JP2016095453A - Electron transport material and electronic material using the electron transport material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron transport material which is excellent in compatibility with an organic solvent and a binder resin, has no risk of causing liquid sagging and cracks after having been applied to a support, has an electron transportation capability with excellent sensitivity, and enables synthesis which is extremely easy and inexpensive than a conventional one and has high yield; and an electronic material using the electron transport material.SOLUTION: An electron transport material contains an alanine derivative represented by Formula (I). In Formula (I), Rand Rare the same or different from each other, and represent an alkyl group having 6 to 16 carbon atoms. The alanine derivative is preferably synthesized by a reaction of naphthalene tetracarboxylic dianhydride and alanine alkyl ester or alanine.SELECTED DRAWING: None

Description

  The present invention relates to an electron transport material containing an alanine derivative that exhibits excellent electron transport ability and excellent solubility in an organic solvent, and an electronic material using the electron transport material.

  Naphthalene tetracarboxylic acid diimides represented by the following general formula (II) as described in Patent Document 1 (hereinafter sometimes referred to as “NTC”) are promising as electronic materials such as electron transport materials. Has been.

In general formula (II), R and R ′ are the same or different and each represents an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, or an alkoxy group.

The biggest drawback of the NTC (II) is that its solubility in an organic solvent is very poor. For example, a binder that forms a photosensitive layer when used as an electron transport material in an electrophotographic photosensitive member for a copying machine. The compatibility with the resin is low, and crystallization may occur in the photosensitive layer, or cracks may occur after application to the support and drying.
In order to solve such problems, attempts have been made so far to introduce various substituents into R and R ′ in the above formula (II).

For example, Patent Document 2 proposes a compound represented by the following general formula (III).
In this compound (III), two substituents R ₃ (contributing to imparting fat solubility, substituent R ₃ having high fat solubility) and R ₄ (contributing to imparting polarity) to the carbon bonded to the nitrogen atom, An ester group (COOR ₄ )) has been introduced.

In general formula (III),
R ₃ is an alkyl group having 2 to 12 carbon atoms, an alkyl group having 1 to 4 carbon atoms substituted with an ester group having an alkyl group having 1 to 4 carbon atoms, an aralkyl group having 7 to 15 carbon atoms, or carbon It is a C5-C8 cycloalkyl group, The said aralkyl group and cycloalkyl group may be substituted by the ester group which has a C1-C4 alkyl group.
R ₄ is an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or a cycloalkyl group having 3 to 10 carbon atoms, and the aryl group or aralkyl group And the cycloalkyl group may be substituted with an alkyl group having 1 to 6 carbon atoms.

However, although the compound (III) into which the two substituents R ₃ and R ₄ are introduced is excellent in solubility in tetrahydrofuran, the compound after introduction is difficult to crystallize, so the yield is low and the column It requires a purification (removal of impurities) step such as chromatography, and is inferior in practicality for industrial synthesis.
Depending on the number of carbon atoms in R _4, the compound has a low melting point. When the actually prepared coating solution is applied as a photosensitive layer to a drum-shaped support and then dried at a high temperature (about 100 ° C.), There is a possibility that (a phenomenon in which the coating liquid drips) may occur.

On the other hand, the applicant of the present application first developed a compound represented by the following general formula (IV), and attempted to increase the solubility in organic solvents by increasing the steric hindrance of the substituent. (See Patent Document 3).
However, the longer the two alkyl chains R ₅ and R ₆ are lengthened in order to increase the steric hindrance, the compound for introducing a substituent (an amine compound having alkyl groups R ₅ and R ₆ ). This makes it difficult to obtain and significantly increases the cost, which is a foothold for industrial scale synthesis.

In general formula (IV), R ₅ and R ₆ are the same or different and represent a linear or branched alkyl chain having 2 to 12 carbon atoms.

Thus, although NTCs into which various substituents have been introduced have been developed so far, the market always has better solubility and electron transport capability than those conventional products, and There is a demand for the development of an electron transport material that is simpler and has a higher yield than conventional products and can be industrially synthesized.
In addition, the presence of impurities hinders electron transfer and tends to cause deterioration of the electronic material. Therefore, the purity is preferably close to 100%.

Japanese Patent Publication No. 1-339098 Japanese Patent No. 5197417 Japanese Patent Application No. 2013-233714

  In consideration of the current situation as described above, the present inventors have excellent compatibility with organic solvents and binder resins, there is no risk of dripping or cracking after application to a support, and the electron transport ability has good sensitivity. And an electron transport material that is extremely easy and cheaper than conventional products and can be synthesized with high yield and purity, and an electronic material using such an electron transport material. To do.

In order to solve the above problems, the present inventors have conducted extensive studies,
α) The greater the steric hindrance of the substituent, the better the compatibility with organic solvents and binder resins, but the lower the melting point,
β) The longer the substituent (the higher the proportion of the molecular weight of the substituent in the total molecular weight of the compound after introduction of the substituent), the greater the steric hindrance, but the naphthalene tetracarboxylic acid diimide moiety ( The ratio of the main skeleton part) decreases, and the electron transport ability tends to be disadvantageous,
I got the knowledge.
Then, while considering such knowledge, pursuing the optimum substituent,
Focusing on alanine, the second smallest amino acid after glycine, among infinitely existing amine compounds and amino acid derivatives,
If alanine or an alanine alkyl ester is used as a substituent-introducing compound to NTC, introduction (synthesis) with high yield and purity can be easily performed, and a compound in which this substituent is introduced (hereinafter, “ In the case of “alanine derivatives”), the inventors have found that an optimum degree of steric hindrance is obtained to obtain various excellent properties (solubility, melting point, electron transport ability, etc.), and have completed the present invention.

The present invention has been made under the above-described knowledge, and the gist thereof is as follows.
(1) An electron transport material containing an alanine derivative represented by the formula (I).

In formula (I), R ₁ and R ₂ are the same or different and are alkyl groups having 6 to 16 carbon atoms.

(2) The alanine derivative is synthesized by reaction of at least one of L-alanine alkyl ester, D-alanine alkyl ester, and DL-alanine alkyl ester with naphthalene tetracarboxylic dianhydride. The electron transport material according to (1).
(3) The precursor obtained by the reaction of at least one of L-alanine, D-alanine, and DL-alanine with naphthalenetetracarboxylic dianhydride is converted into an alcohol having 6 or more carbon atoms. The electron transport material according to (1), which is synthesized by esterification.
(4) Melting | fusing point of an alanine derivative is 150 degreeC or more, The electron transport material in any one of said (1)-(3) characterized by the above-mentioned.
(5) The electron transport material according to any one of (1) to (4) above, wherein the tetrahydrofuran necessary for dissolving 1 g of the alanine derivative is 10 mL or less.

(6) An electronic material using the electron transport material according to any one of (1) to (5).
In the present specification, the alanine derivative represented by the formula (I) includes not only the DL form but also the L form and the D form.

The electron transport material of the present invention contains a novel alanine derivative and exhibits excellent electron transport ability. In addition, since it has a melting point of 150 ° C. or higher and exhibits high solubility in an organic solvent, for example, it has excellent compatibility with the binder resin that forms the photosensitive layer of an electrophotographic photosensitive member for copying machines. The temporal stability of the photosensitive layer containing the electron transport material can be obtained. Furthermore, the photosensitive layer containing the electron transport material of the present invention does not cause dripping after coating and drying on the support, and there is no risk of cracking during long-term storage.
In addition, the novel alanine derivative represented by the above formula (I) can be easily and highly purified by an original method of reacting alanine, which is the simplest structure of amino acids next to glycine, as a raw material. Since it can be synthesized in high yield, industrial scale production is also feasible.

Such an electron transport material (ETM) of the present invention is a highly sensitive and highly stable copy by combining with a known charge generating material (CGM), hole transport material (HTM), binder resin, and the like. Since a single-layer photosensitive drum for a machine can be formed, its industrial utility value is extremely high.
The ETM of the present invention can also be used for a so-called laminated photosensitive drum.

2 is a diagram showing the NMR analysis result of the compound obtained in Example 1. FIG. 2 is a diagram showing the NMR analysis result of the compound obtained in Example 2. FIG. 4 is a diagram showing a result of NMR analysis of a compound obtained in Example 3. FIG. FIG. 4 is a diagram showing the NMR analysis result of the compound obtained in Example 4. 6 is a diagram showing a result of NMR analysis of a compound obtained in Example 5. FIG. 6 is a diagram showing a result of NMR analysis of a compound obtained in Example 6. FIG. 6 is a diagram showing a result of NMR analysis of a compound obtained in Example 7. FIG. 6 is a diagram showing a result of NMR analysis of a compound obtained in Example 8. FIG. FIG. 4 is a diagram showing the NMR analysis result of the compound obtained in Comparative Example 1. FIG. 4 is a diagram showing the NMR analysis result of the compound obtained in Comparative Example 2. It is a figure which shows the NMR analysis result of the compound obtained by the comparative example 3. It is a figure which shows the NMR analysis result of the compound obtained by the comparative example 4. It is a figure which shows the NMR analysis result of the compound obtained by the comparative example 5. It is a figure which shows the NMR analysis result of the compound obtained by the comparative example 6. It is a figure which shows the NMR analysis result of the compound obtained by the comparative example 7. 2 is a diagram showing the IR analysis result of the compound obtained in Example 1. FIG. FIG. 4 is a diagram showing an IR analysis result of the compound obtained in Example 2. FIG. 4 is a diagram showing an IR analysis result of the compound obtained in Example 3. FIG. 6 is a diagram showing an IR analysis result of the compound obtained in Example 4. FIG. 6 is a diagram showing an IR analysis result of the compound obtained in Example 5. FIG. 6 is a diagram showing an IR analysis result of the compound obtained in Example 7. It is a figure which shows the IR analysis result of the compound obtained in Example 8. FIG. 4 is a diagram showing an IR analysis result of the compound obtained in Comparative Example 1. FIG. 6 is a diagram showing an IR analysis result of the compound obtained in Comparative Example 2. It is a figure which shows the IR analysis result of the compound obtained by the comparative example 3. It is a figure which shows the IR analysis result of the compound obtained by the comparative example 4. It is a figure which shows the IR analysis result of the compound obtained in the comparative example 5. It is a figure which shows the IR analysis result of the compound obtained by the comparative example 6. It is a figure which shows the IR analysis result of the compound obtained in the comparative example 7.

  The electron transport material of the present invention contains an alanine derivative represented by the above formula (I).

R ₁ and R _{2 in} formula (I) are the same or different and are an alkyl group having 6 to 16 carbon atoms, and this alkyl group may be linear or branched. Specific examples include n-hexyl, isohexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-dodecyl, 2-ethyl-1-hexyl and the like.
An alkyl group having 5 or less carbon atoms in R ₁ and R _{2 in} formula (I) does not exhibit sufficient steric hindrance, and is soluble in organic solvents (particularly tetrahydrofuran) and compatible with binder resins. Is too low. On the other hand, when the alkyl group is 17 or more, the melting point of the alanine derivative (I) to be obtained may be lowered, or the electron transport ability may be lowered.

In the present invention, in addition to the compatibility with an organic solvent and a binder resin, it is easy to chemically modify naphthalene tetracarboxylic dianhydride, naphthalene tetracarboxylic monoanhydride, naphthalene tetracarboxylic acid, etc., which are synthetic raw materials. In view of industrial costs and the like, in the above formula (I), R ₁ and R ₂ are preferably the same.
R ₁ and R ₂ are preferably a straight-chain alkyl group having 6 to 16 carbon atoms, and more preferably a straight-chain alkyl group having 6 to 9 carbon atoms.

  As for the optical isomer of the alanine derivative (I), when it is desired to obtain a compound having higher solubility, the DL form, and when obtaining a compound having a sharp melting point, the L form, D form, molecule In order to control the energy level, the D-form and the L-form can be appropriately selected depending on the application, such as mixing at an arbitrary ratio.

Thus, in the alanine derivative (I) of the present invention, a carboxylic acid ester (COOR having a “simple methyl group” and “alkyl groups R ₁ and R ₂ having 6 or more carbon atoms” on the carbon bonded to the nitrogen atom. ₁ , COOR ₂ ) ”, a very good degree of steric hindrance is exhibited, which is significantly easier and cheaper than the compound (III) described in Patent Document 2, and the column. Industrial production with high yield and purity can be reliably realized without going through a purification step by chromatography.

The alanine derivative (I) of the present invention preferably has a melting point of 120 ° C. or higher, more preferably 150 ° C. or higher.
When the melting point is less than 120 ° C., dripping may occur at the time of high-temperature drying after the photosensitive layer is coated on a drum-shaped support.

Tetrahydrofuran necessary for dissolving 1 g of the alanine derivative (I) of the present invention is preferably 10 mL or less, more preferably 5 mL or less.
If 1 g of tetrahydrofuran requires more than 10 mL of tetrahydrofuran, it may crystallize in the photosensitive layer.

(Synthesis method)
The alanine derivative represented by the above formula (I) can be synthesized by the following two reactions. That is,
It may be a method of reacting an alanine alkyl ester with naphthalenetetracarboxylic dianhydride (reaction formula (A)),
A method of reacting naphthalenetetracarboxylic dianhydride with alanine to obtain a precursor (XV), and then esterifying the precursor (XV) with an alcohol having 6 or more carbon atoms (reaction formula (B) ).
In addition, about a naphthalene tetracarboxylic dianhydride, a monoanhydride may be sufficient and it may not be an anhydride. In addition, in the following reaction formulas (A) and (B), for convenience, the case where the two alkyl groups R ₁ of the synthesized alanine derivative (I) are the same is shown, but they may be different. . If they are different, the reaction formula (A) may be reacted with two alanine alkyl esters, and the reaction formula (B) may be reacted with two alcohols.

In the reaction formulas (A) and (B), R ₁ is an alkyl group having 6 to 16 carbon atoms.

The synthesis method represented by the above reaction formula (A) is:
In this method, naphthalenetetracarboxylic dianhydride and an alanine alkyl ester having an alkyl group having 6 to 16 carbon atoms are reacted by heating and stirring while dehydrating using a Dean Stark trap or the like.
Examples of the solvent for heating and stirring include organic solvents such as dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, toluene, tetrahydrofuran, and anisole, and these may be used in combination.

The synthesis method represented by the above reaction formula (B) is:
A first step of synthesizing a precursor (XV) by reacting naphthalenetetracarboxylic dianhydride and alanine with heating and stirring while dehydrating using a Dean Stark trap or the like;
The obtained precursor (XV) comprises a second step in which esterification is carried out by heating and reacting an alcohol having 6 to 16 carbon atoms in the presence of an acid catalyst.
Examples of the solvent in the first step (when synthesizing the precursor (XV)) include organic solvents such as dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, toluene, tetrahydrofuran, and anisole. May be used.

As the solvent for the second step (esterification of the precursor (XV)), alcohols corresponding to the target esterified product (I) are used, and as a catalyst, sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, methanesulfonic acid, It is preferable to use any one of trifluoroacetic acid or a mixture thereof.
Although the usage-amount of C6-C16 alcohol with respect to a precursor (XV) weight (g) is not specifically limited, 2-100 times capacity is preferable with respect to a raw material, More preferably, it is 5-50 times capacity.

Although the synthesis method represented by the reaction formula (A) is one step, there are many cases where alanine alkyl esters having an alkyl group having 6 to 16 carbon atoms are commercially available and must be synthesized. .
On the other hand, in the synthesis method of reaction formula (B), the esterification reaction is a very safe and easy operation, and the target product (esterified product (I) to be synthesized) is used as the solvent (alcohols) used. Since it is hardly soluble, it can be obtained very easily as a crystal with high purity, and is an industrially more effective synthesis method.
The alanine derivative (I) synthesized in this way can also be purified by an adsorbent such as activated carbon, clay, silica gel.

The electronic material of the present invention uses an electron transport material (hereinafter referred to as “ETM”) containing the novel alanine derivative (I) as described above.
The ETM of the present invention is combined with, for example, a known charge generation material (hereinafter also referred to as “CGM”), a hole transport material (hereinafter also referred to as “HTM”), a binder resin, and the like. As a result, an electrophotographic photosensitive member can be formed which is used as a photosensitive layer, and the photosensitive layer is provided on a conductive support.

As the CGM that can be combined with the ETM of the present invention, a conventionally known CGM as exemplified below may be used;
[Examples of CGM that can be combined]
Phthalocyanine compounds, bisazo compounds, trisazo pigments, monoazo pigments, perylene compounds, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, indigo pigments, azurenium pigments, cyanine pigments, pyrylium salts, Ansanthrone pigments, triphenylmethane pigments, selenium pigments, toluidine pigments, pyrazoline pigments, quinacridone pigments and the like may be used alone or in combination of two or more.

Among them, metal-free phthalocyanine, aluminum phthalocyanine, vanadium phthalocyanine, cadmium phthalocyanine, antimony phthalocyanine, chromium phthalocyanine, copper 4-phthalocyanine, germanium phthalocyanine, iron phthalocyanine, dichlorotin phthalocyanine, chloroaluminum phthalocyanine, (oxy) titanyl having high photosensitivity Phthalocyanine compounds such as phthalocyanine, chloroindium phthalocyanine, chlorogallium phthalocyanine, hydroxygallium phthalocyanine, magnesium phthalocyanine, dialkyl phthalocyanine, tetramethyl phthalocyanine and tetraphenyl phthalocyanine are preferred.
As the crystal form of oxytitanyl phthalocyanine, any of α, β, γ, Y type, amorphous or mixed crystal thereof can be used. In the case of metal-free phthalocyanine, γ type can be used.
In addition, a mixture of chloroindium phthalocyanine and oxytitanyl phthalocyanine, a derivative obtained by reacting polyhydric alcohol and oxytitanyl phthalocyanine, in particular, a compound obtained by reacting butanediol and oxytitanyl phthalocyanine can be used.

As the HTM that can be combined with the ETM of the present invention, a conventionally known HTM as exemplified below may be used;
[Examples of HTMs that can be combined]
The compound represented by the following general formula (V), the compound represented by the general formula (VI), the compound represented by the general formula (VII), the compound represented by the general formula (VIII), etc. You may use, and 2 or more types may be mixed and used for it.

In the formula (V), R _{32 to} R ₃₄ are each a group consisting of a hydrogen atom, a halogen atom, an alkyl group, an allyl group, an alkoxy group, an aryl group, a dialkylamino group, and a diphenylamino group. Any one kind of substituent selected from the above, l, m, and n represent an integer of 0 or more and 2 or less.

In the formula (VI), R _{35 to} R ₃₈ are each selected from the group consisting of a hydrogen atom, an alkyl group, an allyl group, an alkoxy group, an aryl group, a dialkylamino group, and a diphenylamino group. Any one type of substituent is shown.

In formula (VII), R _{8 to} R ₁₁ represent any one type of substituent selected from the group consisting of a hydrogen atom, an alkyl group, an allyl group, and an aryl group.

In Formula (VIII), R _{12 to} R ₁₄ represent any one type of substituent selected from the group consisting of a hydrogen atom, an alkyl group, an allyl group, and an aryl group.

  Among these HTMs, preferred compounds are those that do not depend on the molecular structure but have a large molecular weight and high mobility.

In the photosensitive layer, in addition to the ETM of the present invention, conventionally known ETMs as exemplified below can be used, including compounds generally used in photoreceptors;
[Examples of other ETMs that can be combined]
These compounds such as compounds represented by the following general formulas (IX) to (XIII) may be used alone or in combination of two or more.

In formulas (IX) to (XII), R _{15 to} R ₂₅ are each a hydrogen atom, a halogen atom, an alkyl group, an allyl group, an alkoxy group, an aryl group, a dialkylamino group, and a diphenylamino group. Any one type of substituent selected from the group consisting of:

In the formula (XIII), the substituents R _{26 to} R ₃₁ are a hydrogen atom, a cyano group, a nitro group, a halogen atom, a hydroxy group, an alkyl group, an aryl group, a heterocyclic group, and an ester group. And an alkoxy group, an aralkyl group, an allyl group, an amide group, an amino group, an acyl group, an alkenyl group, an alkynyl group, a carboxyl group, a carbonyl group, and a carboxylic acid group. Any one type of substituent selected. The substituent G ₁ is any one kind of substituent selected from the group consisting of oxygen, sulfur, and ═C (CN) ₂ , and the substituent G ₂ is derived from any one element of oxygen or sulfur. Become.

As the binder resin for forming the photosensitive layer containing ETM, CGM, HTM and the like as described above, conventionally known ones exemplified below may be used;
[Example of binder resin]
Polycarbonate resin, styrene resin, acrylic resin, styrene-acrylic resin, ethylene-vinyl acetate resin, polypropylene resin, vinyl chloride resin, chlorinated polyether resin, vinyl chloride-vinyl acetate resin, polyester resin, furan resin, nitrile resin, alkyd Resin, polyacetal resin, polymethylpentene resin, polyamide resin, polyurethane resin, epoxy resin, polyarylate resin, diarylate resin, polysulfone resin, polyethersulfone resin, polyallylsulfone resin, silicone resin, ketone resin, polyvinyl butyral resin, poly Ether resin, phenol resin, EVA (ethylene / vinyl acetate) resin, ACS (acrylonitrile / chlorinated polyethylene / styrene) resin, ABS (acrylonitrile / butadiene) Styrene), such as resins and epoxy arylate These may be used alone or may be used as a mixture of two or more.

[Other additives]
In addition to the above-described components, various additives such as a plasticizer such as terphenyl, a surfactant, and a leveling agent can be added to the photosensitive layer.

For the conductive support on which the photosensitive layer as described above is formed, various materials having conductivity as exemplified below may be used;
[Example of conductive support]
Simple metals such as iron, aluminum, copper, tin, platinum, gold, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, brass; plastic materials on which the above metal is deposited or laminated, Examples thereof include glass coated with aluminum iodide, tin oxide, indium oxide, and the like; a resin substrate in which conductive fine particles such as carbon black are dispersed.
The shape of the conductive support may be any of a sheet shape and a drum shape according to the structure of the image forming apparatus to be used. The support itself has conductivity or the surface of the support is conductive. What is necessary is just to have sex. The conductive support preferably has sufficient mechanical strength when used.

Examples 1-6, Comparative Examples 1-7
Alanine derivatives having the substituents shown in Tables 1 and ₂ as R ₁ and R ₂ in Formula (I) were synthesized by the method of Reaction Formula (B) described above.

First step:
In a reaction vessel, 26,82 g (0.1 mol) of 1,4,5,8-naphthalenetetracarboxylic dianhydride, 20.49 g (0.23 mol) of DL-alanine, and 107 ml of toluene (hereinafter, And the reaction was carried out under reflux for 14 hours. During the reaction, by-product water was dehydrated using a Dean-Stark trap.
After completion of the reaction, the reaction mixture was cooled, 100 mL of hexane was added, and the precipitated crystals were filtered.
The obtained crystal was washed with water, then washed with diisopropyl ether and dried to obtain 35.8 g of a precursor (XV) (yield 87.35%).

Second step:
To 1 g of the precursor (XV) obtained in the first step, 40 mL of alkyl alcohol (alcohol for introducing substituents shown in Tables 1 and 2) and 1 drop of sulfuric acid were added, and the mixture was stirred for 8 hours. The reaction was carried out at 110 ° C. (in the case of an alkyl alcohol having a boiling point of 110 ° C. or lower, at the boiling point of the alcohol).
Next, the reaction solution was cooled to −15 ° C., and the precipitated crystals were separated by filtration to obtain a crude product.
Each obtained crude product was subjected to hot washing with methanol and then filtered to obtain alanine derivatives (I) of Examples 1 to 6 and Comparative Examples 1 to 7. Tables 1 and 2 show the weight (g) and yield (%) of each crystal obtained.
The compound of Example 6 was an oily substance without being precipitated as crystals.

Examples 7 and 8
The alanine derivative of Example 7 (S) was prepared in the same manner as in Example 3 (esterified with n-octanol) except that L-alanine or D-alanine was used instead of DL-alanine in the first step. Body), the alanine derivative (R body) of Example 8 was obtained.
Table 1 shows the weight and yield of each crystal obtained.

Comparative Examples 8 and 9
In a reaction vessel, 2,4,5,8-naphthalenetetracarboxylic dianhydride 2.97 g (0.011 mol), sodium bicarbonate 2.1 g, leucine methyl ester hydrochloride 4.64 g (0.025 mol) Alternatively, 5 g (0.025 mol) of leucine ethyl ester hydrochloride, 33 mL of toluene, and 8 mL of DMF were added and reacted for 14 hours under reflux. During the reaction, by-product water was dehydrated using a Dean-Stark trap.
After completion of the reaction, the filtrate obtained by concentrating the filtrate was subjected to column separation, and the ethyl ester was purified with methanol. Since the methyl ester could not be crystallized, it could not be purified with a solvent, and the compounds represented by the formula (III) (Comparative Examples 8 and 9) were obtained by purification only by column separation.
Table 2 shows the weight and yield of each crystal obtained.

Reference examples 1 and 2
In a reaction vessel, 1,4,5,8-naphthalenetetracarboxylic dianhydride 26.82 g (0.1 mol), (±) -2-heptylamine 24.79 g (0.215 mol) or (S) -(+)-2-Heptylamine (24.79 g, 0.215 mol) and toluene (130 mL) were added, and the mixture was reacted under reflux for 14 hours. During the reaction, by-product water was dehydrated using a Dean-Stark trap.
After completion of the reaction, the mixture was cooled, 780 mL of methanol was added, and the precipitated crystals were filtered. The resulting crude product was treated with tetrahydrofuran and activated carbon, crystallized with methanol, and Reference Example 1 represented by the formula (IV) Of the compound (racemate) and the compound of Reference Example 2 (S form) were obtained.
Table 3 shows the weight and yield of each crystal obtained.

<Melting point measurement>
The melting points of the compounds of Examples 1 to 5, 7, and 8, Comparative Examples 1 to 9, and Reference Examples 1 and 2 were measured using a melting point measuring apparatus (trade name “B545” manufactured by BUCHI, Germany). The results are shown in Tables 1-3.

<Solubility in organic solvent (THF)>
For the compounds of Examples 1 to 5, 7, and 8, Comparative Examples 1 to 9, and Reference Examples 1 and 2, the amount (mL) of tetrahydrofuran (THF) required to dissolve 1 g of each compound was measured.
The numerical value in Tables 1-3 shows the quantity which stirred for 1 minute and was dissolved completely.

<Elemental analysis>
Elemental analysis of the compounds of Examples 1 to 8 and Comparative Examples 1 to 7 was performed using a trade name “EA1108 type” manufactured by FISONS. The results are shown in Tables 1 and 2.

<NMR analysis>
NMR analysis of the compounds of Examples 1 to 8 and Comparative Examples 1 to 7 was measured with CDCl ₃ using an R-1200 type fast sweep correlation nuclear magnetic resonance apparatus (manufactured by Hitachi, Ltd.). The results are shown in FIGS.

<IR analysis>
The IR analysis of the compounds of Examples 1 to 5, 7, and 8 and Comparative Examples 1 to 7 was measured by the KBr method using an infrared spectroscopic analyzer (trade name “Nicole 380” manufactured by Thermo Corporation). The results are shown in FIGS.

<Photoconductor characteristics as ETM>
For the compounds of Examples 1 to 8, Comparative Examples 8 and 9, and Reference Examples 1 and 2, the photoreceptor characteristics were evaluated as follows (note that it is necessary to dissolve 1 g in the solubility test described above). In Comparative Examples 1 to 7 in which the amount of THF exceeded 10 mL, crystallization and the like were observed during the preparation of the coating solution, a sufficient photosensitive layer could not be formed, and evaluation of the photoreceptor characteristics was impossible. );
As CGM, 0.1 g of α-type oxytitanyl phthalocyanine was added to 100 mL of tetrahydrofuran together with 4.7 g of Z-type polycarbonate having a molecular weight of 40,000, and dispersed in an ultrasonic disperser for 24 hours.
Thereto, 1.7 g of each of the compounds of Examples 1 to 8, Comparative Examples 8 and 9, and Reference Examples 1 and 2 as ETM, and m-TPD (N, N′— represented by the above formula (V) as HTM Diphenyl-N, N′-di (m-tolyl) benzidine) (3.5 g) was added and mixed and dissolved to obtain a coating solution.

Each of the obtained coating liquids was applied to a drum-shaped conductive support made of aluminum with a single coating application device manufactured by Mitsubishi Materials Techno Corporation so that the film thickness was 30 μm. An electrophotographic photoreceptor having a layer-type photosensitive layer was produced.
In order to evaluate the sensitivity of the produced electrophotographic photosensitive member, a half exposure amount (μJ / cm ² ) was measured using an electrophotographic evaluation apparatus “CINDIE 743” manufactured by Gentec Corporation. The results are shown in Table 4.
The half-exposure amount is an exposure amount necessary to halve the surface potential when the surface of the charged photosensitive layer (photoconductive layer) is exposed. The smaller the half-exposure amount, the more sensitive the photoreceptor is. This is a value indicating the sensitivity of the electrophotographic photosensitive member indicating that it is large.

For the evaluation of half-exposure dose, in general, in a positively charged single-layer photoreceptor using α-type oxytitanyl phthalocyanine, when it is 0.25 μJ / cm ² or less, the sensitivity is good (high sensitivity), and 0.30 μJ / cm ^If it exceeds about ² , it is insufficient as a photosensitive drum and is considered to be defective.

The alanine derivative of the present invention is a novel compound that is very excellent in solubility in organic solvents as well as electron transport ability.
Therefore, for example, it is extremely useful as an electron transport material (ETM) for an electrophotographic photosensitive member used in an image forming apparatus such as an electrostatic copying machine, a facsimile machine, a laser beam printer, etc., but also an organic semiconductor, an organic EL, It can be suitably used in a wide range of fields such as conductive polymers.

Claims (6)

An electron transport material containing an alanine derivative represented by the formula (I).
Wherein _{(I), R 1, R} 2 are the same or different, is an alkyl group having 6 to 16 carbon atoms.   The alanine derivative is synthesized by a reaction of at least one of L-alanine alkyl ester, D-alanine alkyl ester, and DL-alanine alkyl ester with naphthalenetetracarboxylic dianhydride. 2. The electron transport material according to 1.   The alanine derivative is obtained by esterifying a precursor obtained by reaction of at least one of L-alanine, D-alanine, and DL-alanine with naphthalenetetracarboxylic dianhydride with an alcohol having 6 or more carbon atoms. The electron transport material according to claim 1, wherein the electron transport material is synthesized.   The melting point of said alanine derivative is 150 degreeC or more, The electron transport material as described in any one of Claims 1-3 characterized by the above-mentioned.   The electron transport material according to any one of claims 1 to 4, wherein tetrahydrofuran required for dissolving 1 g of the alanine derivative is 10 mL or less.   The electronic material using the electron transport material as described in any one of Claims 1-5.