JPH05310949A - Polyphosphzene compound - Google Patents

Abstract

PURPOSE:To provide the subject new compound having specific structure, useful as e.g. a positive hole carrying material for organic thin film electroluminescence elements or organic thin film photocells. CONSTITUTION:The objective compound having structure of formula I (n is an integer; R1 and R2 are each aromatic group, tertiary amine-contg. group or alkyl), e.g. a compound of formula II (R is H, methyl or trifluoromethyl). The compound of the formula I can be obtained by the following process: an aromatic tertiary amine's phenolic modification such as hydroxytriphenylamine and a dioxane such as 1,1,1-trifluoroethanol are dripped into a benzene solution of polydichlorophosphazene in the presence of an alkali such as sodium hydride, and the resulting salt is separated by filtration and reprecipitated in methanol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel polyphosphazene compound suitable as a hole transport material for an organic thin film EL (electroluminescence) device or an organic thin film photocell, or as a carrier transport material for electrophotography. Is.

[0002]

2. Description of the Related Art C. of Eastman Kodak Company. W. T
The organic thin film EL device developed by ang et al.
-194393, JP-A-63-264692, JP-A-63-295695, Applied Physics Letter Vol. 51 No. 12, page 913 (19)
1987), and Journal of Applied Physics, Vol. 65, No. 9, page 3610 (1989), etc., generally comprising an anode, an organic hole transport layer, an electron transport light emitting layer, and a cathode in this order. , Is made as follows.

First, an anode of a transparent conductive film of a complex oxide of indium and tin (hereinafter referred to as ITO) is formed on a transparent insulating substrate such as glass or a resin film by a vapor deposition method or a sputtering method. Next, copper phthalocyanine as an organic hole transport layer, or a compound represented by the following chemical formula:

[0004]

[Chemical 5]

1,1-bis (4-di-p-tolylaminophenyl) cyclohexane (melting point 181.4 ° C.-18
2.4 ° C.) or a compound represented by the following (Chemical Formula 6):

[0006]

[Chemical 6]

N, N, N ', N'-tetra-p-tolyl-1,1'-biphenyl-4,4'-diamine (melting point 1
20 ° C.) tetraaryldiamine or the like having a thickness of about 0.1 μm or less is formed in a single layer or by stacking and vapor deposition.

Next, an organic phosphor such as tris (8-quinolinol) aluminum is formed on the organic hole transport layer in an amount of 0.1 μm.
The organic electron transporting light emitting layer is formed by vapor deposition with a thickness of about the same or less. Finally, Mg: Ag, Ag: E as a cathode thereon.
Alloys of u, Mg: Cu, Mg: In, Mg: Sn, etc. are vapor-deposited by about 2000 Å.

According to the Applied Physics Letter Vol. 57, No. 6, page 531 (1990),
Adachi et al. Produced an element in which an organic electron transporting light emitting layer was divided into an organic light emitting layer and an organic electron injecting and transporting layer by laminating two kinds of materials. This device comprises N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-as an organic hole transport layer on an ITO anode.
4,4′-diamine (melting point 159 to 163 ° C.), 1- [4-N, N-bis (p-methoxyphenyl) aminostyryl] naphthalene as an organic light emitting layer, and 2- (4- Biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole (hereinafter, simply referred to as BPBD) and an alloy of Mg and Ag as a cathode are sequentially stacked.

However, in the organic hole transporting material shown above, copper phthalocyanine is heat-resistant but has a large absorption in the visible light wavelength region, and since it is crystalline, the vapor-deposited film becomes uneven and the element is electrically short-circuited. There was a problem that it became easier to do. Further, phthalocyanines are hardly soluble in organic solvents, and it was difficult to form a smooth thin film having a film thickness of 0.1 μm or less by a coating method using a solvent such as a spin coating method. The compounds represented by (Chemical Formula 5) and (Chemical Formula 6) are amorphous and have a smooth vapor-deposited film, and have no absorption in the visible light wavelength region, but have a low melting point.
There is a problem that the element is easily melted due to heat generated during the element manufacturing process and element driving. Further, since it is a low molecular weight compound, the strength of the film is considered to be weak.

As described above, the following four points are required as properties of the material of the hole transport layer of the organic thin film EL element. 1. Must be colorless and transparent in the visible light range. 2. It is possible to form a smooth film having a film thickness of 0.1 μm or less without pinholes at a low cost by a coating method using a solvent such as a spin coating method. 3. Capable of imparting high heat resistance of 200 ° C or higher. 4. Large hole transport capability. In the present invention, a hole transport material for an organic thin film EL device, a hole transport material for an organic thin film photovoltaic cell, which has high heat resistance and is suitable for a film forming method using a solvent, which solves the above problems, is used for electrophotography. The purpose of the present invention is to provide a novel polyphosphazene compound that can be applied to a carrier transport material.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is composed of polyphosphazene, which is colorless and transparent and has a high molecular weight and good film-forming property, as a main chain and a side chain. It is a novel polyphosphazene compound represented by the general formula (Formula 1) obtained by substituting a carrier-transporting group. The polyphosphazene compound according to the present invention is, for example, a compound represented by the general formula (Formula 2), which is colorless and transparent in the visible region, can form an amorphous and smooth film, and has a high hole mobility. Aromatic tertiary amines such as phenylamine are introduced into the side chains so that hole and electron carriers can be transported by hopping conduction of holes and electrons between the side chains.

Further, as shown in the general formula (Formula 3), --O-(CH ₂ ) ₂ --O is provided between the triphenylamine and the main chain.
It is also possible to introduce chains to increase the flexibility of the side chains.
Further, as shown in the general formula (Formula 4), a CF ₃ CH ₂ — group,
Or CH ₃ — group, CH ₃ CH ₂ — group, C ₃ F ₇ CH ₂
The flexibility of the molecule can be increased by partially introducing an alkyl group such as a -group.

The polyphosphazene of the present invention is synthesized by dissolving a solution of polydichlorophosphazene in benzene, tetrahydrofuran or the like in the presence of an alkali such as sodium hydride to give hydroxytriphenylamine or (N, N'-diphenylamino). Phenols and alcohols of aromatic tertiary amines such as phenoxy-2-ethanol and 1,
It is carried out by adding dropwise to an ether solution of an alcohol such as dioxane for introducing an alkyl group such as 1,1-trifluoroethanol, filtering off a salt formed, and then reprecipitating the polymer from methanol or the like.

As other aromatic tertiary amines, trinaphthylamine, tetraphenylbenzidine monohydroxy-substituted compounds and the like can be similarly reacted with polydichlorophosphazene and introduced into the main chain of polyphosphazene. .. Further, when the polyphosphazene of the present invention is formed into a film and used as a carrier transport layer such as a hole transport layer, adjacent electrodes having different work functions or other adjacent carrier transport layers having different work functions or light emitting layer materials In order to smoothly transfer electrons and holes through the highest occupied molecular orbital to the molecule, it is necessary to arrange the work function levels of adjacent layers in a stepwise manner. Therefore, using ditolylamine instead of diphenylamine as a synthetic raw material, introducing two methyl groups on the triphenylamine skeleton, increasing the electron density on nitrogen and decreasing the work function by 0.1 to 0.2 eV, and the like. It is also possible to introduce a trifluoromethyl group using bis (trifluoromethylphenyl) amine to reduce the electron density on nitrogen and adjust the work function to a large value of 0.1 to 0.2 eV.

The polyphosphazene thus obtained is dissolved in an organic solvent and then IT is formed by a method such as spin coating.
By coating on an electrode such as O, it functions as a hole transport layer of the organic thin film EL element. When the polyphosphazene compound of the present invention is used as a carrier transport material in a function-separated photoreceptor in electrophotography,
Organic dyes such as perylene-based, polycyclic quinone-based, phthalocyanine-based, and azo-based dyes described as organic carrier-generating materials on page 441 of "Basics and Applications of Electrophotographic Technology" published by Corona Publishing Co., Ltd., Electrophotographic Society. Se, Se-Te, CdS,
A carrier transport layer can be formed by coating on a carrier generation layer containing an inorganic material such as amorphous Si.

[0017]

The polyphosphazene used as the main chain of the compound of the present invention is colorless and transparent, has a high molecular weight and thus has a good film-forming property, and has two carrier-transporting groups per repeating unit of -P = N-. Therefore, high carrier transport capability is provided. In addition, due to the high molecular weight, the heat resistance is higher than in the case of low molecular weight.

[0018]

【Example】

<Example 1> Synthesis of polybis (N, N-diphenylaminophenoxy) phosphazene 3-hydroxytriphenylamine obtained by Ullmann reaction of diphenylamine and 3-iodoanisole was ether-decomposed with chlorotrimethylsilane to obtain 3-hydroxy. After dissolving 35.9 g (138 mmol) of triphenylamine in a mixed solvent of tetrahydrofuran and dioxane and reacting with 3.3 g (138 mmol) of sodium hydride,
60 ml of a tetrahydrofuran solution containing 4 g (34.5 mmol) of polydichlorophosphazene was added dropwise, and the mixture was heated at 70 ° C. for 8 hours.
Reacted for hours. The obtained product was purified by reprecipitation from a tetrahydrofuran solution in methanol to obtain white polybis (N, N-diphenylaminophenoxy) phosphazene.

This polymer has a melting point of 250 ° C. or higher, and the ¹³ C-NMR spectrum of its CDCl ₃ solution is shown in FIG. The peak of the weight average molecular weight of this polymer was 430,000 (in terms of polystyrene) by GPC analysis.
The work function was about 5.8 eV as measured by AC-1 manufactured by Riken Keiki Co., Ltd. The UV / visible absorption spectrum of this polymer spin coat film is shown in FIG.
There is no absorption in the visible region above 00 nm.

[0020]

Example 2 Synthesis of polybis (3- (N, N-diphenylamino) phenoxy-2-ethoxy) phosphazene 3- (N, N-) obtained by reacting 3-hydroxytriphenylamine with 2-chloroethanol. Diphenylamino) phenoxy-2-ethanol was used in place of 3-hydroxytriphenylamine in Example 1 and the same reaction and purification were carried out to obtain white polybis (3- (N, N-diphenylamino) phenoxy-2- Ethoxy) phosphazene was obtained.

The polymer has a melting point above 250 ° C.,
The ¹³ C-NMR spectrum of the CDCl ₃ solution is shown in FIG. The work function was about 5.8 eV.

[0022]

Example 3 In the reaction of Example 2, 1,1,1-trifluoroethanol was added and the reaction and purification were carried out in the same manner. As a result, 3- (N, N-diphenylamino) phenoxy-2 was obtained.
-A white polymer was obtained in which 81% of ethanol and 19% of 1,1,1-trifluoroethanol were replaced.

The infrared absorption spectrum of this polymer measured by the KBr method is shown in FIG. The polymer softened at 150 ° C. or higher. The work function was about 5.9 eV.

[0024]

EFFECTS OF THE INVENTION According to the present invention, a film having a low melting point, crystallinity and smoothness like triphenylamine cannot be obtained, and since it has a low molecular weight and a low vapor pressure, it is re-evaporated from the substrate in a vacuum. Even in the case of a carrier-transporting substance that is difficult to form by vacuum evaporation, by synthesizing a hydroxy compound and introducing it as a side chain of polyphosphazene, a heat-resistant polymer that is soluble in an organic solvent can be obtained. As a result, a smooth and transparent polyphosphazene thin film can be obtained.
Since this film can contain a carrier transporting substance in a higher concentration than a film obtained by dispersing low molecules in a polymer binder, it is useful for an organic thin film EL device and an organic thin film photovoltaic cell, and is also useful for electrophotography. It also has excellent properties as a carrier transport material in the function-separated type photoreceptor.

[0025]

[Brief description of drawings]

FIG. 1 shows ¹³ C—N of the polyphosphazene compound of the present invention.
It is a graph which shows an MR spectrum.

FIG. 2 is a graph showing an ultraviolet-visible absorption spectrum of the polyphosphazene compound of the present invention.

FIG. 3: ¹³ C—N of the polyphosphazene compound of the present invention
It is a graph which shows an MR spectrum.

FIG. 4 is a graph showing an infrared absorption spectrum of the polyphosphazene compound of the present invention.

Claims (4)

[Claims] 1. A polyphosphazene compound represented by the following general formula (Formula 1). [Chemical 1] 2. A method represented by the following general formula (Formula 2):
The polyphosphazene compounds described. [Chemical 2] 3. A method represented by the following general formula (Formula 3):
The polyphosphazene compounds described. [Chemical 3] 4. A method represented by the following general formula (Formula 4):
The polyphosphazene compounds described. [Chemical 4]