JP2006171321A - Organic photorefractive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic photorefractive material which can form a diffraction grating, without external electric field and which has a small light absorption coefficient. <P>SOLUTION: The organic photorefractive material includes the components (A) an organic photoconductive compound; (B) a sensitizer; (C) a plasticizer; and (D) at least one kind of compounds selected from among cyanobiphenyls, azomethines, and cyanophenylbenzoates, as an field responsive optical functional compound. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to organic photorefractive materials. The photorefractive material of the present invention provides excellent photorefractive characteristics without voltage application, and can be used in application fields such as optical communication and optical recording.

(Photorefractive material)
A photorefractive material is a material in which a spatial electric field is generated when irradiated with light, and the refractive index changes correspondingly. When the photorefractive material is irradiated with interference light, carriers are generated only in the bright part of the interference light, so that a spatial electric field corresponding to the light intensity distribution of the interference light is generated, and a corresponding refractive index modulation is generated to form a diffraction grating. . The diffraction grating formed in this way is out of phase (π / 2) with the intensity distribution (interference fringes) of the interference light, and therefore between one light beam incident on the material and the other light beam. Energy transfer occurs.

  Therefore, application to an optical modulation element that performs nonlinear signal processing on signal light is possible by utilizing such characteristics. That is, the hologram recording material using the formation of the diffraction grating, the optical switching element using the energy transfer, and the diffracted light generated from the diffraction grating are phase conjugate, and therefore can be used as a phase conjugate mirror.

  As such a photorefractive material, a photorefractive material (hereinafter referred to as an organic photorefractive material) that uses an amorphous organic compound and has excellent molding processability instead of an inorganic photorefractive material that has been known for a long time. ) Is required. For such organic photorefractive materials, an organic photoconductive compound for forming a spatial electric field and an electric field response optical functional compound (such as a nonlinear optical dye) that causes a change in refractive index corresponding to the spatial electric field are essential. Further, as necessary, a sensitizer for improving the absorption efficiency of irradiation light and a plasticizer for improving molding processability are also added.

In the past research, mainly high-molecular compounds having photoconductive function were compounded with electric field response optical functional compounds such as nonlinear optical dye compounds, and conversely, low-molecular compounds having photoconductive function in polymers containing nonlinear optical dyes. Various proposals have been made, such as those blended as a polymer, or a polymer inert to photorefractive properties such as polymethylmethacrylate and polystyrene as a binder material, and a compound containing a photoconductive function and a non-linear optical dye as a low molecule.
JP2003-322886 Japanese Patent Laid-Open No. 2004-210693

However, the conventional photorefractive material has a low light transmittance and, for example, when used for a volume hologram recording material, a sufficient thickness of the material cannot be ensured. An object of the present invention is to provide an organic photorefractive material which can form a diffraction grating without an external electric field and has a sufficiently small light absorption coefficient.
As a result of intensive studies on such problems, the present inventors have found that the light transmittance of a material can be improved by blending a specific compound as an electric field response optical functional compound to be blended with a photorefractive material. As a result, the present invention has been completed.

The present invention provides an organic photorefractive material comprising the following components A, B, C and D:
A: Organic photoconductive compound B: Sensitizer C: Plasticizer D: At least one compound selected from cyanobiphenyls, azomethines and cyanophenylbenzoates as an electric field responsive optical functional compound is provided. is there. In a preferred embodiment of the organic photorefractive material of the present invention, the organic photoconductive compound is poly (N-vinylcarbazole), the sensitizer is 2,4,7-trinitro-9-fluorenone, and the plasticizer is 2- (1,2-cyclohexanedicarboximido) ethyl propionate. In the organic photorefractive material, the blending amount of component A is 10 to 50% by weight, the blending amount of component B is 0.01 to 20% by weight, and the blending amount of component C is 5 to 50% by weight. And it is preferable that the compounding quantity of the component D is 1 to 60 weight%.

  According to the present invention, an organic photorefractive material having a small light absorption coefficient is obtained by using at least one compound selected from rod-shaped molecules, that is, cyanobiphenyls, azomethines and cyanophenylbenzoates as an electric field response optical functional compound. Obtainable.

Detailed description of the invention

A: Organic photoconductive material Examples include vinyl polymers and addition condensation polymers. For example, poly (N-vinylcarbazole), polyvinylxylene, polyvinylnaphthalenes, polyvinylpyrenes, polyvinylquinoline, polyacenaphthylene, and other aromatic rings. A vinyl compound is mentioned. In addition, homopolymers and copolymers of vinyl compounds using triphenylamine derivatives may be mentioned.

  In particular, poly (N-vinylcarbazole) is preferable in terms of high compatibility with other functional materials. The blending amount of Component A is preferably 10 to 50% by weight based on the total composition. If the amount of the organic photoconductive compound is less than this, the photocharge generation efficiency may be reduced, and problems such as a decrease in charge transport ability may occur. On the other hand, when the amount is larger than the above range, the concentration of other components necessary for the expression of the photorefractive characteristic is lowered, and the photorefractive characteristic is lowered.

B: Sensitizer The organic photorefractive material of the present invention needs a sensitizer to absorb light. It is known that a sensitizer forms a charge transfer complex with a photoconductive compound, absorbs light to generate a carrier, and the generated carrier is transported by an organic photoconductive material.
As the sensitizer, a sensitizer having an electron-withdrawing group is preferable, and examples thereof include fluorenones having an electron-withdrawing nitro group. Specific examples include fluorene derivatives such as 2,4,7-trinitro-9-fluorenone (TNF), 2,4,7-trinitro-9-fluorenylidene malonitrile, and 2,4-dinitrofluorene. In addition, thioxanthenes such as 9-oxo-9H-thioxanthene-3-carboxylic acid-10,10-dioxide, 9-oxo-9H-thioxanthene-3-carboxamide-10,10 dioxide, tetracyanoethylene, Cyanoethylenes such as 7,7,8,8-tetracyanoquinodimethane and fullerenes such as C ₆₀ and C ₇₀ are also preferred. Of these, 2,4,7-trinitro-9-fluorenone is particularly preferable because it has good compatibility with other functional compounds and has strong electron withdrawing properties.

  The blending amount of such a sensitizer is preferably 0.01 to 20% by weight, more preferably 0.1 to 20% by weight in the organic photorefractive material. When the amount of the sensitizer is less than this range, the carrier generation efficiency is low. On the other hand, if the amount exceeds this range, the amount of charge generation increases, but the light absorption of the charge transfer complex generated from the sensitizer and the organic photoconductive compound becomes too strong, and the photorefractive material is used as a light modulation element. This causes a decrease in signal light intensity.

C: Plasticizer In the present invention, the plasticizer serves as a solvent or compatibilizer for uniformly mixing the above-described components, and improves the moldability of the material. Examples of such plasticizers include 2- (1,2-cyclohexanedicarboximido) ethyl propionate, 2- (1,2-cyclohexanedicarboximido) ethyl butyrate, 2- (1,2-cyclohexanedioxylate). Carboximido) ethyl benzoate, 2- (1,2-cyclohexanedicarboximido) ethyl acrylate, 2- (phthalimido) ethyl propionate, tricresyl phosphate, dioctyl phthalate, butyl benzyl phthalate, dibutyltin Common plasticizers such as dilauric acid esters can be mentioned. Of these, 2- (1,2-cyclohexanedicarboximido) ethyl propionate (AX22) is preferred because of its good compatibility with other functional components.

  The blending amount of the plasticizer is preferably 5 to 50% by weight in the photorefractive material. When the amount of the plasticizer is less than this range, phase separation such as crystal precipitation occurs. On the other hand, when it exceeds this range, the compounding quantity of another functional compound will fall and the characteristic of a photorefractive material will fall inevitably.

D: Field-responsive optical functional compound In the conventional photorefractive material, a charge transfer complex is formed by a sensitizer and a photoconductive material, and a spatial electric field necessary to cause a photorefractive effect without applying an external electric field is formed. Then, an electric field response optical functional compound such as a nonlinear optical dye responds to this to induce refractive index modulation, thereby forming a diffraction grating. In the photorefractive material of the present invention, at least one compound selected from cyanobiphenyls, azomethines, and cyanophenylbenzoates is used as the electric field response optical functional compound. Specifically, as cyanobiphenyls (formula D1), 4-cyano-4′-n-heptyloxybiphenyl and the like; phenylbenzoates (formula D2, formula D3) as cyanophenylbenzoate, 4-nitrophenyl salicylate, etc. Azomethines (formula D4) include 4-[(4-methoxybenzylidene) amino] benzonitrile and the like.
Since these compounds are rod-like molecules, they have a small light absorption coefficient, a large birefringence, and a large change in refractive index during orientation, so that a diffraction grating can be formed without an external electric field.

(式中、Ｒは炭素数１〜１３のアルキル基)

(式中、Ｘはニトロ基又シアノ基であり、ｎは０〜３の整数である。)

(式中、Ｒは水素原子又は炭素数１〜６のアルキル基であり、Ｘはニトロ基又はシアノ基である。)

(式中、Ｒは水素原子又は炭素数１〜６のアルキル基であり、Ｘはニトロ基又シアノ基である。)

(Wherein R is an alkyl group having 1 to 13 carbon atoms)

(In the formula, X is a nitro group or a cyano group, and n is an integer of 0 to 3.)

(In the formula, R is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and X is a nitro group or a cyano group.)

(In the formula, R is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and X is a nitro group or a cyano group.)

The blending amount of the electric field response optical functional compound is preferably 1 to 60% by weight, more preferably 10 to 30% by weight, based on the entire photorefractive material. If the blending amount is less than the above range, refractive index modulation does not occur and a diffraction grating is not formed. On the other hand, if the blending amount is larger than the above range, crystallization or phase separation occurs and recording becomes impossible due to light scattering.
Furthermore, other electric field response optical functional compounds may be added if necessary. Such electric field responsive optical functional compounds include compounds having an electron-donating group such as an amino group, a hydroxy group or an ether group and an electron-withdrawing group such as a cyano group or a nitro group in the molecule, or a rigid group such as a benzene skeleton. Examples thereof include compounds having a large polar functional group bonded through a skeleton.

(Preparation of photorefractive molding)
A method for producing a photorefractive molded article using each of the above components will be described. The solid content in the photorefractive molded body needs to be mixed uniformly. Therefore, the solid content is dissolved in a highly polar solvent and sufficiently stirred and mixed until uniform. The solid content concentration in the solvent may be a concentration that allows uniform dissolution, but the solid content concentration should be 1 to 20% by weight so that operations such as solution viscosity at the time of mixing and drying necessary for film formation are easy. It is preferred to dissolve.

Using the mixed solution thus obtained, a film is produced by a casting method or the like to produce a practical photorefractive material. In addition, the form of the photorefractive material of this invention is not limited to a film, It can shape | mold into a suitable form according to the intended purpose.
For example, in order to create a film by a casting method, a smooth film surface is obtained by directly applying a film on a substrate such as a glass plate by spin coating or dripping, and casting a solution according to a desired film thickness and shape. Get. Next, the solvent is removed from the cast solution by heating or the like under reduced pressure to form a film.

Next, the present invention will be described more specifically with reference to examples and comparative examples.
[Examples 1 to 4, Comparative Example 1]
(Sample preparation)
A: Organic photoconductive child compound Poly (N-vinylcarbazole) manufactured by Aldrich was purchased and used after reprecipitation and purification.

B: Sensitizer 2,4,7-trinitro-9-fluorenone manufactured by Tokyo Chemical Industry Co., Ltd. was purchased and used as it was.

フタル酸無水物１４９ｇ(967mmol)にトルエン２００mlとエタノールアミン６２ｇ(1000mmol)を加えて８０℃で２時間攪拌した後、チタンブタネートを１５ｇ(44mmol)を加えて還流を１９時間行った。冷却後反応溶液に水100mlを加えることで析出する白色沈殿物を濾別して有機層を回収した。溶媒を留去して得られる反応混合物をカラムクロマトグラフィー(充填剤：シリカゲル、展開溶媒：ｎ−ヘキサンと酢酸エチルの混合溶媒)で精製してＮ−(２−ヒドロキシエチル)シクロヘキサンジカルボキシイミドを得た(２００g）。
Ｎ−(２−ヒドロキシエチル)シクロヘキサンジカルボキシイミド５２ｇ(２７２mmol)にピリジン５７ml、トルエン２００ml、プロピオン酸クロライド３０ml(３４７mmol)を加えて９０℃で１９時間攪拌した。反応混合物を希塩酸水、炭酸水素ナトリウム水溶液、食塩水の順で洗浄し有機層を回収した。溶媒を留去して得られる反応混合物をカラムクロマトグラフィー(充填剤：シリカゲル、展開溶媒：ｎ−ヘキサンと酢酸エチルの混合溶媒)で精製し目的物を得た。収量４５ｇ、収率６５％ C: Plasticizer 2- (1,2-cyclohexanedicarboximido) ethyl pyropionate (AX22) was synthesized according to the following method.

To 149 g (967 mmol) of phthalic anhydride, 200 ml of toluene and 62 g (1000 mmol) of ethanolamine were added and stirred at 80 ° C. for 2 hours, and then 15 g (44 mmol) of titanium butanate was added and refluxed for 19 hours. After cooling, 100 ml of water was added to the reaction solution, and the white precipitate that precipitated was collected by filtration to recover the organic layer. The reaction mixture obtained by distilling off the solvent was purified by column chromatography (filler: silica gel, developing solvent: mixed solvent of n-hexane and ethyl acetate) to obtain N- (2-hydroxyethyl) cyclohexanedicarboximide. Obtained (200 g).
To 52 g (272 mmol) of N- (2-hydroxyethyl) cyclohexanedicarboximide, 57 ml of pyridine, 200 ml of toluene and 30 ml (347 mmol) of propionic acid chloride were added and stirred at 90 ° C. for 19 hours. The reaction mixture was washed with diluted hydrochloric acid, sodium bicarbonate aqueous solution, and brine in this order to recover the organic layer. The reaction mixture obtained by distilling off the solvent was purified by column chromatography (filler: silica gel, developing solvent: mixed solvent of n-hexane and ethyl acetate) to obtain the desired product. Yield 45g, Yield 65%

４−シアノ−４'−ｎ−ヘプチルオキシビフェニル

シアノフェニルベンゾエート

４−ニトロフェニルサリチレート；

４−[(４−メトキシベンジリデン)アミノ]ベンゾニトリル

７ＤＣＳＴ D: Electric field response optical functional compound

4-cyano-4'-n-heptyloxybiphenyl

Cyanophenyl benzoate

4-nitrophenyl salicylate;

4-[(4-Methoxybenzylidene) amino] benzonitrile

7DCST

(Preparation of photorefractive material and evaluation method thereof)
The above components A to D were added to tetrahydrofuran in the formulation shown in Table 1 and dissolved. This solution was filtered through a polytetrafluoroethylene membrane to remove impurities such as dust, and then heated and dried at 70 ° C. overnight, and tetrahydrofuran was completely distilled off to obtain a uniformly mixed solid. This solid content was sandwiched between glass beads as spacers on a glass plate to obtain a film having a thickness of 100 μm, and a sample for characteristic evaluation was obtained.
When the obtained sample was subjected to interference exposure using a helium neon laser as a light source, it was confirmed that a diffraction grating was formed without an external electric field. The absorption coefficient was measured by measuring the absorbance at 633 nm using a JASCO UV-visible spectrophotometer (V-560). The measurement results are summarized in Table 1.

(result)
The organic photorefractive material of the example containing the field response optical functional compound has a smaller light absorption coefficient than that of the comparative example.

Claims (3)

An organic photorefractive material comprising the following components A, B, C and D.
A: Organic photoconductive compound B: Sensitizer C: Plasticizer D: At least one compound selected from cyanobiphenyls, azomethines and cyanophenylbenzoates as electric field responsive optical functional compounds The organic photoconductive compound is poly (N-vinylcarbazole), the sensitizer is 2,4,7-trinitro-9-fluorenone, and the plasticizer is 2- (1,2-cyclohexanedicarboximido) ethyl pro The organic photorefractive material of claim 1 which is a pioneate. In the organic photorefractive material, the blending amount of component A is 10 to 50% by weight, the blending amount of component B is 0.01 to 20% by weight, the blending amount of component C is 5 to 50% by weight, and The organic photorefractive material according to claim 1, wherein the blending amount is 1 to 60% by weight.