1 as the electron transport layer and substituting the compound E-1, the compound E-4 and the host material were used at a vapor deposition rate ratio of 1:1 (=0.05 nm/s: 0.05 nm/s). A light-emitting device was produced in the same manner as in Example 1 except for the co-deposited film of (LiF: lithium fluoride). The results are shown in Table 1. Among them, E-4 is a compound shown.

Example 14

A light-emitting device was produced in the same manner as in Example 1 except that the material described in Table 1 was used as the electron transport layer. The results are shown in Table 1. Among them, E-5 is a compound shown.

Example 15

A glass substrate (manufactured by Geomatec, 11 Ω/□, sputtering product) on which a 50 nm ITO transparent conductive film was deposited was cut into 38×46 mm, and etched. The obtained substrate was subjected to ultrasonic cleaning for 15 minutes under "Semico Clean 56" (trade name, manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water. The substrate was subjected to U V-ozone treatment for 1 hour before the fabrication of the device, and was placed in a vacuum evaporation apparatus, and the degree of vacuum exhausted into the apparatus was 5 × 10 ^-4 Pa. Then, 10 nm of HI-1 as a hole injection layer was vapor-deposited on the substrate by a resistance heating method. Next, 100 nm was deposited as HT-8 as the first hole transport layer. Next, 50 nm of HT-1 as a second hole transport layer was deposited. Next, as the light-emitting layer, Compound H-8 was used as a host material, and Compound D-4 was used as a dopant material, and the dopant concentration of the dopant material was 3% by mass, and the thickness was vapor-deposited to 30 nm. Next, as the electron transport layer, a compound E-1 having a thickness of 35 nm was laminated.

Next, 0.5 nm of lithium fluoride and 1000 nm of aluminum were vapor-deposited as a cathode to prepare a 5×5 mm square element. Here, the film thickness is a quartz oscillation type film thickness monitor display value. When the light-emitting element was driven at a direct current of 10 mA/cm ² , high-efficiency red light emission having a luminous efficiency of 13.01 m/W was obtained. When the light-emitting element was continuously driven at a direct current of 10 mA/cm ² , the luminance was halved at 3,300 hours. Among them, the compounds H-8 and D-4 are shown below.

Example 16~21

A light-emitting device was produced and evaluated in the same manner as in Example 15 except that the material described in Table 2 was used as the second hole transport layer. The results are shown in Table 2. Among them, the compounds HT-9 and HT-10 are shown below.

Comparative Example 9~11

A light-emitting device was produced and evaluated in the same manner as in Example 15 except that the material described in Table 2 was used as the second hole transport layer and the host material. The results are shown in Table 2. Among them, the compounds HT-11 and H-9 are shown below.

Example 22~23

A light-emitting device was produced and evaluated in the same manner as in Example 15 except that the material described in Table 2 was used as the second hole transport layer and the electron transport material. The results are shown in Table 2.

Examples 24 to 31

A light-emitting device was produced and evaluated in the same manner as in Example 15 except that the material described in Table 2 was used as the second hole transport layer and the host material. The results are shown in Table 2. Among them, compounds H-10 to H-17 are shown below.

Claims (12)

A light-emitting element comprising at least a hole transport layer and a light-emitting layer between an anode and a cathode, and a light-emitting element that emits light by electric energy, wherein the hole transport layer is represented by the following general formula (1) The compound, wherein the light-emitting layer has a compound containing an electron-accepting nitrogen-containing aromatic heterocyclic group, and comprises a compound represented by the following formula (4): (In the formula (1), each of R ³ to R ¹⁸ may be the same or different and is derived from hydrogen, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, or an alkane. Thio group, aryl ether group, aryl sulfide group, aryl group, heteroaryl group, halogen, carbonyl group, carboxyl group, oxycarbonyl group, amine mercapto group, amine group, fluorenyl group, -P(=O)R ¹⁹ R ²⁰ Selected as a group; R ¹⁹ and R ²⁰ are aryl or heteroaryl; L is a single bond, arylene or heteroarylene; but the two carbazole skeletons are in R ⁷ ~ R ¹⁰ , R Any one of ¹¹ to R ¹⁴ is bonded to L; wherein R ¹ to R ¹⁸ are excluding a dibenzofuran skeleton, a dibenzothiophene skeleton, and a carbazole skeleton; and R ¹ is a compound of the following formula (2) The base expressed; In the formula (2), each of R ²¹ to R ²⁵ may be the same or different and is hydrogen, or an aryl group having a substituent or a substituent; but at least two of R ²¹ to R ²⁵ have a substituent or no The aryl group of the substituent is composed only of an aromatic hydrocarbon; and R ² is a group represented by the following formula (3); In the formula (3), each of R ²⁶ to R ³⁰ may be the same or different, and is a hydrogen or a substituted or unsubstituted aryl group, which is composed only of an aromatic hydrocarbon; In the formula (4), R ⁵¹ to R ⁵⁵ and R ⁵⁶ to R ⁵⁷ each may be the same or different, and are hydrogen, alkyl, cycloalkyl, heterocyclic, alkenyl, cycloalkenyl, alkynyl, Alkoxy, alkylthio, aryl ether, aryl sulfide, aryl, heteroaryl, halogen, carbonyl, carboxyl, oxycarbonyl, aminecardenyl, amine, or fluorenyl; Y ¹ - N(R ⁵⁸ )-, -C(R ⁵⁹ R ⁶⁰ )-, an oxygen atom, or a sulfur atom; each of R ⁵⁸ to R ⁶⁰ may be the same or different and is an alkyl group, an aryl group, or a heteroaryl group; R ⁵⁸ The substituents adjacent to ~R ⁶⁰ may form a ring with each other; L ² ~ L ⁴ are a single bond or an arylene group; X ¹ ~ X ⁵ are carbon atoms or nitrogen atoms, and X ¹ ~ X ⁵ are nitrogen In the case of an atom, R ⁵¹ to R ⁵⁵ of the substituent on the nitrogen atom are absent; but the number of nitrogen atoms in X ¹ to X ⁵ is 1 to 3; L ¹ is a single bond or an arylene group). The light-emitting element according to claim 1, wherein the compound having an aromatic heterocyclic group containing an electron-accepting nitrogen is a compound represented by the following formula (5): (In the formula (5), R ⁵¹ to R ⁵⁷ and L ² to L ⁴ are the same as defined above; and R ⁶¹ is hydrogen, alkyl, cycloalkyl, heterocyclic, alkenyl, cycloalkenyl or alkynyl. , alkoxy, alkylthio, aryl ether, aryl sulfide, aryl, heteroaryl, halogen, carbonyl, carboxyl, oxycarbonyl, aminecardenyl, amine, or fluorenyl; L ¹ Arylene). The light-emitting element according to claim 1, wherein the compound having an aromatic heterocyclic group containing an electron-accepting nitrogen is a compound represented by the following formula (6) or (7): (In the formula (6) or (7), R ⁵¹ to R ⁵⁷ and L ¹ to L ⁴ are the same as defined above; and R ⁶¹ is hydrogen, alkyl, cycloalkyl, heterocyclic, alkenyl or cyclic. Alkenyl, alkynyl, alkoxy, alkylthio, aryl ether, aryl sulfide, aryl, heteroaryl, halogen, carbonyl, carboxyl, oxycarbonyl, aminecaraki, amine, or hydrazine base). The light-emitting element according to any one of claims 1 to 3, wherein the hole transporting layer is a compound represented by the following formula (8): (In the formula (8), R ¹ to R ³ and R ¹⁸ are the same as described above). The light-emitting element according to any one of claims 1 to 3, wherein, in the above formula (1), R ¹ and R ² are different groups. The light-emitting element of claim 4, wherein in the above formula (8), R ¹ and R ² are different groups. The light-emitting element according to any one of claims 1 to 3, wherein in the above formulas (4) to (7), the number of nitrogen atoms in X ¹ to X ⁵ is 1 to 3, And no more than two nitrogen atoms in X ¹ to X ⁵ are adjacent to each other. The light-emitting element of claim 4, wherein in the above formulas (4) to (7), the number of nitrogen atoms in X ¹ to X ⁵ is 1 to 3, and X ¹ to X ⁵ are not More than two nitrogen atoms are adjacent to each other. The light-emitting element of claim 5, wherein in the above formulas (4) to (7), the number of nitrogen atoms in X ¹ to X ⁵ is 1 to 3, and X ¹ to X ⁵ are not More than two nitrogen atoms are adjacent to each other. The light-emitting element according to any one of claims 1 to 3, wherein, in the above formulas (4) to (7), X ¹ , X ³ and X ⁵ are nitrogen atoms. The light-emitting element of claim 4, wherein in the above formulae (4) to (7), X ¹ , X ³ and X ⁵ are nitrogen atoms. The light-emitting element of claim 5, wherein in the above formulae (4) to (7), X ¹ , X ³ and X ⁵ are nitrogen atoms.