JP7037543B2 - Organic electroluminescent device - Google Patents

Description

The present invention relates to an organic electroluminescent device (referred to as an organic EL device).

By applying a voltage to the organic EL element, holes are injected into the light emitting layer from the anode and electrons are injected from the cathode into the light emitting layer. Then, in the light emitting layer, the injected holes and electrons are recombined to generate excitons. At this time, singlet excitons and triplet excitons are generated at a ratio of 1: 3 according to the statistical law of electron spin. It is said that the internal quantum efficiency of a fluorescent emission type organic EL device that uses light emission by a singlet exciton is limited to 25%. On the other hand, it is known that the phosphorescent organic EL element that uses light emission by triplet excitons can increase the internal quantum efficiency to 100% when intersystem crossing is efficiently performed from the singlet excitons. Has been done.
In recent years, technologies for extending the life of phosphorescent organic EL devices have been developed and are being applied to displays such as mobile phones. However, as for the blue organic EL element, a practical phosphorescent type organic EL element has not been developed, and there is a demand for the development of a blue organic EL element having high efficiency and long life.

More recently, a highly efficient delayed fluorescent organic EL device using delayed fluorescence has been developed. For example, Patent Document 1 discloses an organic EL device using a TTF (Triplet-Triplet Fusion) mechanism, which is one of the mechanisms of delayed fluorescence. The TTF mechanism utilizes the phenomenon that singlet excitons are generated by the collision of two triplet excitons, and it is theoretically thought that the internal quantum efficiency can be increased to 40%. However, since the efficiency is lower than that of the phosphorescent light emitting type organic EL element, further improvement in efficiency is required.

On the other hand, Patent Document 2 discloses an organic EL device using a Thermally Activated Delayed Fluorescence (TADF) mechanism. The TADF mechanism utilizes the phenomenon that reverse intersystem crossing from a triplet exciter to a singlet exciter occurs in a material with a small energy difference between the singlet level and the triplet level, and theoretically determines the internal quantum efficiency. It is believed that it can be increased to 100%. However, as with the phosphorescent light emitting device, further improvement in life characteristics is required. Such a delayed fluorescent organic EL device is characterized by high luminous efficiency, but further improvement is required.

Patent Document 2 discloses the use of an indrocarbazole compound as a TADF material.

Patent Document 3 discloses a compound obtained by deuterating an indolocarbazole compound as shown below.

Patent Document 4 discloses the use of a deuterated indrocarbazole compound as a host material.

WO2010 / 134350 Gazette WO2011 / 070963 issue WO 2011/059463 Gazette WO 2012/08795 Gazette

In order to apply an organic EL element to a display element such as a flat panel display or a light source, it is necessary to improve the luminous efficiency of the element and at the same time ensure sufficient stability during driving. In view of the above situation, it is an object of the present invention to provide a practically useful organic EL device having high efficiency and high drive stability.

INDUSTRIAL APPLICABILITY In an organic EL element including one or more light emitting layers between an opposing anode and a cathode, at least one light emitting layer thermally activates delayed fluorescence emission of a compound represented by the following general formula (1). It is an organic EL element characterized by being contained as a material.

Here, Z is a condensed aromatic heterocycle represented by the formula (2), ring A is an aromatic hydrocarbon ring represented by the formula (2a), and ring B is represented by (2b). It is a heterocycle, and ring A and ring B are fused with adjacent rings at arbitrary positions. Ar ¹ is an substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 18 carbon atoms, or the aromatic hydrocarbon group and the aromatic heterocycle. It is a linked aromatic group composed of 2 to 8 aromatic rings of an aromatic group selected from the groups. Ar ² is an substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 18 carbon atoms, or the aromatic hydrocarbon group and the aromatic complex. It is a linked aromatic group composed of 2 to 8 aromatic rings of an aromatic group selected from the ring groups. When Ar ¹ and Ar ² are linked aromatic groups, the linked aromatic rings may be the same or different, and may be linear or branched. R ¹ is independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted diarylamino group having 12 to 44 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or It is a substituted or unsubstituted aromatic heterocyclic group having 3 to 18 carbon atoms. n represents an integer of 1 to 2, a represents an integer of 0 to 4, and b represents an integer of 0 to 2. The compound represented by the general formula (1) has at least one deuterium.

As a preferred embodiment of the general formula (1), there is any of the following general formulas (3) to (8), and any of the general formulas (3) to (6) is more preferable. Further, it is preferable that L in the general formulas (3) to (8) is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms.

Here, Ar ² , a, b and R ¹ are synonymous with the general formula (1). L is a single-bonded, substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms. Ar ³ is represented by the general formula (9), X represents CR ² or N, and at least one X represents N. R ² is hydrogen, an aliphatic hydrocarbon group having 3 to 10 carbon atoms, an substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, and an substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms. , Or a linked aromatic group composed of 2 to 5 aromatic rings of an aromatic group selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. When R ² is a linked aromatic group, the linked aromatic rings may be the same or different, and may be linear or branched. a represents an integer of 0 to 4, and b represents an integer of 0 to 2. The compounds represented by the general formulas (3) to (8) have at least one deuterium.

ここで、Ar⁴はベンゼン、ジベンゾフラン、ジベンゾチオフェン、カルバゾール、カルボラン、トリアジン、又はこれらが２～３個連結した化合物から生じるｐ価の基を表す。pは１又は２の整数を表し、qは０～４の整数を表すが、Ar⁴がベンゼンから生じるｐ価の基である場合、qは１～４の整数を表す。The organic EL device of the present invention can contain a host material in a light emitting layer containing a thermally activated delayed fluorescent material represented by the general formula (1).
The host material includes a compound represented by the following general formula (10).

Here, Ar ⁴ represents a p-valent group resulting from benzene, dibenzofuran, dibenzothiophene, carbazole, carborane, triazine, or a compound in which two or three of these are linked. p represents an integer of 1 or 2 and q represents an integer of 0-4, where q represents an integer of 1-4 if Ar ⁴ is the group of p-valences derived from benzene.

The light emitting layer can contain at least two kinds of host materials represented by the general formula (10).

It is preferable that the excited triplet energy (T1) of the host material is larger than the excited singlet energy (S1) of the thermally activated delayed fluorescent material represented by the general formula (1).

The layer adjacent to the light emitting layer may contain a compound represented by the general formula (10).

The difference between the excited singlet energy (S1) and the excited triplet energy (T1) of the thermally activated delayed fluorescent material represented by the general formula (1) in the light emitting layer is preferably 0.2 eV or less.

Since the organic EL element of the present invention contains a specific thermally activated delayed fluorescent material in the light emitting layer, it is a delayed fluorescent organic EL element having high luminous efficiency and long life.

It is a schematic cross-sectional view which showed an example of an organic EL element.

The organic EL element of the present invention has one or more light emitting layers between the facing anode and the cathode, and at least one of the light emitting layers is the thermally activated delayed fluorescence represented by the above general formula (1). Contains materials (referred to as TADF materials). This organic EL device has an organic layer composed of a plurality of layers between the opposite anode and the cathode, and at least one of the plurality of layers is a light emitting layer, and the light emitting layer contains a host material as necessary. The preferred host material is the compound represented by the above general formula (10).

The above general formula (1) will be described.
Z is a condensed aromatic heterocycle represented by the formula (2), ring A in the formula (2) is an aromatic hydrocarbon ring represented by the formula (2a), and ring B is the formula (2b). It is a heterocycle represented by, and ring A and ring B are fused with adjacent rings at arbitrary positions. n represents an integer of 1 to 2, preferably an integer of 1.

The compound represented by the general formula (1) has at least one deuterium. That is, the general formula (1) is expressed by, for example, CnHmXq (where X is a heteroatom and q is an integer of 2 or more), but at least one of m H is deuterium. It is hydrogen D. Preferably, 10% or more, more preferably 20% or more of m H's are D on average.

In the general formula (1) or formula (2b), Ar ¹ is an n-valent group and Ar ² is a monovalent group.
Ar ¹ and Ar ² are independently substituted or unsubstituted aromatic hydrocarbon groups having 6 to 30 carbon atoms, substituted or unsubstituted aromatic heterocyclic groups having 3 to 18 carbon atoms, or the aromatic hydrocarbon groups. And represents a linked aromatic group composed of 2 to 8 aromatic rings of an aromatic group selected from the aromatic heterocyclic groups. Preferably, an substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or the aromatic hydrocarbon group and the aromatic heterocycle is preferable. It is a linked aromatic group composed of 2 to 8 aromatic rings of an aromatic group selected from the groups. More preferably, an substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 9 carbon atoms, or the aromatic hydrocarbon group and the aromatic complex. It represents a linked aromatic group composed of 2 to 8 aromatic rings of an aromatic group selected from the ring groups.
When Ar ¹ and Ar ² are linked aromatic groups, the linked aromatic rings may be the same or different, and may be linear or branched.

The linked aromatic group referred to in the present specification refers to a group having a structure in which two or more aromatic rings of an aromatic group selected from an aromatic hydrocarbon group and an aromatic heterocyclic group are directly bonded by a direct bond, and is a substituent. It is understood that the aromatic rings may be different or may be branched.

Specific examples of Ar ¹ and Ar ² include benzene, naphthalene, acenaften, acenaphtylene, azulene, anthracene, chrysen, pyrene, perylene, phenanthren, triphenylene, colannurene, coronen, tetracene, pentasen, fluorene, benzo [a] anthracene, and benzo. [b] Fluorene, benzo [a] pyrene, indeno [1,2,3-cd] pyrene, dibenzo [a, h] anthracene, pisen, tetraphenylene, anthracene, 1,12-benzoperylene, heptasen, hexasen, Ppyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrol, pyrazole, imidazole, triazole, thiazyl, pyrazine, furan, isoxazole, oxazole, oxadiazol, quinoline, isoquinoline, quinoxalin, quinazoline, thiazyl, benzotriazine, Phtalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole, benzothiazol, purine, pyranone, coumarin, isocmarine, chromon, dibenzofuran, dibenzothiophene, dibenzoselenophene , Carbazole or a group formed by taking hydrogen from a linked aromatic compound composed of 2 to 8 of these linked together. Here, in the case of Ar ¹ , it is a group generated by taking n hydrogens, and in the case of Ar ² , it is a group generated by taking one hydrogen.
Preferably, benzene, naphthalene, acenaften, acenaphtylene, azulene, anthracene, chrysene, pyrene, perylene, phenanthrene, triphenylene, colannurene, tetracene, fluorene, benzo [a] anthracene, benzo [b] fluorentene, benzo [a] pyrene, pyridine. , Pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrol, pyrazole, imidazole, triazole, thiazyl, pyrazine, furan, isoxazole, oxazole, oxadiazol, quinoline, isoquinoline, quinoxalin, quinazoline, thiazol, benzotriazole, phthalazine. , Tetrazole, indol, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole, benzothiazole, purine, pyranone, coumarin, isothiazole, chromon, dibenzofuran, dibenzothiophene, dibenzoselenophene, Examples thereof include carbazole, or a group formed by taking hydrogen from a linked aromatic compound composed of 2 to 8 linked carbazoles. More preferably, benzene, naphthalene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrol, pyrazole, imidazole, triazole, thiazylazole, pyrazine, furan, isoxazole, oxazole, oxadiazole, quinoline, isoquinoline, quinoxalin. , Kinazoline, thiathiazole, benzotriazole, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole, benzothiazole, purine, pyranone, coumarin, isothiazole, chromon, Alternatively, a group formed by taking hydrogen from a linked aromatic compound composed of 2 to 8 of these linked together can be mentioned.

In the general formula (1) or the formula (2) or the formula (2a), R ¹ is independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms and a substituted or unsubstituted diarylamino group having 12 to 44 carbon atoms. It represents a substituted or unsubstituted aromatic hydrocarbon group having 3 to 18 carbon atoms or an substituted or unsubstituted aromatic heterocyclic group having 3 to 18 carbon atoms. Preferably, it is an aliphatic hydrocarbon group having 1 to 8 carbon atoms, a substituted or unsubstituted diarylamino group having 12 to 22 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 3 to 12 carbon atoms, or a substituted or substituted aromatic hydrocarbon group. Represents an unsubstituted aromatic heterocyclic group having 3 to 15 carbon atoms. More preferably, it represents a substituted or unsubstituted aromatic hydrocarbon group having 3 to 10 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms.
a represents an integer of 0 to 4, preferably an integer of 0 to 2, and more preferably an integer of 0 to 1. b represents an integer of 0 to 2, preferably an integer of 0 to 1.

Specific examples of R ¹ are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, diphenylamino, naphthylphenylamino, dinaphthylamino, dianthranylamino, and diphenanthrenyl. Examples thereof include amino, phenyl, biphenylyl, turfenyl, naphthyl, pyridyl, pyrimidyl, triazil, dibenzofuranyl, dibenzothienyl, carbazolyl and the like. Preferably, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, diphenylamino, naphthylphenylamino, dinaphthylamino, phenyl, naphthyl, pyridyl, pyrimidyl, triazil, dibenzofuranyl, dibenzothienyl, or carbazolyl. And so on. More preferably, phenyl, naphthyl, pyridyl, pyrimidyl, or triadyl can be mentioned.

Preferred embodiments of the general formula (1) include general formulas (3) to (8). In the general formulas (3) to (8), Ar ² , a, b and R ¹ are synonymous with the general formula (1).
L is a single-bonded, substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms, and is preferably single-bonded, substituted or substituted. An unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, or an substituted or unsubstituted aromatic heterocyclic group having 3 to 8 carbon atoms, more preferably a single bond, substituted or unsubstituted phenyl group. Alternatively, it is a substituted or unsubstituted aromatic heterocyclic group having 3 to 6 carbon atoms.

Specific examples of the above L include benzene, naphthalene, acenaphthene, acenaphtylene, azulene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrol, pyrazole, imidazole, triazole, thiadiazole, pyrazine, and furan. , Isoxazole, oxazole, oxadiazole, quinoline, isoquinoline, quinoxalin, quinazoline, thiadiazole, benzotriazole, phthalazine, tetrazole, indol, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole. , Benzothiazole, purine, pyranone, coumarin, isothiazole, chromon, dibenzofuran, dibenzothiophene, dibenzoselenophene, carbazole and the like, except for two hydrogen groups. Preferably, a single bond or benzene, naphthalene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrol, pyrazole, imidazole, triazole, thiazole, pyrazine, furan, isoxazole, oxazole, oxadiazole, quinoline, Examples thereof include groups derived from isoquinoline, quinoxalin, quinazoline, thiathiazole, benzotriazole, phthalazine, tetrazole, indol, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole and the like. More preferably, it may be a single bond or a group derived from benzene, pyridine, pyrimidine, triazine, thiophene.

In the general formulas (3) to (8), Ar ³ is a group represented by the formula (9).
In equation (9), X represents CR ² or N and at least one X represents N. R ² is hydrogen, an aliphatic hydrocarbon group having 3 to 10 carbon atoms, an substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, and an substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms. , Or a linked aromatic group composed of 2 to 5 aromatic rings of an aromatic group selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. Preferably, hydrogen, an substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 8 carbon atoms, or the aromatic hydrocarbon group and the aromatic group is preferable. It represents a linked aromatic group composed of 2 to 5 aromatic rings of an aromatic group selected from a heterocyclic group. More preferably, hydrogen, an substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 6 carbon atoms, or the aromatic hydrocarbon group and the aromatic. It represents a linked aromatic group composed of 2 to 4 aromatic rings of an aromatic group selected from the group heterocyclic groups. The description of the linked aromatic group is the same as when Ar ¹ and Ar ² are linked aromatic groups.

In the present specification, when an aromatic hydrocarbon group, an aromatic heterocyclic group or the like has a substituent, preferred substituents are an aliphatic hydrocarbon group having 1 to 10 carbon atoms and an alkoxy group having 1 to 10 carbon atoms. , An alkylthio group having 1 to 10 carbon atoms, an alkylsilyl group having 3 to 30 carbon atoms and the like.

Specific examples of the compound represented by the general formula (1) are shown below, but the present invention is not limited to these exemplary compounds. The following compounds are compounds in which at least one hydrogen is substituted with deuterium, but the substitution position is not specified.

The method of using at least one hydrogen of the compound represented by the general formula (1) as dehydrogen is not particularly limited, but a dehydrogenated compound is used as a reaction raw material or a precursor compound, or it is represented by the general formula (1). After obtaining the non-heavy hydrogen compound, the non-heavy hydrogen compound is dehydrogenated in the presence of a Lewis acid H / D exchange catalyst (aluminum trichloride or ethyl aluminum chloride, or an acid such as CF ₃ COOD or DCl). It can be prepared by treating with a compound solvent. The degree of deuteration can be determined by NMR analysis and mass spectrometry.

By incorporating the compound represented by the general formula (1) as a TADF material in the light emitting layer, an excellent delayed fluorescent organic EL device can be obtained.

Further, the light emitting layer may contain a host material together with the TADF material, if necessary. By containing the host material, it becomes an excellent organic EL element. In this case, the TADF material is also referred to as a dopant. The host material promotes light emission from the TADF material, which is a dopant. It is desirable that the host material has an excited triplet energy (T1) greater than the excited singlet energy (S1) of the TADF material.

The compound represented by the general formula (1) preferably has a difference (ΔE) between the excited singlet energy (S1) and the excited triplet energy (T1) of 0.2 eV or less, and by showing such ΔE. It is an excellent thermally activated delayed fluorescent light emitting material.

As the host material, the compound represented by the above general formula (10) is suitable.
In the general formula (10), Ar ⁴ is a p-valent group and is produced by removing p hydrogens from benzene, dibenzofuran, dibenzothiophene, carbazole, carborane, triazine, or a linked compound in which two or three of these are linked. It is the basis. Here, the linking compound is a compound having a structure in which a ring of benzene, dibenzofuran, dibenzothiophene, carbazole, or carborane is directly linked by a direct bond, and the group generated by removing two hydrogens from these compounds is, for example,-. It is represented by Ar-Ar-, -Ar-Ar-Ar-, or -Ar-Ar (Ar)-. Here, Ar is a ring of benzene, dibenzofuran, dibenzothiophene, carbazole, or carborane, and a plurality of Ars may be the same or different. Preferred linking compounds include biphenyl or terphenyl, which is a compound in which two or three benzene rings are linked.

Preferably, Ar ⁴ is a p-valent group produced by taking p hydrogens from benzene, biphenyl, terphenyl, dibenzofuran, N-phenylcarbazole, carborane, or triazine. p represents an integer of 1 or 2, preferably an integer of 1. q represents an integer of 0 to 4, preferably an integer of 0 to 3, more preferably an integer of 0 to 2, but if Ar ⁴ is a p-valent group derived from benzene, q is 0. There is no.

The compound represented by the general formula (10) has an Ar ⁴ and a carbazole ring, and the Ar ⁴ and the carbazole ring may have a substituent as long as the function as a host is not impaired. Examples of such a substituent include a hydrocarbon group having 1 to 8 carbon atoms and an alkoxy group having 1 to 8 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms. ..

Specific examples of the compound represented by the general formula (10) are shown below.

By having a light emitting layer containing a thermally activated delayed fluorescent material selected from the compounds represented by the general formula (1), an organic EL device capable of delayed fluorescent emission can be obtained. Further, an organic EL device having a light emitting layer containing this thermally activated delayed fluorescent material as a dopant material and containing a host material selected from the compounds represented by the general formula (10), has more excellent characteristics. Can be provided. Furthermore, the characteristics can be improved by containing two or more kinds of host materials. When two kinds of hosts are contained, at least one kind may be a host material selected from the compound represented by the general formula (10). It is preferable that the first host is a compound represented by the general formula (10). The second host may be the compound of the general formula (10) or another host material, but is preferably a compound represented by the general formula (10).

Here, S1 and T1 are measured as follows.
A sample compound is deposited on a quartz substrate by a vacuum vapor deposition method under the conditions of a vacuum degree of 10 ^-4 Pa or less to form a thin-film vapor deposition film with a thickness of 100 nm. S1 measures the emission spectrum of this vapor deposition film, draws a tangent to the rising edge of the emission spectrum on the short wavelength side, and formulates the wavelength value λedge [nm] at the intersection of the tangent and the horizontal axis by the following equation ( Substitute in i) to calculate S1.
S1 [eV] = 1239.85 / λedge (i)

T1 measures the phosphorescence spectrum of the above-mentioned vapor deposition film, draws a tangent to the rising edge of the phosphorescence spectrum on the short wavelength side, and sets the wavelength value λedge [nm] at the intersection of the tangent and the horizontal axis in equation (ii). Substitute in to calculate T1.
T1 [eV] = 1239.85 / λedge (ii)

Next, the structure of the organic EL element of the present invention will be described with reference to the drawings, but the structure of the organic EL element of the present invention is not limited to this.

FIG. 1 is a cross-sectional view showing a structural example of a general organic EL device used in the present invention, in which 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, and 5 is a light emitting layer. , 6 represent an electron transport layer, and 7 represents a cathode. The organic EL device of the present invention may have an exciton blocking layer adjacent to the light emitting layer, or may have an electron blocking layer between the light emitting layer and the hole injection layer. The exciton blocking layer can be inserted into either the cathode side or the cathode side of the light emitting layer, and both can be inserted at the same time. The organic EL device of the present invention has an anode, a light emitting layer, and a cathode as essential layers, but it is preferable to have a hole injection transport layer and an electron injection transport layer in addition to the essential layers, and further, a light emitting layer and an electron injection. It is preferable to have a hole blocking layer between the transport layers. The hole injection transport layer means either or both of the hole injection layer and the hole transport layer, and the electron injection transport layer means either or both of the electron injection layer and the electron transport layer.

It is also possible to stack the cathode 7, the electron transport layer 6, the light emitting layer 5, the hole transport layer 4, and the anode 2 in this order on the substrate 1, which is the opposite structure to that of FIG. It can be added or omitted.

-substrate-
The organic EL element of the present invention is preferably supported by a substrate. The substrate is not particularly limited as long as it is conventionally used for an organic EL element, and for example, a substrate made of glass, transparent plastic, quartz or the like can be used.

-anode-
As the anode material in the organic EL element, a material having a large work function (4 eV or more), an alloy, an electrically conductive compound, or a mixture thereof is preferably used. Specific examples of such electrode materials include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. Further, an amorphous material such as IDIXO (In ₂ O ₃ -ZnO) capable of producing a transparent conductive film may be used. For the anode, a thin film may be formed by forming a thin film of these electrode materials by a method such as thin film deposition or sputtering, and a pattern of a desired shape may be formed by a photolithography method, or when pattern accuracy is not required so much (about 100 μm or more). May form a pattern through a mask having a desired shape during vapor deposition or sputtering of the electrode material. Alternatively, when a coatable substance such as an organic conductive compound is used, a wet film forming method such as a printing method or a coating method can also be used. When light emission is taken out from this anode, it is desirable to increase the transmittance to more than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. The film thickness depends on the material, but is usually selected in the range of 10 to 1000 nm, preferably 10 to 200 nm.

-cathode-
On the other hand, as the cathode material, a material consisting of a metal having a small work function (4 eV or less) (referred to as an electron-injectable metal), an alloy, an electrically conductive compound, or a mixture thereof is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O). ₃ ) Examples include mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among these, from the viewpoint of electron injectability and durability against oxidation, etc., a mixture of an electron injectable metal and a second metal, which is a stable metal having a larger work function value than this, for example, a magnesium / silver mixture, magnesium. / Aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, lithium / aluminum mixture, aluminum and the like are suitable. The cathode can be produced by forming a thin film of these cathode materials by a method such as vapor deposition or sputtering. The sheet resistance of the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm. In order to transmit the emitted light, if either the anode or the cathode of the organic EL element is transparent or translucent, the emission brightness is improved, which is convenient.

Further, by forming the above metal on the cathode with a thickness of 1 to 20 nm and then forming the conductive transparent material mentioned in the description of the anode on the cathode, a transparent or translucent cathode can be produced. By applying this, it is possible to manufacture an element in which both the anode and the cathode have transparency.

-Light emitting layer-
The light emitting layer is a layer that emits light after excitons are generated by recombination of holes and electrons injected from the anode and the cathode, respectively. The TADF material of the present invention may be used alone or the TADF material of the present invention may be used together with the host material for the light emitting layer. When used with host materials, the TADF materials of the invention are organic light emitting dopant materials.

As the organic light emitting dopant material, only one kind may be contained in the light emitting layer, or two or more kinds may be contained. The content of the TADF material or the organic light emitting dopant material is preferably 0.1 to 50 wt%, more preferably 1 to 30 wt% with respect to the host material.
Since the organic EL element of the present invention utilizes delayed fluorescent emission, a dopant such as the Ir complex used in a phosphorescent organic EL element is not used.

As the host material in the light emitting layer, a known host material used in a phosphorescent light emitting device or a fluorescent light emitting device can be used, but it is preferable to use the compound represented by the general formula (10). Further, a plurality of types of host materials may be used in combination. When a plurality of types of host materials are used in combination, it is preferable that at least one type of host material is selected from the compounds represented by the general formula (10).

Known host materials that can be used are compounds that have hole-transporting ability, electron-transporting ability, and high glass transition temperature, and have S1 that is larger than T1 of TADF material or luminescent dopant material. Is preferable.

Since such other host materials are known from a large number of patent documents and the like, they can be selected from them. Specific examples of the host material are not particularly limited, but are indol derivatives, carbazole derivatives, indolocarbazole derivatives, triazole derivatives, oxazole derivatives, oxadiazol derivatives, imidazole derivatives, phenylenediamine derivatives, arylamine derivatives, and the like. Various metal complexes typified by styrylanthracene derivatives, fluorenone derivatives, stilben derivatives, triphenylene derivatives, carborane compounds, porphyrin compounds, phthalocyanine derivatives, metal complexes of 8-quinolinol derivatives and metal phthalocyanine, benzoxazole and benzothiazole derivatives. , Poly (N-vinylcarbazole) derivative, aniline-based copolymer, thiophene oligomer, polythiophene derivative, polyphenylene derivative, polyphenylene vinylene derivative, polyfluorene derivative and the like.

When using multiple types of host materials, each host can be vapor-deposited from different vapor deposition sources, or multiple types of hosts can be vapor-deposited simultaneously from one vapor deposition source by premixing them before vapor deposition to form a premixture. can.

-Injection layer-
The injection layer is a layer provided between the electrode and the organic layer in order to reduce the driving voltage and improve the emission brightness. The injection layer includes a hole injection layer and an electron injection layer, and is located between the anode and the light emitting layer or the hole transport layer. And may be present between the cathode and the light emitting layer or the electron transporting layer. The injection layer can be provided as needed.

-Hole blocking layer-
The hole blocking layer has the function of an electron transporting layer in a broad sense, and is made of a hole blocking material having a function of transporting electrons and a significantly small ability to transport holes. It is possible to improve the recombination probability of electrons and holes in the light emitting layer by blocking the above.
A known hole blocking material can be used for the hole blocking layer, but it is preferable to use the compound represented by the general formula (10). Further, a plurality of types of hole blocking materials may be used in combination.

-Electronic blocking layer-
The electron blocking layer has a function of a hole transporting layer in a broad sense, and by blocking electrons while transporting holes, the probability of recombination of electrons and holes in the light emitting layer can be improved. ..
As the material of the electron blocking layer, a known electron blocking layer material can be used, but it is preferable to use the compound represented by the general formula (10). The film thickness of the electron blocking layer is preferably 3 to 100 nm, more preferably 5 to 30 nm.

-Exciton blocking layer-
The exciton blocking layer is a layer for blocking excitons generated by recombination of holes and electrons in the light emitting layer from diffusing into the charge transport layer, and excitons are inserted by inserting this layer. It is possible to efficiently confine it in the light emitting layer, and it is possible to improve the light emitting efficiency of the element. The exciton blocking layer can be inserted between two adjacent light emitting layers in an element in which two or more light emitting layers are adjacent to each other.
As the material of the exciton blocking layer, a known exciton blocking layer material can be used, but it is preferable to use the compound represented by the general formula (10).

The layers adjacent to the light emitting layer include a hole blocking layer, an electron blocking layer, an exciton blocking layer, and the like, but if these layers are not provided, the hole transport layer, the electron transport layer, and the like are adjacent layers. Become. It is preferable to use a compound represented by the general formula (10) for at least one of the two adjacent layers.

-Hole transport layer-
The hole transport layer is made of a hole transport material having a function of transporting holes, and the hole transport layer may be provided with a single layer or a plurality of layers.

The hole transporting material has any of hole injection, transport, and electron barrier properties, and may be either an organic substance or an inorganic substance. Any compound can be selected and used for the hole transport layer from conventionally known compounds. Examples of such hole transport materials include porphyrin derivatives, arylamine derivatives, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, and amino-substituted carcon derivatives. , Oxazole derivative, styrylanthracene derivative, fluorenone derivative, hydrazone derivative, stilben derivative, silazane derivative, aniline-based copolymer, and conductive polymer oligomer, especially thiophene oligomer. It is preferable to use an amine derivative, and it is more preferable to use an arylamine compound.

-Electron transport layer-
The electron transport layer is made of a material having a function of transporting electrons, and the electron transport layer may be provided with a single layer or a plurality of layers.

The electron transporting material (which may also serve as a hole blocking material) may have a function of transmitting electrons injected from the cathode to the light emitting layer. For the electron transport layer, any conventionally known compound can be selected and used, for example, a polycyclic aromatic derivative such as naphthalene, anthracene, phenanthroline, tris (8-quinolinolate) aluminum (III). Derivatives, phosphine oxide derivatives, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyrandioxide derivatives, carbodiimide, fleolenilidene methane derivatives, anthracinodimethane and antron derivatives, bipyridine derivatives, quinoline derivatives, oxadiazole derivatives, benzoimidazole Derivatives, benzothiazole derivatives, indrocarbazole derivatives and the like can be mentioned. Further, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

When the organic EL device of the present invention is manufactured, the film forming method for each layer is not particularly limited, and it may be manufactured by either a dry process or a wet process.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

The compounds used in Examples and Comparative Examples are shown below.

Synthesis example 1
Synthesis of deuterated compound (104D) of compound 104

Compound 104 (2.0 g, 3.1 mmol) was placed in a 100 mL three-necked flask, 25 g of heavy benzene was added, and the mixture was stirred at room temperature under a nitrogen atmosphere. Deuterated trifluic acid (12.0 g, 104 mmol) was added, and the mixture was stirred at 50 ° C. for 5 hours. A heavy aqueous solution of sodium carbonate was added, and the organic layer was washed with water. Magnesium sulfate was added to the organic layer, dried and filtered, and then concentrated and dried. Further, the solid obtained by recrystallization was purified by sublimation to obtain 1.6 g of a deuterated compound (104D) of compound 104.
The deuteration rate of compound 104D calculated from the results of mass spectrometry was about 31%.
APCI-TOFMS m / z: 650 [M + 1] ⁺

Synthesis Examples 2 to 8
By deuterating compounds 115, 119, 125, 131, 142, 150, or 158 in the same manner as in Synthesis Example 1, the respective deuterated compounds 115D, 119D, 125D, 131D, 142D, 150D , Or 158D, respectively.

The S1 and T1 of the deuterated product and the compound 104 before deuteration were measured. Furthermore, S1 and T1 of the compounds 215, 217, 238, 243, and mCP were measured. The measurement method and the calculation method are the same as those described above.

Experimental Example 1
The fluorescence lifetime of compound 104D was measured. Compound 104D and compound 217 are vapor-deposited from different vapor deposition sources on a quartz substrate under the conditions of a vacuum degree of ^10-4 Pa or less, and a co-deposited film having a concentration of compound 104D of 15% by weight is formed at 100 nm. Formed by thickness. The emission spectrum of this thin film was measured, and emission with a peak of 483 nm was confirmed. In addition, the emission lifetime was measured with a small fluorescence lifetime measuring device (Quantaurus-tau manufactured by Hamamatsu Photonics Co., Ltd.) in a nitrogen atmosphere. Fluorescence with an excitation lifetime of 12 ns and delayed fluorescence of 13 μs were observed, confirming that compound 104D is a compound showing delayed fluorescence emission.

When the fluorescence lifetime of the deuterated substances 115D, 119D, 125D, 131D, 142D, 150D, and 158D was measured in the same manner as above, delayed fluorescence was observed and it was confirmed that the material exhibits delayed fluorescence emission. .. In addition, for compounds 104, 115, 119, 125, 131, 142, 150, and 158 before deuteration, delayed fluorescence was observed when the fluorescence lifetime was measured in the same manner, and the material showed delayed fluorescence emission. It was confirmed that there was.

Example 1
Each thin film was laminated with a vacuum degree of 4.0 × 10 ^-5 Pa by a vacuum vapor deposition method on a glass substrate on which an anode made of ITO having a film thickness of 70 nm was formed. First, HAT-CN was formed on the ITO to a thickness of 10 nm as a hole injection layer, and then HT-1 was formed to a thickness of 25 nm as a hole transport layer. Next, compound (217) was formed to a thickness of 5 nm as an electron blocking layer. Then, the compound (217) as a host and the compound (104D) as a dopant were co-deposited from different vapor deposition sources to form a light emitting layer having a thickness of 30 nm. At this time, co-deposited under the vapor deposition conditions where the concentration of the compound (104D) was 15 wt%. Next, compound (238) was formed to a thickness of 5 nm as a hole blocking layer. Next, ET-1 was formed to a thickness of 40 nm as an electron transport layer. Further, lithium fluoride (LiF) was formed on the electron transport layer as an electron injection layer to a thickness of 1 nm. Finally, aluminum (Al) was formed as a cathode on the electron injection layer to a thickness of 70 nm to fabricate an organic EL device.

Examples 2 to 11 and Comparative Examples 1 to 8
An organic EL device was produced in the same manner as in Example 1 except that the dopant and the host were the compounds shown in Table 2.

Examples 12, 13
An organic EL device was produced in the same manner as in Example 1 except that the electron blocking layer, the host, and the hole blocking layer were the compounds shown in Table 2.

Example 14
Each thin film was laminated with a vacuum degree of 4.0 × 10 ^-5 Pa by a vacuum vapor deposition method on a glass substrate on which an anode made of ITO having a film thickness of 70 nm was formed. First, HAT-CN was formed on the ITO to a thickness of 10 nm as a hole injection layer, and then HT-1 was formed to a thickness of 25 nm as a hole transport layer. Next, compound (217) was formed to a thickness of 5 nm as an electron blocking layer. Next, compound (217) as a host, compound (238) as a second host, and compound (104D) as a dopant were co-deposited from different vapor deposition sources to form a light emitting layer to a thickness of 30 nm. At this time, co-deposited under the vapor deposition conditions where the concentration of the compound (104D) was 15 wt% and the weight ratio between the host and the second host was 50:50. Next, compound (238) was formed to a thickness of 5 nm as a hole blocking layer. Next, ET-1 was formed to a thickness of 40 nm as an electron transport layer. Further, lithium fluoride (LiF) was formed on the electron transport layer as an electron injection layer to a thickness of 1 nm. Finally, aluminum (Al) was formed as a cathode on the electron injection layer to a thickness of 70 nm to fabricate an organic EL device.

Table 2 shows the compounds used as the dopant, the host, the second host, the hole blocking layer, and the electron blocking layer.

Table 3 shows the maximum emission wavelength, external quantum efficiency, and lifetime of the emission spectrum of the manufactured organic EL device. The maximum emission wavelength and external quantum efficiency are the values when the drive current density is 2.5 mA / cm ² , which are the initial characteristics. The life was measured by measuring the time until the brightness attenuated to 95% of the initial brightness at an initial brightness of 500 cd / m ² .

The organic EL element using the deuterated TADF material represented by the general formula (1) from Table 3 as a light emitting dopant is superior to the case where the non-deuterated TADF material is used as a light emitting dopant. It can be seen that it has a long life characteristic. It is considered that this is because the carbon-hydrogen bond became a carbon-hydrogen bond due to dehydrogenation, which increased the bond dissociation energy and suppressed the deterioration of the TADF material due to the cleavage of the carbon-hydrogen bond. Be done.

The organic EL element of the present invention is a delayed fluorescent organic EL element having high luminous efficiency and long life, and is practically useful as a display element such as a display such as a mobile phone or a light source element.

1 substrate, 2 anode, 3 hole injection layer, 4 hole transport layer, 5 light emitting layer, 6 electron transport layer, 7 cathode

Claims (9)

In an organic electroluminescent device that includes one or more light emitting layers between the opposing anode and cathode, at least one light emitting layer, together with the host material, thermally activates delayed fluorescence of the compound represented by the following general formula (1). An organic electroluminescent device characterized by being contained as a light emitting dopant material.

Here, Z is a condensed aromatic heterocycle represented by the formula (2), ring A is an aromatic hydrocarbon ring represented by the formula (2a), and ring B is represented by the formula (2b). It is a heterocyclic ring, and ring A and ring B are fused with adjacent rings at arbitrary positions.
Ar ¹ is an substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 18 carbon atoms, or the aromatic hydrocarbon group and the aromatic heterocycle. A linked aromatic group composed of 2 to 8 aromatic rings of an aromatic group selected from the groups, Ar ² is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms. It is composed of substituted or unsubstituted aromatic heterocyclic groups having 3 to 18 carbon atoms, or 2 to 8 aromatic rings of the aromatic hydrocarbon group and an aromatic group selected from the aromatic heterocyclic groups. It is a linked aromatic group. When Ar ¹ and Ar ² are linked aromatic groups, the linked aromatic rings may be the same or different, and may be linear or branched.
R ¹ is independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted diarylamino group having 12 to 44 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 3 to 18 carbon atoms, respectively. Alternatively, it is a substituted or unsubstituted aromatic heterocyclic group having 3 to 18 carbon atoms.
n represents an integer of 1 to 2, a represents an integer of 0 to 4, and b represents an integer of 0 to 2. The compound represented by the general formula (1) has at least one deuterium. The organic electroluminescent device according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by any of the following general formulas (3) to (8).

Here, Ar ² , R ¹ , a and b are synonymous with the general formula (1).
L is a single-bonded, substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms.
Ar ³ is a group represented by the formula (9), where X represents CR ² or N and at least one X represents N.
R ² is hydrogen, an aliphatic hydrocarbon group having 3 to 10 carbon atoms, an substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, and an substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms. , Or a linked aromatic group composed of 2 to 5 aromatic rings of an aromatic group selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. When R ² is a linked aromatic group, the linked aromatic rings may be the same or different, and may be linear or branched.
The compounds represented by the general formulas (3) to (8) have at least one deuterium. The organic electroluminescent device according to claim 2, wherein the compound is represented by any of the general formulas (3) to (6). The organic electric field light emitting element according to claim 2 or 3, wherein L is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms. The organic electroluminescent device according to claim 1 , wherein the host material is a compound represented by the following general formula (10).

Here, Ar ⁴ represents a p-valent group resulting from benzene, dibenzofuran, dibenzothiophene, carbazole, carborane, triazine, or a compound in which two or three of these are linked.
p represents an integer of 1 or 2 and q represents an integer of 0-4, where q is an integer of 1-4 if Ar ⁴ is the group of p-valences derived from benzene. The organic electroluminescent device according to claim 5 , further comprising at least two types of host materials represented by the general formula (10). The organic according to claim 1 , wherein the excited triplet energy (T1) of the host material is larger than the excited singlet energy (S1) of the thermally activated delayed fluorescent material represented by the general formula (1). Electroluminescent element. The organic electroluminescent device according to claim 1, wherein the layer adjacent to the light emitting layer contains a compound represented by the general formula (10). The organic electroluminescent device according to claim 1, wherein the difference between the excited singlet energy (S1) and the excited triplet energy (T1) of the compound represented by the general formula (1) is 0.2 eV or less. ..

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