Materials for organic electroluminescent elements and organic electroluminescent elements

Abstract

An organic EL element having high efficiency and high drive stability is provided, as is an organic EL element material suitable for said element. This material for an organic EL element is formed from an indolocarbazole compound represented by general formula (1). Here, ring a is represented by formula (1a), X is NR, S, O or CR2, Ar1 and Ar2 are aromatic heterocyclic groups represented by formula (1b), the Y's are N or CR, and at least one is N, and L1 is an aromatic hydrocarbon group. This material for an organic EL element is suitable as a material for a hole blocking layer or a host in a light-emitting layer in the organic EL element.

Description

Technical Field

[0001] The present invention relates to a material for an organic electroluminescent element and an organic electroluminescent element using the same.

Background Art

[0002] When a voltage is applied to an organic electroluminescent element (referred to as an organic EL element), holes are injected from the anode and electrons are injected from the cathode into the light-emitting layer, respectively. Then, in the light-emitting layer, the injected holes and electrons recombine to generate excitons. At this time, according to the statistical rule of electron spin, singlet excitons and triplet excitons are generated at a ratio of 1:3. It is said that the internal quantum efficiency of a fluorescent organic EL element using light emission by singlet excitons has a limit of 25%. On the other hand, it is known that the internal quantum efficiency of a phosphorescent organic EL element using light emission by triplet excitons can be increased to 100% when intersystem crossing is efficiently performed from singlet excitons. However, regarding phosphorescent organic EL elements, further improvement in efficiency and low voltage characteristics are technical issues.

[0003] Recently, high-efficiency organic EL elements using delayed fluorescence have been developed. For example, an organic EL element using the TTF (Triplet-Triplet Fusion) mechanism, which is one of the mechanisms of delayed fluorescence, is known. The TTF mechanism utilizes the phenomenon in which singlet excitons are generated by the collision of two triplet excitons, and it is considered that the internal quantum efficiency can be increased to 40% theoretically. However, since the efficiency is lower than that of phosphorescent organic EL elements, further improvement in efficiency is required. Patent Document 1 discloses an organic EL device using a TADF (Thermally Activated Delayed Fluorescence) mechanism. The TADF mechanism utilizes the phenomenon of reverse intersystem crossing from triplet excitons to singlet excitons in materials with a small energy difference between the singlet level and the triplet level, and is theoretically considered to be able to increase the internal quantum efficiency to 100%. However, similar to phosphorescent devices, further improvement in efficiency characteristics and low voltage characteristics are required.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0005] Patent Documents 2 and 3 disclose compounds having two triazine rings. Patent Documents 4 and 5 disclose compounds having two pyrimidine rings and connecting these pyrimidine rings with a phenylene group.

[0006] However, these do not teach the compounds of the present invention, nor do they show the usefulness of organic EL devices using these compounds.

Summary of the Invention

[0007] In order to apply an organic EL element to a display element such as a flat panel display, it is necessary to improve the light emission efficiency of the element and at the same time ensure sufficient stability during driving. In view of the above situation, an object of the present invention is to provide a practically useful organic EL element that realizes high efficiency and low voltage characteristics, and a compound suitable therefor.

[0008] As a result of intensive studies, the present inventors have found that a condensed aromatic heterocyclic compound represented by the following general formula (1) exhibits excellent characteristics when used in an organic EL element, and have completed the present invention.

[0009] The present invention is a material for an organic electroluminescent element comprising a compound represented by general formula (1).

Chemical formula

[0010] Here, ring a is represented by formula (1a), and ring a is condensed with an adjacent ring at an arbitrary position. X is NR 11 , S, O, or CR 12 R 13 is, and R 11 , R 12 , and R 13 each independently represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, or a substituted or unsubstituted linked aromatic group in which 2 to 5 of these aromatic rings are linked. R independently represents hydrogen, deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms. Ar 1 and Ar 2 are independently aromatic heterocyclic groups represented by formula (1b). Ar 3Each independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, or a substituted or unsubstituted linked aromatic group in which 2 to 5 of these aromatic rings are linked. R 14 Each independently represents hydrogen, deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, or a substituted or unsubstituted linked aromatic group in which 2 to 5 of these aromatic rings are linked. Y each independently represents N, or CR 14 and at least one of them is N. L 1 represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms.

[0011] L 1 Examples of L include a phenylene group represented by the following formula (1c) or formula (1d).

Chemical formula

[0012] X can be NR 11 Here, R 11 is the same as R 11 in the general formula (1).

[0013] Examples of the compound represented by the general formula (1) include the compound represented by the general formula (2).

Chemical formula

[0014] More specifically, examples include the compounds represented by any of the general formulas (3) to (8).

Chemical formula

[0015] For the compound represented by the general formula (1), it is desirable that the absolute value of the electron affinity (EA) is greater than 2.6 eV and the absolute value of the ionization potential (IP) is less than 6.1 eV.

[0016] The present invention relates to an organic electroluminescent element in which an anode, an organic layer, and a cathode are laminated on a substrate, and at least one layer of this organic layer is an organic layer containing the above-mentioned material for an organic electroluminescent element.

[0017] The organic layer containing the material for an organic electroluminescent element can be at least one layer selected from the group consisting of a light-emitting layer, an electron transport layer, and a hole-blocking layer.

[0018] The light-emitting layer contains a host and a light-emitting dopant material, and the light-emitting dopant material can be an organometallic complex containing at least one metal selected from the group consisting of ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold. Preferably, the material for an organic electroluminescent element is contained in the light-emitting layer as a host.

[0019] The above-mentioned light-emitting dopant material can also be a thermally activated delayed fluorescence emitting dopant material. Also, a hole-blocking layer can be provided adjacent to the light-emitting layer, and the above-mentioned material for an organic electroluminescent element can be contained in this hole-blocking layer.

[0020] The material for an organic EL element of the present invention has a structure represented by the general formula (1). In a compound having such a structural feature, the lowest unoccupied molecular orbital (LUMO) that affects the electron injection and transport properties of the material is distributed mainly on the nitrogen-containing six-membered ring. Since the compound of the present invention has two or more nitrogen-containing six-membered rings, by changing the number and connection mode of the linking groups existing between the nitrogen-containing six-membered rings, for example, the LUMO orbital can be widened and the electron injection and transport properties of the material can be controlled at a high level, such as increasing the electron injection and transport properties. On the other hand, the highest occupied molecular orbital (HOMO) that affects the hole injection and transport properties of the material is distributed on the condensed aromatic heterocyclic ring typified by indolocarbazole. The spread of the HOMO orbital can be adjusted by changing the condensed ring form of the condensed aromatic heterocyclic ring, the type of substituent, and the position where the substituent is introduced, and the hole injection and transport properties of the material can be controlled at a high level. Because of having the above characteristics, the material of the present invention is a material having both charge (electron and hole) injection and transport properties suitable for the device configuration. By using this in an organic EL element, reduction of the driving voltage of the element and high luminous efficiency can be achieved. In addition, the material for an organic EL element of the present invention exhibits good amorphous characteristics and high thermal stability, and at the same time is extremely stable in the excited state. Therefore, an organic EL element using this has a long driving life and has durability at a practical level.

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

[0022] The material for an organic electroluminescent element of the present invention is represented by the general formula (1). In the general formula (1), ring a is a ring represented by the formula (1a), and this ring a is condensed with an adjacent ring at an arbitrary position.

[0023] Ar 1 and Ar 2is independently an aromatic heterocyclic group represented by the formula (1b). Here, Y is independently N or CR 14 and at least one of them is N. Preferably, at least two of Y in the formula (1b) are N, and more preferably all Y are N.

[0024] R 14 is independently a halogen, deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, or a substituted or unsubstituted linked aromatic group in which 2 to 5 of these aromatic rings are linked. Preferably, it is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms. More preferably, it is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. Further preferably, it is a phenyl group.

[0025] In the present specification, the linked aromatic group refers to a group in which aromatic rings of an aromatic hydrocarbon group or an aromatic heterocyclic group are linked by a single bond, and these may be linked linearly or branchedly, and the aromatic rings may be the same or different.

[0026] Ar 3 is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, or a substituted or unsubstituted linked aromatic group in which 2 to 5 of these aromatic rings are linked, preferably a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, and more preferably a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. The aromatic heterocyclic group preferably contains N, O or S as a heteroatom.

[0027] Ar 3Specific examples in the case where it is an unsubstituted aromatic hydrocarbon group or an unsubstituted aromatic heterocyclic group include groups derived from benzene, naphthalene, anthracene, fluoranthene, phenanthrene, triphenylene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, pyrazine, furan, isoxazole, oxazole, quinoline, isoquinoline, quinoxaline, quinazoline, benzotriazole, phthalazine, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzoisothiazole, benzothiadiazole, dibenzofuran, dibenzothiophene, dibenzoselenophene, benzocarbazole, benzonaphthothiophene, benzonaphthofuran, phenanthroline or carbazole. Preferably, aromatic groups derived from benzene, naphthalene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, oxazole, quinoline, isoquinoline, quinoxaline, quinazoline, phthalazine, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzoisothiazole, or benzothiadiazole, dibenzofuran, dibenzothiophene, or carbazole are mentioned. More preferably, it is a phenyl group which is an aromatic group derived from benzene

[0028] L 1 is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, preferably a p-phenylene group or an m-phenylene group represented by the above formula (1c) or formula (1d). Specific examples in the case of an aromatic hydrocarbon group are the same as those when Ar 3 is an aromatic hydrocarbon group

[0029] X is NR 11 、S, O, or CR 12 R 13 and preferably NR 11 is used

[0030] R 11 、R 12 and R 13 are each independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, or a linked aromatic group in which 2 to 5 of these aromatic rings are linked. Preferably, they are a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, more preferably a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. It is also preferable that the linked aromatic group is one in which 2 to 3 aromatic rings of the aromatic hydrocarbon group having 6 to 10 carbon atoms are linked.

[0031] R independently represents hydrogen, deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, an aromatic hydrocarbon group having 6 to 30 carbon atoms or an aromatic heterocyclic group having 3 to 16 carbon atoms. Preferably, it is hydrogen, deuterium, a phenyl group, or an aromatic heterocyclic group having 3 to 12 carbon atoms. More preferably, it is hydrogen, deuterium, a phenyl group, or a carbazolyl group.

[0032] R, R 14 and Ar 3 are monovalent groups, and when these symbols appear multiple times in the formula, they may be the same or different each time they appear.

[0033] R, R 11 、R 12 、R 13 and R 14 When R, R

[0034] R, R 11 、R 12 、R 13 and R 14 is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, it may be linear, branched or cyclic. Specific examples include methyl, ethyl, propyl, butyl, t-butyl, pentyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl, etc. Preferably, it is an alkyl group having 1 to 4 carbon atoms.Specific examples of the case where it is an aromatic hydrocarbon group or an aromatic heterocyclic group include groups derived from benzene, naphthalene, anthracene, fluoranthene, phenanthrene, triphenylene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, pyrazine, furan, isoxazole, oxazole, quinoline, isoquinoline, quinoxaline, quinazoline, benzotriazole, phthalazine, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzoisothiazole, benzothiadiazole, dibenzofuran, dibenzothiophene, dibenzoselenophene, benzocarbazole, benzonaphthothiophene, benzonaphthofuran, phenanthroline or carbazole. Preferably, aromatic groups derived from benzene, naphthalene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, oxazole, quinoline, isoquinoline, quinoxaline, quinazoline, phthalazine, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzoisothiazole, or benzothiadiazole, dibenzofuran, dibenzothiophene, or carbazole are included. More preferably, it is an aromatic group derived from benzene or carbazole.

[0035] In the present specification, the aromatic hydrocarbon group, the aromatic heterocyclic group, and the linked aromatic ring group can have substituents. Preferred substituents include, in the case of the aromatic hydrocarbon group, the aromatic heterocyclic group, and the linked aromatic ring group, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, deuterium, a halogen, an amino group, a cyano group, and the like.

[0036] As a preferred embodiment of the compound represented by the general formula (1), there is a compound represented by any of the above general formula (2) or general formula (3)(8), and more preferably a compound represented by any of general formulas (3) to (5). In general formulas (2) to (8), the symbols common to general formula (1) have the same meaning.

[0037] Further, it is preferable that the absolute value of the electron affinity (EA) of the compound represented by the general formula (1) is greater than 2.6 eV and the absolute value of the ionization potential (IP) is less than 6.1 eV. The value of IP is the value of the ionization potential (IP) obtained by photoelectron spectroscopy in the thin film obtained by depositing the material, and EA can be calculated using the value of the energy gap obtained from the absorption edge by measuring the absorption spectrum and the value of the IP.

[0038] Specific examples of the compound represented by the general formula (1) are shown below, but are not limited to these exemplified compounds.

[0039]

Chemical formula

Chemical formula

Chemical formula

[0040]

Chemical formula

Chemical formula

Chemical formula

[0041]

Chemical formula

[0042] [Chemical formula] [Chemical formula] [Chemical formula]

[0043] The material for an organic electroluminescent device of the present invention (also referred to as the compound of the present invention, the compound represented by the general formula (1), or an azine compound) is incorporated into at least one organic layer of an organic EL device in which an anode, a plurality of organic layers, and a cathode are laminated on a substrate, thereby providing an excellent organic electroluminescent device. Suitable organic layers for incorporation include a light-emitting layer, an electron transport layer, or a hole-blocking layer. Here, when used in the light-emitting layer, it can be used as a host material for a light-emitting layer containing a fluorescent, delayed fluorescence, or phosphorescent dopant. In addition, the compound of the present invention can be used as an organic light-emitting material that emits fluorescence and delayed fluorescence. The compound of the present invention is particularly preferably incorporated as a host material for a light-emitting layer containing a phosphorescent dopant. When used as an organic light-emitting material that emits fluorescence and delayed fluorescence (also referred to as a thermally activated delayed fluorescence dopant material), it is preferable to use another organic compound having a value of at least one of the singlet excitation energy and the triplet excitation energy higher than that of the compound of the present invention as the host material.

[0044] Next, an organic EL device using the material for an organic electroluminescent device of the present invention will be described.

[0045] The organic EL element of the present invention has an organic layer containing at least one light-emitting layer between an anode and a cathode laminated on a substrate, and at least one organic layer contains the material for an organic electroluminescent element of the present invention. Advantageously, the material for an organic electroluminescent element of the present invention is contained in the light-emitting layer together with a phosphorescent dopant.

[0046] 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 what is shown in the drawings at all.

[0047] FIG. 1 is a cross-sectional view showing an example of the structure of a general organic EL element used in the present invention, where 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is a light-emitting layer, 6 is an electron transport layer, and 7 is a cathode, respectively. In the organic EL element of the present invention, an exciton blocking layer may be provided adjacent to the light-emitting layer, and an electron blocking layer may be provided between the light-emitting layer and the hole injection layer. The exciton blocking layer can be inserted on either the anode side or the cathode side of the light-emitting layer, and it is also possible to insert both at the same time. In the organic EL element of the present invention, the substrate, anode, light-emitting layer, and cathode are essential layers, but it is preferable to have a hole injection / transport layer and an electron injection / transport layer in the layers other than the essential layers, and it is also preferable to have a hole blocking layer between the light-emitting layer and the electron injection / transport layer. Note that the hole injection / transport layer means either one or both of the hole injection layer and the hole transport layer, and the electron injection / transport layer means either one or both of the electron injection layer and the electron transport layer.

[0048] Note that it is also possible to laminate the cathode 7, electron transport layer 6, light-emitting layer 5, hole transport layer 4, and anode 2 in this order on the substrate 1, which is the reverse structure of FIG. 1. Also in this case, it is possible to add or omit layers as necessary.

[0049] - Substrate - The organic EL element of the present invention is preferably supported by a substrate. There is no particular limitation on this substrate, and any substrate that has been conventionally used for organic EL elements may be used. For example, a substrate made of glass, transparent plastic, quartz, etc. can be used.

[0050] - Anode - As the anode in the organic EL element, those using metals, alloys, electrically conductive compounds, and mixtures thereof having a large work function (4 eV or more) as electrode materials are preferably used. Specific examples of such electrode materials include metals such as Au, CuI, indium tin oxide (ITO), SnO2, ZnO, and other conductive transparent materials. Also, materials such as IDIXO (In2O3-ZnO) that can form an amorphous and transparent conductive film may be used. The anode may be formed by forming a thin film of these electrode materials by methods such as vapor deposition or sputtering, and then forming a pattern of a desired shape by photolithography. Alternatively, when the pattern accuracy is not required much (about 100 μm or more), a pattern may be formed through a mask of a desired shape during the vapor deposition or sputtering of the above electrode materials. Or, when a coatable substance such as an organic conductive compound is used, wet film formation methods such as printing or coating can also be used. When extracting light emission from this anode, it is desirable to make the transmittance greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / sq or less. Further, the film thickness depends on the material, but is usually selected in the range of 10 to 1000 nm, preferably 10 to 200 nm.

[0051] - Cathode - On one hand, as the cathode, those using a metal (referred to as an electron-injecting metal) with a small work function (4 eV or less), an alloy, an electrically conductive compound, and a mixture thereof as electrode materials are 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 (Al2O3) mixture, indium, lithium / aluminum mixture, rare earth metals, and the like. Among these, from the viewpoints of electron injection and durability against oxidation, etc., a mixture of an electron-injecting metal and a second metal that is a metal with a larger and more stable work function value than this, for example, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al2O3) mixture, lithium / aluminum mixture, aluminum, etc. are preferable. The cathode can be fabricated by forming a thin film of these electrode materials by methods such as evaporation or sputtering. Also, the sheet resistance as the cathode is preferably several hundred Ω / sq or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm. In addition, in order to transmit the emitted light, it is advantageous for either the anode or the cathode of the organic EL element to be transparent or translucent as the emission luminance will be improved.

[0052] Also, after fabricating the above metal on the cathode with a film thickness of 1 to 20 nm, a conductive transparent material mentioned in the description of the anode is fabricated thereon, whereby a transparent or translucent cathode can be fabricated, and by applying this, an element in which both the anode and the cathode have permeability can be fabricated.

[0053] -Light-emitting layer- The light-emitting layer is a layer that emits light after excitons are generated by the recombination of holes and electrons injected from the anode and the cathode respectively, and the light-emitting layer contains an organic light-emitting material and a host material. When the light-emitting layer is a fluorescent light-emitting layer, the fluorescent light-emitting material may use at least one fluorescent light-emitting material alone, but it is preferable to use the fluorescent light-emitting material as a fluorescent light-emitting dopant and contain a host material.

[0054] As the fluorescent light-emitting material in the light-emitting layer, an azine compound represented by the general formula (1) can be used, and since many patent documents and the like are known, it can also be selected from them. For example, benzoxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, styrylbenzene derivatives, polyphenyl derivatives, diphenylbutadiene derivatives, tetraphenylbutadiene derivatives, naphthalimide derivatives, coumarin derivatives, condensed aromatic compounds, perinone derivatives, oxadiazole derivatives, oxazine derivatives, aldazine derivatives, cyclopentadiene derivatives, bisstyrylanthracene derivatives, quinacridone derivatives, pyrrolopyridine derivatives, thiadiazolopyridine derivatives, styrylamine derivatives, diketopyrrolopyrrole derivatives, aromatic dimethylidine compounds, metal complexes of 8-quinolinol derivatives and metal complexes of pyromethene derivatives, various metal complexes typified by rare earth complexes and transition metal complexes, polymer compounds such as polythiophene, polyphenylene, polyphenylene vinylene, and organic silane derivatives. Preferred are condensed aromatic compounds, styryl compounds, diketopyrrolopyrrole compounds, oxazine compounds, pyromethene metal complexes, transition metal complexes, and lanthanoid complexes. More preferred are naphthalene, pyrene, chrysene, triphenylene, benzo[c]phenanthrene, benzo[a]anthracene, pentacene, perylene, fluoranthene, acenaphthofluoranthene, dibenzo[a,j]anthracene, dibenzo[a,h]anthracene, benzo[a]naphthacene, hexacene, anthantrene, naphtho[2,1-f]isoquinoline, α-naphthaphenanthridine, phenanthrooxazole, quinolino[6,5-f]quinoline, benzothiophenthrene, etc. These may have an alkyl group, an aryl group, an aromatic heterocyclic group, or a diarylamino group as a substituent.

[0055] As the fluorescent host material in the light-emitting layer, in addition to being able to use an azine compound represented by the general formula (1), since it is known from a number of patent documents and the like, it can also be selected from them. For example, compounds having a condensed aryl ring such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, perylene, fluoranthene, fluorene, indene and derivatives thereof, aromatic amine derivatives such as N,N'-dinaphthyl-N,N'-diphenyl-4,4'-diphenyl-1,1'-diamine, metal chelated oxynoid compounds such as tris(8-quinolinato)aluminum(III), bisstyryl derivatives such as distyrylbenzene derivatives, tetraphenylbutadiene derivatives, indene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, pyrrolopyrrole derivatives, thiadiazolopyridine derivatives, dibenzofuran derivatives, carbazole derivatives, indolocarbazole derivatives, triazine derivatives, and in the polymer system, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, polythiophene derivatives, etc. can be used, but are not particularly limited.

[0056] When the fluorescent light-emitting material is used as a fluorescent light-emitting dopant and a host material is included, the amount of the fluorescent light-emitting dopant contained in the light-emitting layer is preferably in the range of 0.01 to 20% by weight, more preferably 0.1 to 10% by weight.

[0057] Generally, in an organic EL element, charges are injected from both electrodes, the anode and the cathode, into a light-emitting material to generate an excited light-emitting material in an excited state and cause it to emit light. In the case of a charge-injection type organic EL element, it is said that among the generated excitons, 25% are excited to the singlet excited state and the remaining 75% are excited to the triplet excited state. As shown in Advanced Materials 2009, 21, 4802-4806, specific fluorescent light-emitting materials are known to emit thermally activated delayed fluorescence by reverse intersystem crossing to the singlet excited state and emitting fluorescence after the energy transitions to the triplet excited state due to intersystem crossing or the like and then undergoing triplet-triplet annihilation or absorption of thermal energy. The organic EL element of the present invention can also exhibit delayed fluorescence. In this case, both fluorescent light emission and delayed fluorescent light emission can be included. However, part or a portion of the light emission may be from the host material.

[0058] When the light-emitting layer is a delayed fluorescence light-emitting layer, at least one kind of delayed fluorescence material may be used alone, but it is preferable to use the delayed fluorescence material as a delayed fluorescence light-emitting dopant and include a host material.

[0059] As the delayed fluorescence light-emitting material in the light-emitting layer, when the azine compound represented by the general formula (1) is a material having a small energy difference between the singlet level and the triplet level, this can be used, but it can also be selected from known delayed fluorescence light-emitting materials. For example, tin complexes, indolocarbazole derivatives, copper complexes, carbazole derivatives, etc. can be mentioned. Specifically, the compounds described in the following non-patent documents and patent documents can be mentioned, but the present invention is not limited to these compounds.

[0060] 1) Adv. Mater. 2009, 21, 4802-4806, 2) Appl. Phys. Lett. 98, 083302 (2011), 3) JP 2011-213643 A, 4) J. Am. Chem. Soc. 2012, 134, 14706-14709.

[0061] Specific examples of the delayed fluorescence material are shown, but it is not limited to the following compounds. [Chemical formula]

[0062] When the delayed fluorescence material is used as a delayed fluorescence dopant and a host material is included, the amount of the delayed fluorescence dopant contained in the light-emitting layer is preferably in the range of 0.01 to 50% by weight, more preferably 0.1 to 20% by weight, and even more preferably 0.01 to 10%.

[0063] As the delayed fluorescence host material in the light-emitting layer, an azine compound represented by the general formula (1) can be used, but it can also be selected from other compounds. For example, compounds having a condensed aryl ring such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, perylene, fluoranthene, fluorene, indene, and their derivatives, aromatic amine derivatives such as N,N'-dinaphthyl-N,N'-diphenyl-4,4'-diphenyl-1,1'-diamine, metal chelated oxynoid compounds such as tris(8-quinolinato)aluminum(III), bisstyryl derivatives such as distyrylbenzene derivatives, tetraphenylbutadiene derivatives, indene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, pyrrolopyrrole derivatives, thiadiazolopyridine derivatives, dibenzofuran derivatives, carbazole derivatives, indolocarbazole derivatives, triazine derivatives, and in the polymer system, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, polythiophene derivatives, arylsilane derivatives, etc. can be used, but it is not limited thereto.

[0064] When the light-emitting layer is a phosphorescent light-emitting layer, the light-emitting layer contains a phosphorescent dopant and a host material. As the phosphorescent dopant material, those containing an organometallic complex containing at least one metal selected from ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold are preferable.

[0065] Preferable phosphorescent dopants include complexes such as Ir(ppy)3 having a noble metal element such as Ir as a central metal, complexes such as Ir(bt)2·acac3, and complexes such as PtOEt3. Specific examples of these complexes are shown below, but are not limited to the following compounds.

[0066]

Chemical formula

[0067] The amount of the phosphorescent dopant contained in the light-emitting layer is preferably in the range of 2 to 40% by weight, more preferably 5 to 30% by weight.

[0068] When the light-emitting layer is a phosphorescent light-emitting layer, it is preferable to use the azine compound of the present invention as the host material in the light-emitting layer. However, when the azine compound is used in any other organic layer than the light-emitting layer, other host materials may be used. Also, the compound of the present invention and other host materials may be used in combination. Furthermore, a plurality of known host materials may be used in combination. As the known host compound, it is preferably a compound having a hole-transporting ability, an electron-transporting ability, preventing the shift of emission to a longer wavelength, and having a high glass transition temperature.

[0069] Such other host materials are known from a number of patent documents and the like, 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, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidene compounds, porphyrin compounds, anthraquinodimethane derivatives, anthrone derivatives, diphenylquinone derivatives, thiopyrandioxide derivatives, heterocyclic tetracarboxylic anhydrides such as naphthalene perylene, phthalocyanine derivatives, metal complexes of 8-quinolinol derivatives and metal phthalocyanines, various metal complexes typified by metal complexes of benzoxazole and benzothiazole derivatives, polysilane compounds, poly(N-vinylcarbazole) derivatives, aniline copolymers, thiophene oligomers, polythiophene derivatives, polyphenylene derivatives, polyphenylene vinylene derivatives, polyfluorene derivatives and other polymer compounds.

[0070] The light-emitting layer may be any of a fluorescent light-emitting layer, a delayed fluorescence light-emitting layer or a phosphorescent light-emitting layer, but is preferably a phosphorescent light-emitting layer.

[0071] - Injection layer - The injection layer is a layer provided between the electrode and the organic layer to reduce the driving voltage and improve the light-emitting luminance. There are a hole injection layer and an electron injection layer, which may be present 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 needed.

[0072] - Hole blocking layer - The hole-blocking layer, in a broad sense, has the function of an electron transport layer. It is composed of a hole-blocking material that has the function of transporting electrons while having extremely low ability to transport holes, and can improve the recombination probability of electrons and holes by transporting electrons while blocking holes.

[0073] It is preferable to use the azine compound of the present invention for the hole-blocking layer. However, when using it in any other organic layer, a known hole-blocking layer material may be used. Further, as the hole-blocking layer material, the material of the electron transport layer described later can be used as needed.

[0074] - Electron-blocking layer - The electron-blocking layer is composed of a material that has the function of transporting holes while having extremely low ability to transport electrons, and can improve the probability of recombination of electrons and holes by transporting holes while blocking electrons.

[0075] As the material of the electron-blocking layer, the material of the hole transport layer described later can be used as needed. The film thickness of the electron-blocking layer is preferably 3 to 100 nm, more preferably 5 to 30 nm.

[0076] - 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. By inserting this layer, excitons can be efficiently confined in the light-emitting layer, and the light-emitting efficiency of the device can be improved. The exciton-blocking layer can be inserted adjacent to the light-emitting layer on either the anode side or the cathode side, or both can be inserted simultaneously.

[0077] As the material of the exciton-blocking layer, the material of the hole transport layer and the electron transport layer described later can be used as needed. Also, the azine compound represented by the general formula (1) can be used. Other materials include, for example, 1,3-dicarbazolylbenzene (mCP) and bis(2-methyl-8-quinolinolato)-4-phenylphenolatoaluminum(III) (BAlq).

[0078] - Hole transport layer - The hole transport layer is composed of a hole transport material having a function of transporting holes, and the hole transport layer can be provided as a single layer or multiple layers.

[0079] The hole transport material has either a function of injecting or transporting holes or a function of blocking electrons, and can be either an organic or inorganic material. As known hole transport materials that can be used, any one of these can be selected and used. Known hole transport materials that can be used include, for example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline-based copolymers, and conductive polymer oligomers, particularly thiophene oligomers, etc. However, it is preferable to use porphyrin compounds, aromatic tertiary amine compounds, and styrylamine compounds, and it is more preferable to use aromatic tertiary amine compounds. In addition, an azine compound represented by the general formula (1) can be used as the hole transport material.

[0080] - Electron transport layer - The electron transport layer is composed of a material having a function of transporting electrons, and the electron transport layer can be provided as a single layer or multiple layers.

[0081] As the electron transport material (which may also serve as a hole blocking material), it suffices to have the function of transmitting the electrons injected from the cathode to the light emitting layer. Although the azine compound of the present invention can be used for the electron transport layer, any one can be selected from conventionally known compounds and used. For example, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyrandioxide derivatives, carbodiimide, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, oxadiazole derivatives and the like can be mentioned. Further, among the above oxadiazole derivatives, thiadiazole derivatives in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and quinoxaline derivatives having a quinoxaline ring known as an electron-withdrawing group can also be used as the electron transport material. Furthermore, a polymer material in which these materials are introduced into a polymer chain or a polymer material having these materials as the main chain of the polymer can also be used. It is preferable that the difference in the electron affinity (EA) between the electron transport material (including the case where it also serves as a hole blocking material) and the organic light-emitting dopant material or host is 0.3 eV.

Example

[0082] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples and can be implemented in various forms as long as the gist thereof is not exceeded.

[0083] An azine compound as a material for an organic electroluminescent device was synthesized according to the route shown below. The compound numbers correspond to the numbers attached to the above chemical formulas.

[0084] Example 1 Compounds 1-6 were synthesized according to the following reaction formula.

Chemical formula

[0085] Example 2 Compound 1-7 was synthesized according to the following reaction formula.

Chemical formula

[0086] Example 3 Compound 1-16 was synthesized according to the following reaction formula.

Chemical formula

[0087] Example 4 Compound 1-137 was synthesized according to the following reaction formula.

Chemical formula

[0088] In accordance with the above synthesis examples, in addition to compounds 1-6, 1-7, 1-16, and 1-137, compounds 1-1, 1-5, 1-12, 1-27, 1-28, and 1-198 were synthesized. Also, compounds H-1, H-2, H-3, and H-4 for comparison were synthesized.

[0089]

Chemical formula

[0090] The measured values of the ionization potential (IP) in this specification are obtained by photoelectron spectroscopy on a thin film of the host material. The measured value of the electron affinity (EA) can be calculated using the value of the ionization potential and the value of the energy gap obtained from the absorption spectrum measured from its absorption edge.

[0091] Table 1 shows the absolute values of the electron affinity (EA) and ionization potential (IP) of Compounds 1-6, 1-7, 1-16, 1-137 and H-1, H-2, H-3, H-4.

Table 1

[0092] Example 5 On a glass substrate on which an anode made of ITO with a thickness of 110 nm was formed, each thin film was deposited by vacuum evaporation at a vacuum degree of 4.0×10 -5 Pa. First, CuPc was formed as a hole injection layer on the ITO with a thickness of 25 nm, and then NPD was formed as a hole transport layer with a thickness of 30 nm. Next, HT-1 was formed as an electron blocking layer with a thickness of 10 nm. Next, Compound 1-1 as a host material and Ir(ppy)3 as a light-emitting dopant were co-evaporated from different evaporation sources to form a light-emitting layer with a thickness of 40 nm. At this time, the concentration of Ir(ppy)3 was 10 wt%. Further, H-3 was formed as a hole blocking layer with a thickness of 10 nm. Next, ET-1 was formed as an electron transport layer with a thickness of 10 nm. Further, LiF was formed as an electron injection layer with a thickness of 1 nm on the electron transport layer. Finally, Al was formed as a cathode with a thickness of 70 nm on the electron injection layer to fabricate an organic EL element. When an external power source was connected to the obtained organic EL element and a DC voltage was applied, an emission spectrum with a peak wavelength of 517 nm was observed, indicating that the emission from Ir(ppy)3 was obtained.

[0093] Examples 6 to 14 As an organic EL device was fabricated in the same manner as in Example 5, except that compounds 1-5, 1-6, 1-7, 1-12, 1-16, 1-27, 1-28, 1-137, and 1-198 were used as the host materials for the light-emitting layer instead of compound 1-1. When an external power source was connected to the obtained organic EL device and a DC voltage was applied, an emission spectrum with a peak wavelength of 517 nm was observed.

[0094] Comparative Examples 1 to 2 An organic EL device was fabricated in the same manner as in Example 5, except that H-1 and H-3 were used as the host materials for the light-emitting layer in Example 5. When an external power source was connected to the obtained organic EL device and a DC voltage was applied, an emission spectrum with a peak wavelength of 517 nm was observed.

[0095] The evaluation results of the fabricated organic EL devices are shown in Table 2. In the table, the luminance, driving voltage, and luminous efficiency are the values at a driving current of 20 mA / cm 2 and are the initial characteristics. LT70 is the time required for the initial luminance to decay to 70% and represents the lifetime characteristics.

[0096]

Table 2

[0097] Example 15 On a glass substrate on which an anode made of ITO with a film thickness of 110 nm was formed, each thin film was deposited by vacuum evaporation at a vacuum degree of 4.0×10 -5It was laminated at Pa. First, CuPc was formed as a hole injection layer on ITO with a thickness of 25 nm, and then NPD was formed as a hole transport layer with a thickness of 45 nm. Next, HT-1 was formed as an electron blocking layer with a thickness of 10 nm. Then, compound 1-1 as a host material and Ir(piq)2acac as a dopant were co-evaporated from different evaporation sources to form a light-emitting layer with a thickness of 40 nm. At this time, the concentration of Ir(piq)2acac was 6.0 wt%. Further, H-3 was formed as a hole blocking layer with a thickness of 10 nm. Next, ET-1 was formed as an electron transport layer with a thickness of 27.5 nm. And LiF was formed as an electron injection layer with a thickness of 1 nm on the electron transport layer. Finally, Al was formed as a cathode with a thickness of 70 nm on the electron injection layer to fabricate an organic EL device. When an external power supply was connected to the obtained organic EL device and a DC voltage was applied, an emission spectrum with a peak wavelength of 620 nm was observed, indicating that light emission from Ir(piq)2acac was obtained.

[0098] Examples 16 to 24 An organic EL device was fabricated in the same manner as in Example 15, except that compounds 1-5, 1-6, 1-7, 1-12, 1-16, 1-27, 1-28, 1-137, and 1-198 were used as the host materials for the light-emitting layer instead of compound 1-1. When a DC voltage was applied to the obtained organic EL device, an emission spectrum with a peak wavelength of 620 nm was observed. 15 When a DC voltage was applied to the obtained organic EL device, an emission spectrum with a peak wavelength of 620 nm was observed.

[0099] Comparative Examples 3 to 5 An organic EL device was fabricated in the same manner as in Example 15, except that H-1, H-2, and H-3 were used as the host materials for the light-emitting layer. When a DC voltage was applied to the obtained organic EL device, an emission spectrum with a peak wavelength of 620 nm was observed. 15 When a DC voltage was applied to the obtained organic EL device, an emission spectrum with a peak wavelength of 620 nm was observed.

[0100] The evaluation results of the fabricated organic EL devices are shown in Table 3. The evaluation conditions are the same as those in Examples 5 to 14, where LT90 is the time required for the initial luminance to decay to 90%.

[0101]

Table 3

[0102] It can be seen from Tables 2 and 3 that Examples 5 to 24 have improved power efficiency and life characteristics and exhibit good characteristics.

[0103] Example 25 On a glass substrate on which an anode made of ITO with a film thickness of 110 nm was formed, each thin film was laminated by a vacuum evaporation method at a degree of vacuum of 4.0×10 -5 Pa. First, CuPc was formed as a hole injection layer on the ITO to a thickness of 25 nm, and then NPD was formed as a hole transport layer to a thickness of 30 nm. Next, HT-1 was formed as an electron blocking layer to a thickness of 10 nm. Next, compound H-1 as a host material and Ir(ppy)3 as a light-emitting dopant were co-evaporated from different evaporation sources to form a light-emitting layer to a thickness of 40 nm. At this time, the concentration of Ir(ppy)3 was 10 wt%. Further, compound 1-1 was formed as a hole blocking layer to a thickness of 5 nm. Next, ET-1 was formed as an electron transport layer to a thickness of 15 nm. Further, LiF was formed as an electron injection layer on the electron transport layer to a thickness of 1 nm. Finally, Al was formed as a cathode on the electron injection layer to a thickness of 70 nm to fabricate an organic EL element.

[0104] Examples 26 to 34 An organic EL element was fabricated in the same manner as in Example 25, except that compounds 1-5, 1-6, 1-7, 1-12, 1-16, 1-27, 1-28, 1-137, and 1-198 were used instead of compound 1-1 as the hole blocking layer in Example 25.

[0105] Example 35 An organic EL element was fabricated in the same manner as in Example 25, except that compound 1-1 was used instead of H-1 as the host material of the light-emitting layer in Example 25.

[0106] Comparative Examples 6 to 7 An organic EL element was fabricated in the same manner as in Example 25, except that H-1 and H-3 were used as the hole blocking layer in Example 25.

[0107] Table 4 shows the evaluation results of the fabricated organic EL elements.

[0108]

Table 4

[0109] The compounds used in the examples are shown below.

Chemical formula

Claims

1. A material for an organic electroluminescent device contained in at least one organic layer of an organic electroluminescent device in which an anode, a plurality of organic layers, and a cathode are laminated on a substrate, the material consisting of a compound represented by any of general formulas (3) to (8), and the organic layer containing the material for an organic electroluminescent device being any selected from the group consisting of a light-emitting layer, an electron transport layer, and a hole-blocking layer. 【Chemical Formula 1】 【Chemical Formula 2】 【Chemical Formula 3】 (Here, each R independently represents hydrogen, deuterium, a phenyl group, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms. R １５ represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 16 carbon atoms, or a substituted or unsubstituted linked aromatic group in which 2 to 5 of these aromatic rings are linked. Ar ２ independently represents an aromatic heterocyclic group represented by formula (1b), Ar ３ independently represents hydrogen, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms. Y independently represents N or CR １４ and at least one of them is N. R １４ independently represents hydrogen, deuterium, or a substituted or unsubstituted aromatic hydrocarbon group having 6 carbon atoms. L １ represents a substituted or unsubstituted phenylene group. Here, when the aromatic hydrocarbon group, aromatic heterocyclic group, or linked aromatic ring group has a substitution, the substituent is selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, deuterium, a halogen, an amino group, and a cyano group.)

2. L １The material for an organic electroluminescent device according to claim 1, wherein is a phenylene group represented by the following formula (1c) or formula (1d). 【Chemical 4】

3. The material for an organic electroluminescent device according to claim 1 or 2, which is a compound represented by any of general formulas (3) to (5).

4. An organic electroluminescent device in which an anode, a plurality of organic layers, and a cathode are laminated on a substrate, wherein at least one of the organic layers contains the material for an organic electroluminescent device according to any of claims 1 to 3, and the organic layer containing the material for an organic electroluminescent device is any one selected from the group consisting of a light-emitting layer, an electron transport layer, and a hole-blocking layer.

5. The organic electroluminescent device according to claim 4, wherein the organic layer containing the material for an organic electroluminescent device is a light-emitting layer.

6. The light-emitting layer contains a host and a light-emitting dopant material, and the light-emitting dopant material is an organometallic complex containing at least one metal selected from the group consisting of ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold. The organic electroluminescent device according to claim 5.

7. The light-emitting layer contains a host and a light-emitting dopant material, and the light-emitting dopant material is a thermally activated delayed fluorescence emitting dopant material. The organic electroluminescent device according to claim 5.

8. The organic electroluminescent device according to any of claims 4 to 7, wherein a hole-blocking layer is provided adjacent to the light-emitting layer, and the material for an organic electroluminescent device described above is contained in the hole-blocking layer.

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