JPH05125359A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To obtain the subject element suitable as display devices such as a planar light source as a back light or a flat panel display due to its excellent uniformity, stability, etc., of light emission by forming a luminous layer containing an aromatic compound having a specific structure. CONSTITUTION:An organic electroluminescent element having a luminous layer containing an aromatic compound expressed by formula I [A1 to A4 are formula II or III (R<1> to R<6> are H, 1-12C alkyl, etc.), etc.] between a pair of electrodes in which at least either is (semi)transparent. 1,2,4,5-Tetrakis(phenylethyl)benzene, etc., are preferred as the compound expressed by formula I, which is obtained by reacting, e.g. 1,2,4,5-tetrakis(bromomethyl)benzene with triphenylphosphine, providing a phosphonium salt and then reacting the resultant phosphonium salt with an aldehyde. The luminous layer is preferably formed by a vacuum vapor deposition method.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an organic electroluminescence device (hereinafter referred to as an organic EL device). For more information,
The present invention relates to an organic EL device using a benzene derivative having four vinylene groups as a light emitting material.

[0002]

2. Description of the Related Art Inorganic electroluminescence device (hereinafter, inorganic EL device) using an inorganic phosphor as a light emitting material
Is used for a surface light source as a backlight or a display device such as a flat panel display, for example, but a high-voltage alternating current was required to emit light.

Recently, Tang et al. Have an organic EL having a two-layer structure in which an organic fluorescent dye is used as a light emitting layer and an organic hole transporting compound used in a photoconductor for electrophotography is laminated.
Fabricate the element, low voltage drive, high efficiency, high brightness organic EL
A device was realized (Japanese Patent Laid-Open No. 59-194393). Compared with inorganic EL elements, organic EL elements are characterized by low voltage driving, high brightness, and the ability to easily obtain light emission of many colors. Therefore, many organic EL elements have a large number of elements, organic fluorescent dyes, and organic charge transport compounds. Attempts have been reported [Japanese Journal of Applied Physics (Jpn.J.Appl.Phys.) Vol. 27, L269 (1988).
)], [Journal of Applied Physics (J. Appl. Phys.) Vol. 65, page 3610 (1989)].

[0004]

The organic EL devices reported so far have high brightness, but have the problem that the life of the light emitting device is short. It is said that the cause is that the structure of the light emitting layer is changed due to heat generation of the element and deteriorates. Therefore, a light emitting material that constitutes a thermally stable light emitting layer has been demanded.

[0005]

Means for Solving the Problems The present inventors
As a result of diligent study on the light emitting material of the device, as a light emitting compound, among the aromatic vinylene compounds having a benzene ring as a skeleton, a compound containing four vinylene groups is used to form a uniform light emitting layer, The inventors have found that an organic EL device that emits light uniformly can be obtained, and completed the present invention.
That is, the present invention provides an organic electroluminescence device having at least a light emitting layer between a pair of electrodes, at least one of which is transparent or semitransparent, wherein the light emitting layer is

[0006]

[Chemical 4] [In the formula, A ₁ , A ₂ , A ₃ and A ₄ each independently represent a group selected from the following formulas 5 and 6.

[0007]

[Chemical 5] as well as

[0008]

[Chemical 6] (R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ ,
R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , and R ₁₄ are each independently hydrogen, an alkyl group or an alkoxy group having 1 to 12 carbon atoms, an aryl group or an aryloxy group having 6 to 14 carbon atoms, or a nitro group. , Means a group represented by a heterocyclic compound group. )]] The organic electroluminescent element characterized by containing at least 1 sort (s) of aromatic compound selected from the compound represented by these. Less than,
The organic EL element of the present invention will be described in detail.

The light emitting material used in the present invention is the aromatic compound represented by the above chemical formula 4, wherein A ₁ , A ₂ ,
As described above, A ₃ and A ₄ are a phenyl group, a naphthyl group,
Anthryl group, pyridyl group, thienyl group, or a derivative in which an alkyl or alkoxy group having 1 to 12 carbon atoms, an aryl or aryloxy group having 6 to 14 carbon atoms, a nitro group or a heterocyclic compound group is nuclear-substituted. .. Among these, a phenyl group, a pyridyl group and their derivatives, which have good film-forming properties, are preferable. Here, as the alkyl group having 1 to 12 carbon atoms, for example, methyl, ethyl, butyl, octyl and the like are preferable, and methyl and ethyl are preferable. Alternatively, the alkoxy group having 1 to 12 carbon atoms includes methoxy, ethoxy, butoxy, heptyloxy and the like, and methoxy and ethoxy are preferable. The aryl group is a phenyl group, 4-methylphenyl group, 4-ethylphenyl group, 4-propylphenyl group, 4-butylphenyl group, 4-pentylphenyl group, 4-hexylphenyl group, 1-naphthalene group, 2- Examples of the naphthalene group and the aryloxy group include 4-methoxyphenyl group, 4-ethoxyphenyl group, 4-propoxyphenyl group, 4-butoxyphenyl group, 4-pentyloxyphenyl group, 4-hexyloxyphenyl group, and phenoxy group. To be done. Examples of the heterocyclic compound group include a thienyl group, a pyridin-2-yl group, a pyridin-3-yl group and a pyridin-4-yl group.

Specific compounds include 1,2,4,5-tetrakis (phenylethynyl) benzene, 1,2,4, and
5-tetrakis (2'-pyridylethynyl) benzene,
1,2,4,5-tetrakis (p-methoxyphenylethynyl) benzene, 1,2,4,5-tetrakis (2,2
5-dimethoxyphenylethynyl) benzene, 1,2,
4,5-tetrakis (naphthylethynyl) benzene,
1,2,4,5-tetrakis (anthranylethynyl)
Examples thereof include benzene, 1,2,4,5-tetrakis (thienylethynyl) benzene, and 1,2,4,5-
Tetrakis (phenylethynyl) benzene, 1,2,
4,5-Tetrakis (p-methoxyphenylethynyl)
Benzene and 1,2,4,5-tetrakis (2,5-dimethoxyphenylethynyl) benzene are preferable from the viewpoint of fluorescence intensity and film forming property.

The aromatic compound represented by the above chemical formula 4 is a benzene derivative, and the synthesis method is not particularly limited, but it is common to use a reaction for forming a carbon-carbon double bond, and the Wittig reaction, Examples thereof include a sulfonium salt decomposition method and a dehydrohalogenation method. Specifically, for example, 1,2,4,5-tetrakis (bromomethyl) benzene is reacted with triphenylphosphine to form a phosphonium salt, and then aldehyde corresponding thereto is reacted (Wittig reaction) to synthesize. Further, when these compounds are used as a light emitting layer of an organic EL device, it is desirable to carry out purification such as reprecipitation purification, sublimation purification and the like after the synthesis because the purity affects the light emitting characteristics.

The light emitting layer containing the aromatic compound represented by the above chemical formula 4 is applied by a vacuum deposition method or a solution of the aromatic compound by a spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method or the like. It can be formed by a known method. In addition, when a thin film is formed by a coating method, in order to remove the solvent, under reduced pressure or in an inert atmosphere, 30 to 200 ° C., preferably 60 to
Heat treatment at a temperature of 100 ° C. is desirable. The vacuum vapor deposition method is preferably used from the viewpoint of finely controlling the film thickness.

The present invention also includes the use of a layer obtained by mixing the above aromatic compound and a known polymer compound as the light emitting layer. In this case, the polymer compound to be used is not particularly limited, but those which do not extremely disturb the charge transport property and the light emitting property are preferable, and examples thereof include poly (N-vinylcarbazole), polyaniline and its derivatives, polythiophene and its derivatives, and polythiophene. (P-phenylene vinylene) and its derivatives, poly (2,5-thienylene vinylene) and its derivatives, polycarbonate, polysiloxane, and vinyl polymers such as polymethyl acrylate, polymethyl methacrylate, polystyrene and polyvinyl chloride. Is exemplified. In addition, here, poly (N-
Vinylcarbazole), polyaniline and its derivatives,
Polythiophene and its derivative, poly (p-phenylene vinylene) and its derivative, poly (2,5-thienylene vinylene) and its derivative also have the action as a charge transporting compound mentioned below.

The formation of the mixed layer of the aromatic compound and the polymer compound is carried out by mixing the polymer compound and the aromatic compound in a solution state or a molten state, dispersing the aromatic compound, and then applying the above-mentioned coating. You can use the law. In this case, the amount of the aromatic compound dispersed in the polymer is not particularly limited, but is usually 1 to 100 relative to 100 parts by weight of the polymer compound.
Parts by weight, preferably 20 to 70 parts by weight.

When a precursor polymer such as poly (p-phenylene vinylene) and its derivative and poly (2,5-thienylene vinylene) and its derivative is used, after mixing with the aromatic amine compound in a solution state, Under active atmosphere,
Heat treatment is performed at a temperature of 30 to 200 ° C., preferably 60 to 100 ° C. to convert the polymer into a target polymer.

In the present invention, a charge transport layer is provided between the light emitting layer and any of the electrodes (the charge transport layer in the present invention is a generic term for a hole transport layer and an electron transport layer unless otherwise specified). It may be provided. There is no particular limitation on the charge transport material (general term for hole transport material and electron transport material) used at that time, and examples thereof include triphenyldiamine derivatives, oxadiazole derivatives, pyrazoline derivatives, arylamine derivatives, stilbene derivatives, and anthracenes. A quinodimethane derivative or the like can be used. In particular,
For example, JP-A-2-209988 and 3-3799.
Known materials such as those described in Japanese Patent Publication No. 2 can be used. Of these, either the electron-transporting compound or the hole-transporting compound, or both, may be used at the same time. The thickness of the charge transport layer varies depending on the type of compound used and the like, and therefore may be appropriately determined in consideration of those in a range that does not impair sufficient film formability and light emission characteristics.

These charge-transporting materials can be compounded by known methods such as vacuum deposition, or coating methods such as spin-coating, casting, dipping, bar-coating and roll-coating methods of the solution of the charge-transporting material. The charge transport layer can be formed by appropriately adopting it. When the charge transport material is not a polymer compound, it is preferable to use the vacuum vapor deposition method from the viewpoint of finely controlling the film thickness.

In the present invention, further as a light emitting layer,
A mixture of the aromatic compound as the light emitting material and the charge transport material may be used, or a mixture of these may be used as a layer in which a known polymer compound is used as a medium and dispersed therein. .. The mixing ratio of the light emitting material and the charge transport material is not particularly limited, but is preferably 0.1:
It is in the range of 100 to 1: 1 (weight), and the ratio of the sum of the polymer compound and these materials is not particularly limited, but is preferably in the range of 100: 0.01 to 1: 3 (weight).
In this case, the polymer compound used is preferably the above-mentioned polymer compound which does not strongly absorb visible light. Specifically, poly (N-vinylcarbazole), polythiophene and its derivatives, poly (p-phenylene vinylene) and its derivatives, poly (2,5-thienylene vinylene) and its derivatives, polycarbonate, polymethyl acrylate, polymethyl Examples thereof include methacrylate, polystyrene, polyvinyl chloride, polysiloxane and the like. The same method as described above can be used to form the mixed layer. Further, although these layers can be used in only one layer, another layer of a charge transport material or the like may be provided if necessary.

The structure of the organic EL device of the present invention will be described below. The structure itself of the element can be a known structure. For example, the above-mentioned anode / charge (hole) transport layer / light-emitting layer / cathode (/ indicates that the layers are stacked), or anode / charge (hole or electron) transport / light-emission (charge transport material and Other than the structure of the luminescent material and the mixture) layer / cathode,
It is possible to have a combination structure having a conductive polymer layer between the anode and the charge (hole) transport layer, or a combination structure having a charge (electron) transport layer between the light emitting layer and the cathode. It can also be taken. Furthermore, anode / conductive polymer /
A structure of charge (hole) transporting layer / light emitting layer / charge (electron) transporting layer / cathode can also be adopted.

Hereinafter, regarding the production of the organic EL device, the anode /
The production method will be described below by taking an example of a structure of charge (hole) transport layer / light emitting layer / cathode. Transparent of a pair of electrodes,
Alternatively, as the semitransparent electrode, a transparent or semitransparent electrode is formed on a transparent substrate such as glass or transparent plastic.
This is the anode. A conductive metal oxide film, a semitransparent metal thin film, or the like is used as the material of the electrode. Specifically, indium tin oxide (ITO), tin oxide (NESA), Au, Pt, Ag, Cu or the like is used. As a manufacturing method, a vacuum deposition method, a sputtering method, a plating method, or the like is used.

Next, the charge transport layer is provided, and the film thickness is 5Å to 10 μm, preferably 10Å to 1 μm. 20 to increase the current density and the emission brightness
The range of up to 5000 Å is preferred.

Next, a light emitting layer is provided on the charge transport layer.
The film thickness of the light emitting layer needs to be at least such that pinholes are not generated, but if it is too thick, the resistance of the device increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of the light emitting layer is 5Å to 10 μm, preferably 10
Å-1 μm, more preferably 50-2000 Å. Note that this range is also preferable in the case of a mixed layer of a charge transport material and a light emitting material.

Next, an electrode is provided on the light emitting layer. This electrode becomes the electron injection cathode. The material is not particularly limited, but a material having low ionization energy is preferable. For example, Al, In, Mg, Mg-Ag alloy, M
A g-In alloy, a graphite thin film, etc. are used. As a method for producing the cathode, a known vacuum deposition method, sputtering method or the like is used.

Although the organic EL device of the present invention can be manufactured as described above, it is possible to manufacture the organic EL device having another structure by the same method.

[0025]

The benzene derivative having four vinylene groups used as a light emitting material in the present invention has a π-conjugated system extending to four vinylene groups, and even if one or two of them are modified by some cause. It is considered that the molecule is thermally stable because it has the ability as a light emitting material and has a relatively high melting point and decomposition temperature.

[0026]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

Reference Example 1 (Synthesis of 1,2,4,5-tetrakis (p-methoxyphenylethynyl) benzene) 1,2,4,5-tetrakis (bromomethyl) benzene and triphenylphosphine were added to N, N-dimethyl. 150 in formamide (DMF)
The reaction was carried out at ℃ for 3 hours. Cool the reaction to room temperature,
The formed precipitate was filtered, washed with DMF, and dried under reduced pressure to obtain a phosphonium salt. This phosphonium salt and p
-Methoxybenzaldehyde and ethanol were dissolved, and an ethanol solution of lithium ethoxide was added dropwise at room temperature. After dropping, stir for an additional 1 hour to react (Wittig)
Let The precipitate formed is filtered, ethanol,
It was washed with ethanol / water and ethanol and then dried under reduced pressure to obtain 1,2,4,5-tetrakis (p-methoxyphenylethynyl) benzene.

Reference Example 2 (Synthesis of 1,2,4,5-tetrakis (phenylethynyl) benzene) 1 was prepared in the same manner as in Reference Example 1 except that benzaldehyde was used instead of p-methoxybenzaldehyde. , 2,4,5-Tetrakis (phenylethynyl) benzene was synthesized.

Reference Example 3 (Synthesis of 1,2,4,5-tetrakis (2,5-dimethoxyphenylethynyl) benzene) Other than carrying out the reaction using 2,5-dimethoxybenzaldehyde instead of p-methoxybenzaldehyde. Produced 1,2,4,5-tetrakis (2,5-dimethoxyphenylethynyl) benzene in the same manner as in Reference Example 1.

Example 1 4,4'-bis (3-methyl-diphenylamino) biphenyl (hereinafter TPD) was used as a charge (hole) transport layer on a glass substrate having an ITO film with a thickness of 200Å formed by sputtering 3 ×. 1 by vapor deposition under vacuum of 10 ^-6 Torr
A film was formed with a thickness of 000Å. Then, 1,2,4,5-tetrakis (p-methoxyphenylethynyl) benzene synthesized in Reference Example 1 was used as a light emitting layer thereon to form 600
Å, and indium was further deposited thereon as a cathode by 6000Å to prepare an organic EL device. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 20 V was applied to this element, the current density was 16.8 mA / c
A current of m ² was flowed, and bluish white uniform EL light emission with a brightness of 0.011 cd / m ² was observed. The brightness was proportional to the current density.

Example 2 An ITO film was attached to a thickness of 200 Å by sputtering.
4,4'-bilayer as a charge (hole) transport layer on a glass substrate.
Sus (3-methyl-diphenylamino) biphenyl (hereinafter
TPD) 3 x 10^-61 by vapor deposition under a vacuum of Torr
A film was formed with a thickness of 000Å. Then a light emitting layer on top of it
1,2,4,5-tetrakis synthesized in Reference Example 2
(Phenylethynyl) benzene 1000Å,
6000Å vapor deposition of indium as cathode on top of organic E
An L element was produced. The degree of vacuum during vapor deposition is 3 x 1
0^-6It was below Torr. Apply a voltage of 18V to this device.
When added, the current density is 156 mA / cm²Current flows
Brightness 0.692 cd / m ²Blue-white uniform EL emission
Light was observed. The brightness was proportional to the current density.

Example 3 A glass substrate having an ITO film with a thickness of 200 Å formed by sputtering was spin-coated with 0.1% N-methylpyrrolidone solution of polyaniline to give 200 Å charges (holes). A transport layer was prepared. Then, 1, 2,
An organic EL device was produced by depositing 4,5-tetrakis (2,5-dimethoxyphenylethynyl) benzene at 1000 Å and further depositing indium as a cathode at 6000 Å thereon. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 16 V was applied to this element,
A current with a current density of 119 mA / cm ² flows and the brightness is 3 cd
A uniform bluish white EL emission of / m ² was observed. The brightness was proportional to the current density.

[0033]

The organic EL element using the light emitting material of the present invention exhibits excellent light emitting characteristics such as uniformity of light emission and stability, and is suitable for a planar light source as a backlight and a display device such as a flat panel display. Can be used for.

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[Procedure amendment]

[Submission date] December 20, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010] Specific compounds 1,2,4,5-tetrakis (Fenirue Te) benzene, 1,2,4,
5- tetrakis (2'Pirijirue Te) benzene,
1,2,4,5-tetrakis (p-methoxyphenylene
Te) benzene, 1,2,4,5-tetrakis (2,
5-dimethoxyphenyl d Te) benzene, 1,2,
4,5-tetrakis (Nafuchirue Te) benzene,
1,2,4,5-tetrakis (Antoranirue Te nil)
Benzene, 1,2,4,5-tetrakis (Chienirue Te <br/> sulfonyl) the like benzene, 1,2,4,5
Tetrakis (Fenirue Te) benzene, 1,2,
4,5-tetrakis (p- methoxyphenyl d Te sulfonyl)
Benzene, 1,2,4,5-tetrakis (2,5-dimethoxyphenyl d Te) benzene fluorescence intensity, from the viewpoint of film forming property.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

[0027] Reference Example 1 (1,2,4,5-tetrakis (p- Synthesis methoxyphenyl d Te) benzene) 1,2,4,5 tetrakis (bromomethyl) benzene and triphenylphosphine N, N 150 in dimethylformamide (DMF)
The reaction was carried out at ℃ for 3 hours. Cool the reaction to room temperature,
The formed precipitate was filtered, washed with DMF, and dried under reduced pressure to obtain a phosphonium salt. This phosphonium salt and p
-Methoxybenzaldehyde and ethanol were dissolved, and an ethanol solution of lithium ethoxide was added dropwise at room temperature. After dropping, stir for an additional 1 hour to react (Wittig reaction
I did it. The resulting precipitate was filtered, successively ethanol, washed with ethanol / water ,, ethanol, dried under reduced pressure to 1,2,4,5-tetrakis (p- methoxyphenyl d Te sulfonyl) give benzene.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

[0028] In Reference Example 2 (1,2,4,5-tetrakis (Fenirue Te yl) Synthesis of benzene) p-methoxybenzaldehyde, except that the reaction was carried out using benzaldehyde in place of Reference Example 1 and the same methods 1,2,4,5-tetrakis (Fenirue Te nil) was synthesized benzene.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029] A reaction is conducted by using Reference Example 3 (1,2,4,5-tetrakis (2,5-dimethoxyphenyl d Te yl) Synthesis of benzene) p-2,5-dimethoxybenzaldehyde instead of methoxybenzaldehyde other than the was synthesized 1,2,4,5-tetrakis (2,5-dimethoxyphenyl d Te) benzene in the same manner as in reference example 1.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

Example 1 4,4'-bis (3-methyl-diphenylamino) biphenyl (hereinafter TPD) was used as a charge (hole) transport layer on a glass substrate having an ITO film with a thickness of 200Å formed by sputtering 3 ×. 1 by vapor deposition under vacuum of 10 ^-6 Torr
A film was formed with a thickness of 000Å. Then the upper synthesized in Reference Example 1 as a light-emitting layer 1,2,4,5-tetrakis (p- methoxyphenyl d Te) benzene 600
Å, and indium was further deposited thereon as a cathode by 6000Å to prepare an organic EL device. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 20 V was applied to this element, the current density was 16.8 mA / c
A current of m ² was flowed, and bluish white uniform EL light emission with a brightness of 0.011 cd / m ² was observed. The brightness was proportional to the current density.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

Example 2 An ITO film was attached to a thickness of 200 Å by sputtering.
4,4'-bilayer as a charge (hole) transport layer on a glass substrate.
Sus (3-methyl-diphenylamino) biphenyl (hereinafter
TPD) 3 x 10^-61 by vapor deposition under a vacuum of Torr
A film was formed with a thickness of 000Å. Then a light emitting layer on top of it
1,2,4,5-tetrakis synthesized in Reference Example 2
(PhenyleTeNil) benzene 1000 Å, then
6000Å vapor deposition of indium as cathode on top of organic E
An L element was produced. The degree of vacuum during vapor deposition is 3 x 1
0^-6It was below Torr. Apply a voltage of 18V to this device.
When added, the current density is 156 mA / cm²Current flows
Brightness 0.692 cd / m ²Blue-white uniform EL emission
Light was observed. The brightness was proportional to the current density.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

Example 3 A glass substrate having an ITO film with a thickness of 200 Å formed by sputtering was spin-coated with 0.1% N-methylpyrrolidone solution of polyaniline to give 200 Å charges (holes). A transport layer was prepared. Then, 1, 2,
4,5-tetrakis (2,5-dimethoxyphenyl et te <br/> sulfonyl) 1000 Å benzene, to produce an organic EL device was further 6000Å depositing indium as a cathode thereon. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 16 V was applied to this element,
A current with a current density of 119 mA / cm ² flows and the brightness is 3 cd
A uniform bluish white EL emission of / m ² was observed. The brightness was proportional to the current density.

Claims (1)

[Claims] 1. An organic electroluminescent device having at least a light emitting layer between a pair of electrodes, at least one of which is transparent or semitransparent, wherein the light emitting layer is represented by the following chemical formula 1. [In the formula, A ₁ , A ₂ , A ₃ and A ₄ each independently represent a group selected from the following chemical formulas 2 and 3. [Chemical 2] And (R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ ,
R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , and R ₁₄ are each independently hydrogen, an alkyl group or an alkoxy group having 1 to 12 carbon atoms, an aryl group or an aryloxy group having 6 to 14 carbon atoms, or a nitro group. , Means a group represented by a heterocyclic compound group. )] At least one aromatic compound selected from the compounds represented by the formula (1).