WO2018173598A1

WO2018173598A1 - Organic electroluminescent element

Info

Publication number: WO2018173598A1
Application number: PCT/JP2018/006065
Authority: WO
Inventors: 匡志多田; 雄太相良
Original assignee: 新日鉄住金化学株式会社
Priority date: 2017-03-22
Filing date: 2018-02-20
Publication date: 2018-09-27
Also published as: JPWO2018173598A1; TW201843155A; JP7037543B2

Abstract

Provided is a thermally activated delayed fluorescence-type organic EL element having high luminous efficiency and a long service life. An organic EL element having light-emitting layers arranged between an anode and a cathode which face each other, wherein at least one of the light-emitting layers contains a indolocarbazole compound that serves as a thermally activated delayed fluorescence material or both of the indolocarbazole compound and a host material, the indolocarbazole compound is represented by general formula (1), Z in the formula represents an indolocarbazole ring represented by formula (2), and at least one of hydrogen atoms in the indolocarbazole compound is substituted by a deuterium atom.

Description

Organic electroluminescence device

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 from the anode and electrons from the cathode are injected into the light emitting layer. 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 rule of electron spin. A fluorescence emission type organic EL device using light emission by singlet excitons is said to have a limit of 25% in internal quantum efficiency. On the other hand, phosphorescent organic EL devices that use triplet exciton emission are known to increase internal quantum efficiency to 100% when intersystem crossing is efficiently performed from singlet excitons. It has been.
In recent years, techniques for extending the lifetime of phosphorescent organic EL elements have been developed and are being applied to displays such as mobile phones. However, regarding the blue organic EL element, a practical phosphorescent organic EL element has not been developed, and development of a blue organic EL element having high efficiency and a long life is required.

More recently, high-efficiency delayed fluorescence organic EL elements using delayed fluorescence have been developed. For example, Patent Document 1 discloses an organic EL element using a TTF (Triplet-Triplet Fusion) mechanism, which is one of delayed fluorescence mechanisms. The TTF mechanism uses 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 a phosphorescent 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 triplet excitons to singlet excitons occurs in materials where the energy difference between singlet and triplet levels is small. It is thought to be increased to 100%. However, there is a demand for further improvement in the life characteristics as in the phosphorescent light emitting device. Such a delayed fluorescence type organic EL device is characterized by high luminous efficiency, but further improvement is required.

Patent Document 2 discloses the use of an indolocarbazole 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 indolocarbazole compound as a host material.

WO2010 / 134350 Publication WO2011 / 070963 Publication WO2011 / 059463 Publication WO2012 / 087955 Publication

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 light emission efficiency of the element and at the same time to ensure sufficient stability during driving. An object of the present invention is to provide a practically useful organic EL device having high efficiency and high driving stability in view of the above-described present situation.

The present invention relates to an organic EL device comprising one or more light emitting layers between an anode and a cathode facing each other, wherein at least one light emitting layer comprises a compound represented by the following general formula (1) by thermally activated delayed fluorescence. It is an organic EL element characterized by containing as a material.

Here, Z is a condensed aromatic heterocycle represented by formula (2), ring A is an aromatic hydrocarbon ring represented by formula (2a), and ring B is represented by (2b). It is a heterocyclic ring, and ring A and ring B are each fused with an adjacent ring at an arbitrary position. Ar ¹ represents a 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 heterocyclic ring. A linked aromatic group constituted by connecting 2 to 8 aromatic rings of an aromatic group selected from a group. Ar ² represents a 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 heterocyclic group. A linked aromatic group constituted by connecting 2 to 8 aromatic rings of an aromatic group selected from cyclic groups. When Ar ¹ and Ar ² are linked aromatic groups, the aromatic rings to be linked 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 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, L in the general formulas (3) to (8) is preferably a substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms.

Here, Ar ² , a, b and R ¹ have the same meaning as in the general formula (1). L is a single bond, a 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, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms. Or a linked aromatic group constituted by connecting 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.

The organic EL device of the present invention can contain a host material in the light emitting layer containing the thermally activated delayed fluorescent material represented by the general formula (1).
Examples of the host material include a compound represented by the following general formula (10).

Here, Ar ⁴ represents a p-valent group generated from benzene, dibenzofuran, dibenzothiophene, carbazole, carborane, triazine, or a compound in which two to three of these are connected. p represents an integer of 1 or 2, and q represents an integer of 0 to 4. When Ar ⁴ is a p-valent group derived from benzene, q represents an integer of 1 to 4.

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

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

The layer represented by the general formula (10) may be contained in a layer adjacent to the light emitting layer.

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 device of the present invention contains a specific thermally activated delayed fluorescent material in the light emitting layer, it becomes a delayed fluorescent organic EL device with high luminous efficiency and long life.

It is the schematic cross section which showed an example of the organic EL element.

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

The general formula (1) will be described.
Z is a condensed aromatic heterocycle represented by formula (2), ring A in formula (2) is an aromatic hydrocarbon ring represented by formula (2a), and ring B is represented by formula (2b) Wherein ring A and ring B are each fused with an adjacent ring at an arbitrary position. 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 represented 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 heavy. Hydrogen D. Preferably, 10% or more, more preferably 20% or more of the m pieces of H on average are D.

In 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 each independently a 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 a linked aromatic group constituted by connecting 2 to 8 aromatic rings of an aromatic group selected from the aromatic heterocyclic group. Preferably, it is a 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 heterocyclic ring. A linked aromatic group constituted by connecting 2 to 8 aromatic rings of an aromatic group selected from a group. More preferably, it is a 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 heterocyclic group. A linked aromatic group constituted by connecting 2 to 8 aromatic rings of an aromatic group selected from cyclic 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 as used herein 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 bonded by a direct bond. It is understood that the aromatic rings may be different and may be branched.

Specific examples of Ar ¹ and Ar ² include benzene, naphthalene, acenaphthene, acenaphthylene, azulene, anthracene, chrysene, pyrene, perylene, phenanthrene, triphenylene, corannulene, coronene, tetracene, pentacene, fluorene, benzo [a] anthracene, benzo [b] fluoranthene, benzo [a] pyrene, indeno [1,2,3-cd] pyrene, dibenzo [a, h] anthracene, picene, tetraphenylene, anthanthrene, 1,12-benzoperylene, heptacene, hexacene, Pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, oxazole, oxadiazole, quinoline, isoquinoline, quino Sarin, quinazoline, thiadiazole, benzotriazine, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole, benzothiadiazole, purine, pyranone, coumarin, isocoumarin, chromone , Dibenzofuran, dibenzothiophene, dibenzoselenophene, carbazole, or a group formed by removing hydrogen from a linked aromatic compound formed by linking two to eight of these. Here, Ar ¹ is a group generated by taking n hydrogen atoms, and Ar ² is a group generated by taking one hydrogen gas.
Preferably, benzene, naphthalene, acenaphthene, acenaphthylene, azulene, anthracene, chrysene, pyrene, perylene, phenanthrene, triphenylene, corannulene, tetracene, fluorene, benzo [a] anthracene, benzo [b] fluoranthene, benzo [a] pyrene, pyridine , Pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, oxazole, oxadiazole, quinoline, isoquinoline, quinoxaline, quinazoline, thiadiazole, benzotriazine, phthalazine , Tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indah Benzimidazole, benzotriazole, benzoisothiazole, benzothiadiazole, purine, pyranone, coumarin, isocoumarin, chromone, dibenzofuran, dibenzothiophene, dibenzoselenophene, carbazole, or a combination of 2 to 8 of these And a group formed by removing hydrogen from a linked aromatic compound. More preferably, benzene, naphthalene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, oxazole, oxadiazole, quinoline, isoquinoline, quinoxaline , Quinazoline, thiadiazole, benzotriazine, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole, benzothiadiazole, purine, pyranone, coumarin, isocoumarin, chromone, Alternatively, hydrogen is taken from a linked aromatic compound composed of 2 to 8 of these linked together. Include groups occur.

In the general formula (1), the formula (2) or the formula (2a), each 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, It represents a substituted or unsubstituted aromatic hydrocarbon group having 3 to 18 carbon atoms, or a 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 unsubstituted It 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, 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 include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, diphenylamino, naphthylphenylamino, dinaphthylamino, dianthranylamino, diphenanthrenyl. Amino, phenyl, biphenylyl, terphenylyl, naphthyl, pyridyl, pyrimidyl, triazyl, dibenzofuranyl, dibenzothienyl, carbazolyl and the like can be mentioned. Preferably, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, diphenylamino, naphthylphenylamino, dinaphthylamino, phenyl, naphthyl, pyridyl, pyrimidyl, triazyl, dibenzofuranyl, dibenzothienyl, or carbazolyl Etc. More preferred is phenyl, naphthyl, pyridyl, pyrimidyl, or triazyl.

As preferred embodiments of the general formula (1), there are general formulas (3) to (8). In the general formulas (3) to (8), Ar ² , a, b and R ¹ have the same meaning as in the general formula (1).
L is a single bond, a 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, preferably a single bond, substituted or unsubstituted An unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 8 carbon atoms, more preferably a single bond, a substituted or unsubstituted phenyl group, Or a substituted or unsubstituted aromatic heterocyclic group having 3 to 6 carbon atoms.

Specific examples of L include a single bond, benzene, naphthalene, acenaphthene, acenaphthylene, azulene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan , Isoxazole, oxazole, oxadiazole, quinoline, isoquinoline, quinoxaline, quinazoline, thiadiazole, benzotriazine, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole , Benzothiadiazole, purine, pyranone, coumarin, isocoumarin, chromone, dibenzo Examples thereof include groups formed by removing two hydrogens from furan, dibenzothiophene, dibenzoselenophene, carbazole and the like. Preferably, a single bond or benzene, naphthalene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, oxazole, oxadiazole, quinoline, Examples include groups derived from isoquinoline, quinoxaline, quinazoline, thiadiazole, benzotriazine, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole and the like. More preferably, a group formed from a single bond or benzene, pyridine, pyrimidine, triazine, or thiophene is mentioned.

In the general formulas (3) to (8), Ar ³ is a group represented by the formula (9).
In the 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, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms. Or a connected aromatic group constituted by connecting 2 to 5 aromatic rings of an aromatic group selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. Preferably, hydrogen, a 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 It represents a linked aromatic group constituted by connecting 2 to 5 aromatic rings of an aromatic group selected from a heterocyclic group. More preferably, hydrogen, a 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 Represents a linked aromatic group constituted by connecting 2 to 4 aromatic rings of an aromatic group selected from the group A heterocyclic groups. The explanation of the linked aromatic group is the same as the case where 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 include an aliphatic hydrocarbon group having 1 to 10 carbon atoms and an alkoxy group having 1 to 10 carbon atoms. And an alkylthio group having 1 to 10 carbon atoms and an alkylsilyl group having 3 to 30 carbon atoms.

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

A method for converting at least one hydrogen of the compound represented by the general formula (1) into deuterium is not particularly limited, but a deuterated compound is used as a reaction raw material or a precursor compound, or represented by the general formula (1). And then dehydrogenating the non-deuterium compound in the presence of a Lewis acid H / D exchange catalyst (aluminum trichloride or ethylaluminum chloride, or an acid such as CF ₃ COOD or DCl). It can be prepared by treating with a solvating solvent. The degree of deuteration can be determined by NMR analysis and mass spectrometry.

An excellent delayed fluorescence organic EL device can be obtained by incorporating the compound represented by the general formula (1) into the light emitting layer as a TADF material.

In addition, the light emitting layer can contain a host material together with the TADF material, if necessary. By containing a host material, an excellent organic EL device is obtained. In this case, the TADF material is also called a dopant. The host material promotes light emission from the TADF material, which is a dopant. The host material desirably has an excited triplet energy (T1) greater than the excited singlet energy (S1) of the TADF material.

In the compound represented by the general formula (1), it is preferable that the difference (ΔE) between the excited singlet energy (S1) and the excited triplet energy (T1) is 0.2 eV or less. It becomes an excellent heat-activated delayed fluorescent material.

As the host material, a compound represented by the general formula (10) is suitable.
In the general formula (10), Ar ⁴ is a p-valent group, and is generated by removing p hydrogen from benzene, dibenzofuran, dibenzothiophene, carbazole, carborane, triazine, or a linking compound in which 2 to 3 of these are connected. It is a group. Here, the connecting compound is a compound having a structure in which rings of benzene, dibenzofuran, dibenzothiophene, carbazole, or carborane are connected by a direct bond, and a 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 examples of the linking compound 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 formed 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, and q is 0 when Ar ⁴ is a p-valent group derived from benzene. There is no.

The compound represented by the general formula (10) has Ar ⁴ and a carbazole ring. The Ar ⁴ and carbazole ring may have a substituent as long as the function as a host is not inhibited. 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 compound represented by the general formula (1), an organic EL device capable of delayed fluorescent emission can be obtained. An organic EL device having a more excellent characteristic by including a light-emitting layer containing the thermally activated delayed fluorescent material as a dopant material and containing a host material selected from the compound represented by the general formula (10) Can be provided. Further, 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 compounds represented by the general formula (10). The first host is preferably a compound represented by the general formula (10). The second host may be a 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 deposition method under a vacuum degree of 10 ⁻⁴ Pa or less to form a deposited film with a thickness of 100 nm. S1 measures the emission spectrum of this deposited film, draws a tangent to the short wavelength side rise of this emission spectrum, the wavelength value λ edge [nm] of the intersection of the tangent and the horizontal axis, Substitute into i) to calculate S1.
S1 [eV] = 1239.85 / λedge (i)

T1 measures the phosphorescence spectrum of the above deposited film, draws a tangent line to the short wavelength rise of this phosphorescence spectrum, and calculates the wavelength value λ edge [nm] of the intersection of the tangent line and the horizontal axis in the formula (ii) Substituting into 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, wherein 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 represents 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 on either the cathode side or the cathode side of the light emitting layer, or both can be inserted simultaneously. The organic EL device of the present invention has an anode, a light emitting layer, and a cathode as essential layers, but preferably has a hole injecting and transporting layer and an electron injecting and transporting layer in addition to the essential layers, and further has a light emitting layer and an electron injecting layer. 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.

The structure opposite to that shown in FIG. 1, that is, the cathode 7, the electron transport layer 6, the light emitting layer 5, the hole transport layer 4 and the anode 2 can be laminated in this order on the substrate 1. Addition and omission are possible.

-substrate-
The organic EL element of the present invention is preferably supported on a substrate. The substrate is not particularly limited, and any substrate that has been conventionally used for an organic EL element can be used. For example, a substrate made of glass, transparent plastic, quartz, or the like can be used.

-anode-
As an anode material in the organic EL element, a material made of a metal, an alloy, an electrically conductive compound or a mixture thereof having a high work function (4 eV or more) 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. Alternatively, an amorphous material such as IDIXO (In ₂ O ₃ —ZnO) that can form a transparent conductive film may be used. For the anode, these electrode materials may be formed into a thin film by a method such as vapor deposition or sputtering, and a pattern having a desired shape may be formed by a photolithography method, or the pattern accuracy is not required (about 100 μm or more). May form a pattern through a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material. Or when using the substance which can be apply | coated like an organic electroconductivity compound, wet film-forming methods, such as a printing system and a coating system, can also be used. When light emission is extracted from the anode, it is desirable that the transmittance be greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Although the film thickness depends on the material, it 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 made of a metal having a small work function (4 eV or less) (referred to as an electron injecting 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 ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among these, a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function value than this, such as a magnesium / silver mixture, magnesium, from the viewpoint of electron injectability and durability against oxidation, etc. / Aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al ₂ O ₃ ) mixtures, lithium / aluminum mixtures, aluminum and the like are preferred. 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 one of the anode or the cathode of the organic EL element is transparent or translucent, the light emission luminance is improved, which is convenient.

Further, after forming the metal with a thickness of 1 to 20 nm on the cathode, a transparent or translucent cathode can be produced by forming the conductive transparent material mentioned in the description of the anode on the cathode. By applying this, an element in which both the anode and the cathode are transmissive can be manufactured.

―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. In the light emitting layer, the TADF material of the present invention may be used alone, or the TADF material of the present invention may be used together with a host material. When used with a host material, the TADF material of the present invention is an organic light emitting dopant material.

Only one kind of organic light emitting dopant material 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 device of the present invention utilizes delayed fluorescence, a dopant such as an Ir complex used in a phosphorescent organic EL device is not used.

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

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

Such other host materials are known from a large number of patent documents, and can be selected from them. Specific examples of the host material are not particularly limited, but include indole derivatives, carbazole derivatives, indolocarbazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, phenylenediamine derivatives, arylamine derivatives, Various metal complexes represented by metal complexes of styryl anthracene derivatives, fluorenone derivatives, stilbene derivatives, triphenylene derivatives, carborane compounds, porphyrin compounds, phthalocyanine derivatives, 8-quinolinol derivatives and metal complexes of metal phthalocyanines, benzoxazole and benzothiazole derivatives , Poly (N-vinylcarbazole) derivatives, aniline copolymers, thiophene oligomers, polythiophene derivatives, polyphenylene derivatives, poly Enirenbiniren derivatives, polymer compounds such as polyfluorene derivatives, and the like.

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

-Injection layer-
The injection layer is a layer provided between the electrode and the organic layer for lowering the driving voltage and improving the luminance of light emission. There are a hole injection layer and an electron injection layer, and between the anode and the light emitting layer or the hole transport layer. And between the cathode and the light emitting layer or the electron transport layer. The injection layer can be provided as necessary.

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

-Electron blocking layer-
The electron blocking layer has the function of a hole transport layer in a broad sense. By blocking electrons while transporting holes, the probability of recombination of electrons and holes in the light emitting layer can be improved. .
As a material of the electron blocking layer, a known electron blocking layer material can be used, but it is preferable to use a compound represented by the general formula (10). The 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 preventing excitons generated by recombination of holes and electrons in the light emitting layer from diffusing into the charge transport layer. It becomes possible to efficiently confine in the light emitting layer, and the light emission efficiency of the device can be improved. 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.
As a material for the exciton blocking layer, a known exciton blocking layer material can be used, but it is preferable to use a compound represented by the general formula (10).

As the layer adjacent to the light emitting layer, there are a hole blocking layer, an electron blocking layer, an exciton blocking layer, etc., but when these layers are not provided, a hole transport layer, an electron transport layer, etc. Become. It is preferable to use the 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 can be provided as a single layer or a plurality of layers.

The hole transport material has any one of hole injection or transport and electron barrier properties, and may be either organic or inorganic. For the hole transport layer, any known compound can be selected and used. 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, amino-substituted chalcone derivatives. , Oxazole derivatives, styryl anthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline copolymers, and conductive polymer oligomers, particularly thiophene oligomers. Porphyrin derivatives, arylamine derivatives, and styryl 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 can be provided as a single layer or a plurality of layers.

As an electron transport material (which may also serve as a hole blocking material), it is sufficient if it has a function of transmitting electrons injected from the cathode to the light emitting layer. For the electron transport layer, any known compound can be selected and used. For example, polycyclic aromatic derivatives such as naphthalene, anthracene, phenanthroline, tris (8-quinolinolato) aluminum (III) Derivatives, phosphine oxide derivatives, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyrandioxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, bipyridine derivatives, quinoline derivatives, oxadiazole derivatives, benzimidazoles Derivatives, benzothiazole derivatives, indolocarbazole derivatives and the like. Furthermore, 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.

The method for forming each layer when producing the organic EL device of the present invention is not particularly limited, and may be produced by either a dry process or a wet process.

Hereinafter, the present invention will be described in more detail with reference to 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 triflic acid (12.0 g, 104 mmol) was added and stirred at 50 ° C. for 5 hours. Sodium bicarbonate aqueous solution was added and the organic layer was washed with water. Magnesium sulfate was added to the organic layer, dried, filtered, and concentrated to dryness. Further, the solid obtained by recrystallization was purified by sublimation, whereby 1.6 g of a deuterated compound 104 (104D) was obtained.
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 2-8
Compounds 115, 119, 125, 131, 142, 150, or 158 are deuterated in the same manner as in Synthesis Example 1, so that each deuterated compound 115D, 119D, 125D, 131D, 142D, 150D , Or 158D, respectively.

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

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

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

Example 1
Each thin film was laminated at a vacuum degree of 4.0 × 10 ⁻⁵ Pa by a vacuum deposition method on a glass substrate on which an anode made of ITO having a thickness of 70 nm was formed. First, HAT-CN was formed to a thickness of 10 nm as a hole injection layer on ITO, and then HT-1 was formed as a hole transport layer to a thickness of 25 nm. Next, a 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 with a thickness of 30 nm. At this time, co-evaporation was performed under the vapor deposition conditions where the concentration of the compound (104D) was 15 wt%. Next, the 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 to a thickness of 1 nm as an electron injection layer on the electron transport layer. Finally, aluminum (Al) was formed as a cathode to a thickness of 70 nm on the electron injection layer, and an organic EL device was produced.

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 host were changed to the compounds shown in Table 2.

Examples 12 and 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 changed to the compounds shown in Table 2.

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

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

Table 3 shows the maximum emission wavelength, external quantum efficiency, and lifetime of the emission spectrum of the produced organic EL device. The maximum light emission wavelength and external quantum efficiency are values when the drive current density is ^2.5 mA / cm ² , and are initial characteristics. The lifetime was measured as the time required for the luminance to decay to 95% of the initial luminance at an initial luminance of 500 cd / m ² .

From Table 3, the organic EL device using the deuterated TADF material represented by the general formula (1) as the luminescent dopant is superior to the case where the non-deuterated TADF material is used as the luminescent dopant. It can be seen that it has a long life characteristic. This is thought to be due to the fact that the bond-dissociation energy increased due to the deuteration of carbon-hydrogen bonds to carbon-deuterium bonds, and the deterioration of the TADF material due to carbon-hydrogen bond cleavage was suppressed. It is done.

The organic EL element of the present invention is a delayed fluorescence type organic EL element having a high light emission efficiency and a long lifetime, and is practically useful as a display element or a light source element for a display such as a mobile phone.

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

Claims

In an organic electroluminescence device including one or more light emitting layers between an anode and a cathode facing each other, at least one light emitting layer contains a compound represented by the following general formula (1) as a thermally activated delayed fluorescent light emitting material An organic electroluminescent element characterized by comprising:

Here, Z is a condensed aromatic heterocycle represented by formula (2), ring A is an aromatic hydrocarbon ring represented by formula (2a), and ring B is represented by formula (2b). The ring A and the ring B are each fused with an adjacent ring at an arbitrary position.
Ar 1 represents a 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 heterocyclic ring. A linked aromatic group constituted by connecting 2 to 8 aromatic rings of an aromatic group selected from the group, Ar 2 is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, A structure in which 2 to 8 aromatic rings of a substituted or unsubstituted aromatic heterocyclic group having 3 to 18 carbon atoms, or an aromatic group selected from the aromatic hydrocarbon group and the aromatic heterocyclic group are connected Connected aromatic group. When Ar 1 and Ar 2 are linked aromatic groups, the aromatic rings to be linked may be the same or different, and may be linear or branched.
R 1 each independently represents 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, Or 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.
2. The organic electroluminescent device according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by any one of the following general formulas (3) to (8).

Here, Ar 2 , R 1 , a and b have the same meanings as in the general formula (1).
L is a single bond, a 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), 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, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 10 carbon atoms. Or a linked aromatic group constituted by connecting 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.
3. The organic electroluminescence device according to claim 2, which is a compound represented by any one of the general formulas (3) to (6).
4. The organic electroluminescent device according to claim 2, wherein L is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms.
The organic electroluminescent element according to claim 1, wherein the light emitting layer containing the thermally activated delayed fluorescent material contains a host material.
The organic electroluminescence device according to claim 5, wherein the host material is a compound represented by the following general formula (10).

Here, Ar 4 represents a p-valent group generated from benzene, dibenzofuran, dibenzothiophene, carbazole, carborane, triazine, or a compound in which two to three of these are connected.
p represents an integer of 1 or 2, and q represents an integer of 0 to 4. When Ar 4 is a p-valent group derived from benzene, q is an integer of 1 to 4.
The organic electroluminescent element according to claim 5 or 6, comprising at least two kinds of host materials represented by the general formula (10).
8. 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). An organic electroluminescent device according to claim 1.
The organic electroluminescent element 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. .