JP2007041324A - Organic photorefractive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic photorefractive material in which a diffraction grating can be formed without an external electric field and the writing efficiency during re-recording is little lowered.
[Solution]
An organic photorefractive material comprising the following components A, B, C, D and E.
A: Organic photoconductive compound B: Sensitizer C: Plasticizer D: Electric field response optical functional compound E: Antioxidant [Selection] None

Description

  The present invention relates to organic photorefractive materials. The photorefractive material of the present invention can provide excellent photorefractive characteristics without voltage application, and can be used in fields such as optical communication and optical recording with little light deterioration even when repeated recording is performed.

(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. . Since such a diffraction grating is out of phase (π / 2) with the intensity distribution (interference fringes) of interference light, energy transfer occurs between one light beam incident on the material and the other light beam.

  Therefore, by utilizing such characteristics, it can be used for an optical modulation element that performs nonlinear signal processing on signal light. 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, an amorphous organic compound is used instead of an inorganic photorefractive material known for a long time, and a photorefractive material excellent in molding processability at low cost (hereinafter referred to as an organic photorefractive material). Is required. For 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 refractive index change corresponding to the spatial electric field are essential. In addition, a sensitizer and a plasticizer are added to improve the processability of the sensitizer and the molding processability as needed.

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. There are various proposals such as those blended as a polymer, or a polymer inactive with respect to photorefractive properties such as polymethyl methacrylate and polystyrene as a binder material, and a blend of a photoconductive function and a non-linear optical dye with a low molecular weight.
JP2003-322886 Japanese Patent Laid-Open No. 2004-210693

  These photorefractive materials can be used as rewritable optical recording materials in which once recorded diffraction gratings can be erased by a heating operation or the like. However, when the diffraction grating is recorded, the material is lightly deteriorated, and when the diffraction grating is recorded repeatedly, the writing efficiency is greatly reduced. An object of the present invention is to provide an organic photorefractive material that suppresses such photodegradation and causes little decrease in writing efficiency. As a result of intensive studies on such problems, the present inventors have obtained the knowledge that photodegradation of a material can be prevented by incorporating an antioxidant into the photorefractive material, and the present invention has been completed. It was.

The present invention provides an organic photorefractive material comprising the following components A, B, C, D and E:
A: Organic photoconductive compound B: Sensitizer C: Plasticizer D: Electric field response optical functional compound E: An antioxidant is provided. In a preferred embodiment of the organic photorefractive material of the present invention, the antioxidant is a phenol-based or aromatic amine-based antioxidant. This organic photorefractive material has an organic photoconductive compound of poly-N-vinylcarbazole, a sensitizer of 2,4,7-trinitro-9-fluorenone, and a plasticizer of 2- (1,2-cyclohexanedicarboximide) ) Ethyl propionate, the field response optical functional compound is N- (4-nitrophenyl) -L-prolinol, and the antioxidant is 2,6-di-tert-butyl-4-methylphenol, hydroquinone, Particularly preferred is at least one antioxidant selected from N, N′-diphenyl-p-phenylenediamine.

  According to the present invention, the photodegradation of an electric field response optical functional compound such as a nonlinear optical dye can be suppressed by blending an antioxidant, and a decrease in writing efficiency at the time of re-recording can be prevented.

Detailed description of the invention

A: Organic photoconductive materials Vinyl polymers, addition condensation polymers, and the like, for example, poly-N-vinylcarbazole (PVK), polyvinyl xylene, polyvinyl naphthalenes, polyvinyl pyrenes, aromatic rings such as polyvinyl quinoline and polyacenaphthylene Vinyl compounds having In addition, homopolymers and copolymers of vinyl compounds using triphenylamine derivatives may be mentioned.

  In particular, poly-N-vinylcarbazole is preferable because of its 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 blending amount of the organic photoconductive compound is less than this, 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: Electric field responsive optical functional compound The electric field responsive optical functional compound used in the present invention is preferably a compound containing a nitrogen or oxygen atom having an unshared electron pair and conjugated with an aromatic ring such as a benzene skeleton. A compound in which a functional group having a large polarity is bonded via a rigid skeleton such as a benzene skeleton is preferable because the birefringence of the molecule is increased.
Examples of such compounds include azo compounds such as disperse red and 2,5-dimethyl-4- (p-nitrophenylazo) anisole, 2-cyano-3- (4-dimethylamino-phenyl) -buta-2. -Cyanoethylenes such as ene-dinitrile, 2-methyl-nitroaniline, N-methyl-4-nitro-o-toluidine, [[4- (hexahydro-1H-azepin-1-yl) phenyl] methylene] propanedi Nitroanilines such as nitrile (7DCST), N- (4-nitrophenyl) -L-prolinol (NPP) and the like can be mentioned. In particular, N- (4-nitrophenyl) -L-prolinol is preferable because of its high diffraction grating formation efficiency under no electric field conditions, and good compatibility with other functional materials and good thermal stability. The compounding amount of the electric field response optical functional compound is preferably 0.01 to 50% by weight in the photorefractive material. If the blending amount is less than this, a diffraction grating is not formed. On the other hand, if the blending amount is too large, crystallization or phase separation occurs and recording is impossible due to light scattering.

E: Antioxidant Phenol derivatives and aromatic amine-based commercially available antioxidants can be used as the antioxidant used in the photorefractive material of the present invention.
As phenolic antioxidants, 2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol (BHT), 2,4, 6-tri-tert-butylphenol, hydroquinone, 2,5-di-tert-butylhydroquinone, 4,4'-methylene-bis- (2,6-di-tert-butylphenol), 2,2'-ethylidenebis- (2,4-di-tert-butylphenol), 2,2'-methylenebis- (4-ethyl-6-tert-butylphenol), 2,2'-methylenebis- (6-cyclohexyl-4-methylphenol), 2 2,2'-thiobis- (4-methyl-6-tert-butylphenol), 4,4'-thiobis- (3-methyl-6-tert-butylphenol), 2,2'-methylenebis- (4-m-ethyl) -6-tert-butylphenol), Lis (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) ) Benzene and the like.

Aromatic amine antioxidants include diphenylamine, alkyl derivatives thereof, N, N′-diphenyl-p-phenylenediamine, allyl derivatives thereof, N-phenyl-N′-isopropyl-p-phenylenediamine, N-phenyl- β-naphthylamine, aldol-α-naphthylamine, N, N′-di-2-naphthyl-N′-isopropyl-p-phenylenediamine and the like can be mentioned.
The blending amount of these antioxidants is preferably 0.01 to 5% by weight with respect to the photorefractive material. If the blending amount of the antioxidant is out of this range, the compatibility with other functional materials is lowered and the diffraction grating formation efficiency is lowered.

(Preparation of photorefractive molding)
In order to produce the photorefractive molded article of the present invention, the above components are dissolved in a highly polar solvent and stirred and mixed until uniform. The solid content concentration of the solvent may be a concentration at which uniform dissolution is possible, but the solid content concentration is preferably 1 to 20% by weight so that the solution viscosity at the time of mixing and the drying operation at the time of film formation are easy.

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 3, Comparative Example 1]
(Sample preparation)
Organic photoconductive compound: Poly (N-vinylcarbazole) purchased from Aldrich was used after reprecipitation and purification.
Sensitizer: 2,4,7-trinitro-9-fluorenone was purchased from Tokyo Chemical Industry Co., Ltd. and used as it was.

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%

Electric field response optical functional compound: N- (4-nitrophenyl) -L-prolinol (NPP) manufactured by Tokyo Chemical Industry Co., Ltd. was used as it was.
Antioxidants: 2,6-di-tert-butyl-4-methylphenol (BHT), hydroquinone, and N, N′-diphenyl-p-phenylenediamine were all commercially available products.

(Preparation of photorefractive material and evaluation method thereof)
Components A to E were added to tetrahydrofuran and dissolved at respective blending ratios shown in Table 1 below. 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, formation of a diffraction grating was confirmed without an external electric field.

また回折格子を記録した後、試料ホルダをヒータで５０〜８０℃に加熱して回折格子を消去し、室温に戻した後再び干渉露光を行い回折効率を求めた。結果を表１に示す。 For the measurement of diffraction efficiency, a 14 mW helium neon laser was used as a light source. This light source was divided into two s-polarized lights having an equivalent intensity (about 500 mW / cm ² ) using a beam splitter or the like. The two s-polarized lights were irradiated to the evaluation sample as writing light, and interference light irradiation was performed until no more diffraction gratings were formed. One of the two writing lights was blocked every predetermined time, the transmitted light and the diffracted light were measured, and the diffraction efficiency was determined according to the following equation.

Further, after recording the diffraction grating, the sample holder was heated to 50 to 80 ° C. with a heater to erase the diffraction grating, and after returning to room temperature, interference exposure was performed again to obtain diffraction efficiency. The results are shown in Table 1.

Claims (3)

An organic photorefractive material comprising the following components A, B, C, D and E.
A: Organic photoconductive compound B: Sensitizer C: Plasticizer D: Electric field response optical functional compound E: Antioxidant 2. The organic photorefractive material according to claim 1, wherein the antioxidant is a phenol-based or aromatic amine-based antioxidant. The organic photoconductive compound is poly-N-vinylcarbazole,
The sensitizer is 2,4,7-trinitro-9-fluorenone,
The plasticizer is 2- (1,2-cyclohexanedicarboximido) ethyl propionate;
The field response optical functional compound is N- (4-nitrophenyl) -L-prolinol and the antioxidant is 2,6-di-tert-butyl-4-methylphenol, hydroquinone, N, N′-diphenyl The organic photorefractive material according to claim 1, which is at least one antioxidant selected from -p-phenylenediamine.