JP2000021571A - Organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light emitting efficiency, and to maintain a stable light emitting characteristic over a long period by including an anthracene compound in an organic light emitting layer. SOLUTION: A compound expressed by the formula is included in a light emitting layer of an organic EL element. In the formula, R1 and R2 respectively independently represent either of hydrogen, a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic hydrocarbon radical and an aromatic heterocyclic group. X1 and X2 represent an oxygen atom, a sulfur atom, a selenium atom, a tellurium atom and an ethynyl group. (m and n) are 1 or 2. An aromatic condensed ring being a basic skeleton decided by (m, n) has anthracene in (m=n-1), naphthacene in (m+n=3 (m=1, n=2 or m=2, n=1)) and pentacene in (m=n=1). A substance having high carrier transportability and a high fluorescent quantum yield is desirable as this compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence (organic EL) device used for a flat display or a flat light source, and more particularly, to an organic EL device having improved light emission characteristics and excellent life characteristics. It is about.

[0002]

2. Description of the Related Art With the rapid progress of technological development in the field of information communication in recent years, great expectations have been placed on flat displays instead of CRTs. Among them, EL elements have been actively studied since they are excellent in high-speed response, visibility, luminance, and the like.

At present, a practically used ZnS / Mn-based inorganic EL device has a problem that the driving voltage is as high as about 100 V and sufficient luminance cannot be obtained. On the other hand, the electroluminescence of organic fluorescent substances has been known for a long time, and many studies using an anthracene single crystal have been conducted.However, since the driving voltage is high and the emission luminance is low, it has not been possible to develop a practical device. Did not.

[0004] However, in 1987, Kodak T
The organic EL device disclosed by Ang et al. can be driven at a low DC voltage of 10 V or less, has a high luminance of 1000 cd / m ^2, and has an excellent luminous efficiency of 1.5 lm / W (Appl. Phys. Lett., 51, 913 (1987)). This presentation showed the advantages of low-voltage driving and multi-coloring by designing organic molecules compared to inorganic EL devices, and the research of many organic EL devices such as new organic materials and new cathode materials was demonstrated. Began to take place.

[0005]

As a conventionally known organic material for the light emitting layer, there is tris (8-quinolinolato) aluminum (hereinafter abbreviated as "Alq"). Using this Alq as a host material for the light emitting layer, a coumarin derivative (see JP-A-3-792), a dicyanomethylene derivative (see JP-A-3-162481), and a quinacridone derivative (see JP-A-5-70773). Attempts have been made to improve the luminous efficiency by doping a fluorescent organic dye material such as However, the life is not always satisfactory, and the development of an organic EL device having higher luminous efficiency and longer life has been desired.

An object of the present invention has been made in view of the above circumstances of the prior art, and an object of the present invention is to provide an organic EL device capable of improving luminous efficiency and maintaining stable luminous characteristics for a long period of time. It is in.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an organic electroluminescence device having at least an anode, a light-emitting layer containing an organic light-emitting substance, and a cathode. Provided is an organic EL device, wherein the layer contains a compound represented by the following general formula (1).

[0008]

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(Wherein R ^{1 and} R ² are each independently hydrogen, a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic group, X ¹ and X ² each independently represents any one of an oxygen atom, a sulfur atom, a selenium atom, a tellurium atom, and an ethynyl group; Or 2, respectively, and a part of the hydrogen atoms of the aromatic condensed ring defined by m and n is a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group. Or an aromatic hydrocarbon group, a phenylethynyl group, or an aromatic heterocyclic group.)

Also, a hole transport layer is provided between the anode and the light emitting layer containing an organic light emitting substance, and the hole transport layer provides an organic EL device containing the compound represented by the general formula (1). I do.

In the compound of the general formula (1), X ¹ and X ² each independently represent any one of an oxygen atom, a sulfur atom and an ethynyl group, and m + n represents 2 or 3.
an organic EL device which is a compound represented by the formula: wherein a part of the hydrogen atoms of the aromatic condensed ring defined by m and n may be substituted with an aryl group, an aryloxy group, an aromatic hydrocarbon group or a phenylethynyl group. I will provide a.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a light emitting layer of an organic EL device contains a compound represented by the general formula (1). As a result, an organic EL device having excellent luminous efficiency and capable of emitting light stably for a long period of time is obtained.

A hole transport layer is provided between the anode and the light emitting layer of the organic EL device, and the hole transport layer contains the compound represented by the general formula (1). As a result, the organic EL has excellent luminous efficiency and can emit light stably for a long period of time.
An element is obtained.

FIG. 1 is a side view of the basic structure of the organic EL device of the present invention, and FIG. 2 is a side view of a more preferred example. In FIG. 1, 1 is a substrate, 2 is an anode, 3 is a light emitting layer containing an organic light emitting substance, and 4 is a cathode. FIG. 2 shows a state in which a hole transport layer 5 and an interface layer 6 are provided between the anode 2 and the light emitting layer 3, and an electron transport layer 7 and an interface layer 8 are provided between the cathode 4 and the light emitting layer 3. ing.

The substrate 1 in the present invention is a support for an organic EL device, and a transparent substrate such as glass or plastic is generally used. In the case of plastic, polycarbonate, polymethacrylate, polysulfone, or the like can be used.

On the substrate 1, a transparent electrode as the anode 2 is provided. As the transparent electrode, an indium tin oxide (ITO) thin film or a tin oxide film can be usually used. In addition, metals having a large work function, such as aluminum and gold, inorganic conductive substances such as copper iodide, and poly (3-
(Methylthiophene), polypyrrole, and polyaniline.

The method of producing the anode is generally performed by a vacuum deposition method, a sputtering method, or the like. In the case of a conductive polymer, a solution with an appropriate binder is applied to the substrate. Alternatively, a thin film can be formed directly on a substrate by electrolytic polymerization. The thickness of the anode depends on the required transparency, but the visible light transmittance is 60% or more, preferably 80% or more.
It is 5 to 1000 nm, preferably 10 to 500 nm.

A light emitting layer 3 is provided on the anode 2. As the organic light emitting substance of the light emitting layer, a compound having a high fluorescence quantum yield, a high electron injection efficiency from the cathode 4, and a high electron mobility is effective. In particular, a chelate complex of a quinoline derivative which is excellent in stability and heat resistance in an amorphous thin film can be preferably used.

The metal element forming such a chelate complex includes lithium, silver, beryllium, magnesium, calcium, strontium, zinc, cadmium,
Examples include aluminum, gallium, indium, thallium, yttrium, scandium, lanthanum, zirconium, manganese, and lutetium. Among them, chelate complexes of beryllium, magnesium, aluminum, calcium, zinc, scandium and the like having high fluorescence quantum yield are particularly preferable.

The thickness of the light emitting layer 3 is usually 10 to
It is 200 nm, preferably 40 to 100 nm.

In the present invention, at least the compound represented by the general formula (1) is contained in the light-emitting layer in order to improve the light-emitting efficiency of the device and maintain high light-emitting efficiency for a long period of time.

[0022]

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(Wherein R ^{1 and} R ² each independently represent hydrogen, a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic group, X ¹ and X ² each independently represents any one of an oxygen atom, a sulfur atom, a selenium atom, a tellurium atom, and an ethynyl group; Or 2, respectively, and a part of the hydrogen atoms of the aromatic condensed ring defined by m and n is a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group. Or an aromatic hydrocarbon group, a phenylethynyl group, or an aromatic heterocyclic group.)

The compound represented by the general formula (1) of the present invention is an aromatic condensed ring serving as a basic skeleton defined by m and n, when m = n = 1, anthracene and m + n =
3 (m = 1, n = 2 or m = 2, n = 1) has naphthacene, and m = n = 1 has pentacene.

The compound of the general formula (1) of the present invention includes:
In order to suppress the accumulation of carriers in the light emitting layer and the hole transport layer and facilitate energy transfer from excitons, a substance having a high carrier transport property and a high fluorescence quantum yield is preferable.

In such a substance, X ¹ and X ² each independently represent any one of an oxygen atom, a sulfur atom and an ethynyl group, anthracene when m = n = 1, and m + n = 3
(M = 1, n = 2 or m = 2, n = 1), it is preferably either naphthacene. Further, when a part of the hydrogen atoms of the aromatic condensed ring determined by m and n is substituted, it is preferable to substitute an aryl group, an aryloxy group, an aromatic hydrocarbon group, or a phenylethynyl group.

The compound represented by the general formula (1) may be contained in the organic light emitting layer in an amount of 0.01 to 30 mol%, particularly preferably 0.5 to 10 mol%. When the content is 0.5 mol% or more, energy transfer from a singlet exciton easily occurs. When the content is 10 mol% or less, a decrease in emission luminance due to concentration quenching and an increase in driving voltage due to an increase in electron injection barrier are caused. Extremely low.

When a hole transport layer is provided between the anode and the light emitting layer, the above effect can be sufficiently obtained even if the hole transport layer contains the compound represented by the general formula (1). be able to. The compound represented by the general formula (1) may be contained in the hole transport layer in an amount of 0.01 to 30 mol%, particularly preferably 0.5 to 10 mol%, for the above-described reason.

Further, by including the compound of the general formula (1) in both the hole transport layer and the light emitting layer, it is possible to further improve the light emitting efficiency and maintain the high light emitting efficiency for a long period of time.

In the present invention, as a method for further improving the luminous efficiency of the device and enabling a full-color display,
The organic luminescent layer can be doped with another fluorescent organic material simultaneously with the compound represented by the general formula (1).

As such a doped dye material, known organic substances can be used, and examples thereof include stilbene dyes, oxazole dyes, cyanine dyes, xanthene dyes, oxazine dyes, coumarin dyes, and acridine dyes. Dyes, quinacridone derivatives, perylene derivatives (JP-A-3-791), 4-dicyanomethylene-
2-methyl-6-p-dimethylaminostyryl-4H-
Pyran (DCM1) derivative, europium (III) complex (Chem. Lett., 1991, 1267), zinc porphyrin derivative,
Rhodamine dyes (JP-A-8-286033),
It can be widely used such as a biolanthrone derivative (JP-A-7-90259), a neil red derivative, a bis (2-styryl-8-quinolinolato) zinc (II) complex (Chem. Lett., 1997, 633). The concentration of such a doped organic material is 0.01 to 30 mol in the light emitting layer.
%.

In the present invention, the anode 2 and the organic light emitting layer 3
A hole transport layer 5 can be provided between the layers as needed. By providing the hole transport layer, electrons injected from the cathode and traveling in the light emitting layer are efficiently blocked, and high luminous efficiency can be achieved.

As such a hole transport material, the anode 2
A material having a low injection barrier from holes and a high hole mobility can be used. As such a hole transport material, a known hole transport material can be used. For example, N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,
Aromatic diamine compounds such as 1'-biphenyl-4,4'-diamine (hereinafter referred to as TPD) and 1,1'-bis (4-di-p-tolylaminophenyl) cyclohexane;
The hydrazone compound disclosed in JP-A-2-311591 can be used.

Further, polymer materials such as poly-N-vinylcarbazole and polysilane can also be preferably used (Appl. Phys. Lett., 59, 2760 (1991)).

The thin film of the organic hole transporting material can be formed by vacuum deposition, dipping, spin coating, L
Various methods such as the method B can be applied. In order to produce a uniform thin film of submicron order without defects such as pinholes, a vacuum evaporation method and a spin coating method are particularly preferable.

In the case of spin coating, a binder resin that does not trap holes can be used by dissolving it in a coating solution. Examples of such a binder resin include polyether sulfone, polycarbonate, and polyester. The content of the binder resin is preferably from 10 to 50% by weight which does not decrease the hole mobility.

The material of the hole transporting layer is not limited to the above-mentioned organic substances, but may be a metal chalcogenide, a metal halide, a metal carbide, a nickel oxide, a lead oxide, a copper iodide, a lead sulfide, or the like. A type compound semiconductor, p-type hydrogenated amorphous silicon, p-type hydrogenated amorphous silicon carbide, or the like can also be used.

The hole transport layer of such an inorganic substance can be formed by a known method such as a vacuum evaporation method, a sputtering method, and a CVD method. Regardless of whether an organic substance or an inorganic substance is used, the thickness of the hole transport layer is usually
10 to 200 nm, preferably 20 to 80 nm
It is.

In the present invention, the anode 2 and the hole transport layer 5
In order to prevent leakage current, reduce a hole injection barrier, improve adhesion, and the like, an interface layer 6 can be provided to reduce the drive voltage and extend the life.

Such an interface layer material is disclosed in
4,4 ', 4 "-tris @ N- (3
-Methylphenyl) -N-phenylamino-triphenylamine (hereinafter referred to as MTDATA), 4,4 ', 4 "
-Tris {N, N diphenylamino} triphenylamine (hereinafter referred to as TDATA), copper phthalocyanine and the like can be preferably used. The film thickness when providing this interface layer is:
It can be preferably used at 5 to 100 nm.

On the light emitting layer 3, a cathode 4 is provided.
As the cathode, various kinds of cathodes including known organic EL cathodes can be used. For example, there are a magnesium-aluminum alloy, a magnesium-silver alloy, a magnesium-indium alloy, an aluminum-lithium alloy, and aluminum.

In the present invention, an electron transport layer 7 can be provided between the light emitting layer 3 and the cathode 4 as needed.
As the electron transporting substance, a substance having a high electron affinity and a high electron mobility is required, and a substance satisfying such conditions is a cyclopentadiene derivative (Japanese Patent Laid-Open Publication No.
289675), an oxadiazole derivative (Japanese Patent Application Laid-Open No. 2-216793), a bisstyrylbenzene derivative (Japanese Patent Application Laid-Open No. 1-245087), a p-phenylene compound (Japanese Patent Application Laid-Open No. 3-33183), a phenanthroline derivative ( JP-A-5-331459) and triazole derivatives (JP-A-7-90260).

These layers may be formed of a plurality of layers as long as the layers function as an organic EL element, or another layer may be interposed between the layers.

In the present invention, the interface layer 8 is provided between the light emitting layer 3 or the electron transporting layer 7 and the cathode 4, so that the driving voltage can be reduced, the luminous efficiency can be improved, and the life can be extended. Such an interface layer has the effect of facilitating electron injection from the cathode and the effect of increasing the adhesion to the cathode.

Examples of such an interface layer material include an alkali metal fluoride represented by lithium fluoride (Appl. Phys. Lett., 70, 152 (1997)), an alkaline earth metal fluoride, magnesium oxide, and oxide. There are oxides such as strontium, aluminum oxide, and barium oxide. Since such an interface layer material is itself an insulator, the film thickness used is usually 5 nm or less, and preferably 2 nm or less, and it is considered that tunnel injection from the cathode becomes possible.

In the organic EL device of the present invention, in order to secure storage stability and driving stability in the atmosphere, a polymer film is coated or sealed with glass to shut off from oxygen and moisture in the atmosphere. Good.

The organic EL device of the present invention is used as a full-surface light emitter, used as a backlight or a wall illumination device of a liquid crystal display device, or formed by patterning pixels.
It can be used as a display.

[0048]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not necessarily limited to these.

Example 1 (Example) An anode 2 (sheet resistance 7Ω / □) was formed on a glass substrate by depositing ITO to a thickness of 200 nm. On the anode 2, copper phthalocyanine (formula 2) was deposited to a thickness of 15 nm by a vacuum deposition method to form an interface layer 6. Then TP
D (Formula 3) was deposited to a thickness of 45 nm to form a hole transport layer 5.

Next, an aluminum complex of 8-oxyquinoline, Alq (formula 4) and 9,10-diphenoxyanthracene (formula 5) were co-deposited with a different deposition boat to a thickness of 60 nm to form a light emitting layer. did. At this time, the concentration of 9,10-diphenoxyanthracene was 5 mol.
% (Alq was 95 mol%). Finally, Mg and Ag are co-deposited to form a 200 nm-thick MgAg (10:
1) A cathode alloy was formed to produce an organic EL device.

[0051]

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[0052]

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[0053]

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[0054]

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Example 2 (Comparative Example) The light emitting layer of Example 1 was made only of Alq (formula 4) (9, 10-
Example 1 except that diphenoxyanthracene is not used)
In the same manner as in the above, an organic EL device using Alq as an organic light emitting layer was produced.

Example 3 (Example) On the anode 2 used in Example 1, MTDATA (formula 6) was deposited to a film thickness of 50 nm to form an interface layer 6. Then TP
D (Formula 3) was deposited to a thickness of 10 nm to form a hole transport layer 5. Then tetraphenylbutadiene (Formula 7) and 9,
10-bis (phenylethynyl) anthracene (formula 8)
Were co-evaporated with a different evaporation boat to a film thickness of 60 nm to form a light emitting layer.

At this time, the concentration of 9,10-bis (phenylethynyl) anthracene was 5 mol% (95 mol% of tetraphenylbutadiene). Finally, Mg
And Ag are co-deposited to form a 200 nm-thick MgAg (10:
1) A cathode alloy was formed to produce an organic EL device.

[0058]

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[0059]

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[0060]

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Example 4 (Example) On the anode 2 used in Example 1, a solution prepared by dissolving 1 part by weight of polyvinyl carbazole (formula 9) and 1 part by weight of TPD (formula 3) in 500 parts by weight of dichloromethane was used. Rotation speed 500
This substrate was spin-coated at a thickness of 60 nm at 0 rpm to form a hole transport layer. Then, bis (2-methyl-8-quinolinolato) (phenolate) aluminum (III) (formula 1)
0) and 9,10-bis (phenylthio) anthracene (Formula 11) using a different evaporation boat to a film thickness of 40 nm.
To form a light emitting layer.

At this time, the concentration of 9,10-bis (phenylthio) anthracene was 7 mol% (bis (2-methyl-8-quinolinolato) (phenolate) aluminum (III) was 93 mol%). Next, an organic layer consisting of bis (2-methyl-8-quinolinolato) (phenolate) aluminum (III) alone was used as an electron transport layer.
0 nm was formed. Finally, Mg and Ag were co-deposited to form a 200-nm-thick MgAg (10: 1) cathode alloy, to fabricate an organic EL device.

[0063]

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[0064]

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[0065]

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Example 5 (Example) On the anode 2 used in Example 1, MTDATA (formula 6) was deposited to a thickness of 50 nm to form an interface layer 6. Then, α-
NPD (Formula 12) and 5,12-diphenoxynaphthacene (Formula 13) were formed to a film thickness of 10 nm using different evaporation boats.
To form a hole transport layer.

At this time, the concentration of 5,12-diphenoxynaphthacene in the hole transporting layer was 8 mol% (α-
NPD is 92 mol%). Then, Alq (Equation 4) is changed to 60
A light emitting layer was formed by vapor deposition. Further, 0.5 nm of lithium fluoride was deposited to form an interface layer. Finally, A
to form a cathode having a thickness of 200 nm to form an organic EL.
An element was manufactured.

[0068]

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[0069]

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Example 6 (Example) On the anode 2 used in Example 1, MTDATA (formula 6) was deposited to a thickness of 50 nm to form an interface layer 6. Then, α-
NPD (Formula 12) was deposited to a thickness of 10 nm to form a hole transport layer 5. Next, Alq (Formula 4) and 5,12-diphenoxynaphthacene (Formula 13) were co-evaporated to a thickness of 40 nm using different evaporation boats to form a light emitting layer.

At this time, the concentration of 5,12-diphenoxynaphthacene was 8 mol% (Alq was 92 mol%).
%). Next, an organic layer consisting of only Alq was formed to a thickness of 20 nm as an electron transport layer. Further, 0.5 nm of lithium fluoride was deposited to form an interface layer. Finally, Al was vapor-deposited to form a cathode having a thickness of 200 nm, thereby producing an organic EL device.

The luminous efficiency characteristics (the luminance (c at the time of applying 10 V) of the organic EL elements produced in the above-described examples (Examples and Comparative Examples)
d / m ² ) and luminous efficiency (lm / W) are shown in Table 1.
The numbers in the columns of the light emitting layer and the hole transport layer indicate the formula numbers of the compounds.

The driving stability (10 mA / c in nitrogen)
initial luminance when driven at a constant current of m ² is the time required for a drop to half of the original half-life time (hours))
Table 2 shows the measurement results of the luminous efficiency (lm / W) after the luminance was reduced by half.

[0074]

[Table 1]

[0075]

[Table 2]

[0076]

As described above, according to the present invention,
A specific organic fluorescent material is contained in the light emitting layer and the hole transport layer. This facilitates energy transfer from excitons generated in the light emitting layer, and provides an organic EL device having high luminous efficiency and excellent life. The present invention is also applicable to various applications within a range that does not impair the effects of the present invention.

[Brief description of the drawings]

FIG. 1 is a side view of a basic example of an organic EL device of the present invention.

FIG. 2 is a side view of a preferred example of the organic EL device of the present invention.

[Explanation of symbols]

 1: substrate 2: anode 3: emission layer 4: cathode 5: hole transport layer 6: interface layer 7: electron transport layer 8: interface layer

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Irizawa 1150 Hazawacho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Asahi Glass Co., Ltd. (reference) 3K007 AB03 AB06 AB11 AB15 CB01 DA01 DB03 EB00 EC00 FA01

Claims (3)

[Claims] 1. An organic electroluminescent device having at least an anode, a light emitting layer containing an organic light emitting substance, and a cathode, wherein the light emitting layer contains a compound represented by the following general formula (1). Luminescent element. Embedded image (In the above formula, R ^{1 and} R ² each independently represent hydrogen, a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic hydrocarbon. X ¹ and X ² each independently represent an oxygen atom, a sulfur atom, a selenium atom, a tellurium atom, an ethynyl group, and m and n represent 1 or 2 Each of the hydrogen atoms of the aromatic condensed ring represented by m and n is a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic group. May be substituted with an aromatic hydrocarbon group, a phenylethynyl group, or an aromatic heterocyclic group.) 2. The organic compound according to claim 1, wherein a hole transport layer is provided between the anode and the light emitting layer containing an organic light emitting substance, wherein the hole transport layer contains the compound represented by the general formula (1). Electroluminescence element. 3. The compound represented by the general formula (1) is selected from the group consisting of X ¹ and X ²
Each independently represents an oxygen atom, a sulfur atom, or an ethynyl group, m + n represents 2 or 3, and a part of the hydrogen atoms of the aromatic condensed ring defined by m and n is an aryl group,
3. The organic electroluminescent device according to claim 1, wherein the compound is a compound represented by the formula: which may be substituted with an aryloxy group, an aromatic hydrocarbon group, or a phenylethynyl group.