JPH0736008A - Optical modulation element - Google Patents

Abstract

PURPOSE:To provide a material for photo-photo modulation element having a high density, high sensitivity and excellent stability and simple constitution and to make it possible to non-destructively read out a written memory by using this optical modulation element material. CONSTITUTION:The optical modulation element material consists of a high- polymer liquid crystal film 3 formed by subjecting a side chain type high- polymer liquid crystal contg. a photochromic compd. as one component to a twist orientation treatment. This photochromic compd. modulates the light of a wavelength region without having absorption by a change of the high- polymer liquid crystal film 3 generated according to the photoisomerization of the photochromic compd. The high-polymer liquid crystal film 3 consists of the side chain type high-polymer liquid crystal having the photochromic component covalent-bonded to the side chain or is composed of the side chain type high-polymer liquid crystal in which the photochromic compd. is dispersed. Further, a low-molecular liquid crystal may be contained therein.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel light modulator, and more particularly to a light modulator using a photochromic compound which can be applied to a stable and high-density optical arithmetic device or an optical memory.

[0002]

2. Description of the Related Art Conventionally, as a light modulation element, one utilizing an electro-optical effect, a magneto-optical effect, an acousto-optical effect, etc. is known. The electro-optic effect utilizes the change in refractive index due to the application of an electric field, and the magneto-optic effect utilizes that the plane of polarization rotates due to the magnetic field. Also, in the acousto-optic effect,
For example, a high frequency voltage is applied to a transducer composed of a comb-shaped electrode formed on a waveguide to generate a surface acoustic wave corresponding to the frequency of an input signal, and the interaction between the guided light and the surface acoustic wave causes the guided light to travel. The fact that the polarization angle changes is used. As described above, in the conventional light modulation element, since the light modulation is performed by applying the electric field or the magnetic field, there is a limit to high definition and high speed. Therefore, research has been conducted on elements that can perform optical modulation using light. As an element that performs optical modulation using conventional light,
(1) A light modulation device that combines a photoconductive device and a liquid crystal device, (2) A light modulation device that uses a mixture of a ferroelectric liquid crystal and a photochromic compound (Proceedings of the 17th Liquid Crystal Symposium: page 246) ( 3) An optical modulator (Japanese Patent Laid-Open No. 2-190827) has been proposed in which the transition moment of the photochromic compound is oriented in a certain direction and the change in birefringence of the photochromic compound due to photoisomerization is utilized.

[0003]

In the cases (1) and (2) described above, the electro-optical effect is essentially used, and power consumption becomes a problem. In case (1), the process is complicated because the photoconductive element and the liquid crystal element are laminated, and in case (2), the structure is simple, but the bistable state of the ferroelectric liquid crystal is used. Therefore, there are problems such that only binary modulation can be performed, or the operating temperature range is narrow. Further, in the case of (3), there is a problem that sufficient contrast cannot be obtained because the birefringence change due to photoisomerization is small. An object of the present invention is to solve the above problems in the prior art,
It is an object of the present invention to provide an optical-optical modulator having a high density, high sensitivity, and excellent stability and a simple structure.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that in a side chain type polymer liquid crystal subjected to a twist (twist) orientation treatment, a polymer liquid crystal medium induced by a photochromic reaction The inventors have found that the change modulates light in the wavelength region that does not have absorption of the photochromic compound, and completed the present invention.

The light modulator of the present invention comprises a polymer liquid crystal film obtained by subjecting a side chain type polymer liquid crystal containing a photochromic compound as one component to a twist alignment treatment, and photochromic light in a wavelength range where the photochromic compound does not absorb light. It is for modulation by the change of the polymer liquid crystal film caused by the photoisomerization of the compound.

In the present invention, the polymer liquid crystal film comprises
A low molecular weight liquid crystal can be mixed for the purpose of increasing the change in refractive index anisotropy induced by the photochromic reaction, increasing the response speed, or expanding the operating temperature range. The low-molecular liquid crystal described here may be a commonly known nematic liquid crystal having a single composition or a liquid crystal composition. Therefore, one of the preferred optical modulators of the present invention is one in which the polymer liquid crystal film is composed of at least two components, a side chain polymer liquid crystal having a photochromic component covalently bonded to a side chain and a low molecular liquid crystal. The other is that the polymer liquid crystal film is composed of at least three components of a side chain polymer liquid crystal, a photochromic compound and a low molecular liquid crystal.

The present invention will be described in detail below. The light modulating material used in the light modulating element of the present invention is composed of at least a side chain type polymer liquid crystal and a photochromic compound as essential components. The constitution is (1) in the first embodiment, A polymer liquid crystal in which a photochromic compound is dispersed is used, and in the second aspect (2), a side chain to which the photochromic compound is bonded by a covalent bond is used.

First, the case of the optical modulator of the first aspect (1) will be described. Here, the side chain type polymer liquid crystal is a polymer having a mesogenic molecule showing liquid crystallinity in a pendant side chain through a predetermined alkyl spacer, and like the low molecular weight liquid crystal, a nematic phase, a smectic phase or a cholesteric phase. It forms various liquid crystal phases such as phases. Regarding the side chain type polymer liquid crystal used, its structure is described in Mol. Cryst. Liq. Cryst. , 16
7, 169 (1989) and the like. For example, cyanobiphenyl, cyanophenylbenzoate, cyanobiphenylbenzoate, cyanophenyl (4-phenylbenzoate) having a positive dielectric anisotropy, or
Methoxybiphenyl, methoxyphenylbenzoate, methoxybiphenylbenzoate having a negative dielectric anisotropy,
It is possible to use a general one having a methoxyphenyl (4-phenylbenzoate) structure and having a main chain structure of polyacrylate type, polymethacrylic type, polyether type, polyester type, polysiloxane type or the like. Specific examples thereof include those composed of monomer units represented by the following general formulas (V) to (VIII), but are not limited thereto.

[0009]

[Chemical 3] [R ¹¹ represents a hydrogen atom or a methyl group, and X and Y are a single bond, —O—, —COO—, and —OCO, respectively.
Represents-, -CH = N- or -N = CH-, and R
¹² represents an alkyl group, an alkoxy group, a carboxyl group, a fluoroalkyl group, a fluoroalkoxy group, a cyano group, a halogen atom or a hydrogen atom, and Φ ¹ and Φ ² are
Representing the following groups respectively,

[0010]

[Chemical 4] (Wherein Q represents a hydrogen atom, a fluorine atom, a chlorine atom or a bromine atom, m represents 0 or an integer of 1 to 4), n represents an integer of 2 to 30, and p represents 1 to 20. Represents the integer. The molecular weight (weight average molecular weight) of the polymer liquid crystal is preferably in the range of 1,000 to 1,000,000, more preferably in the range of 1,000 to 50,000. Further, those having a Tg (glass transition point) of 50 ° C. or lower exhibit high modulation characteristics and are therefore preferable.

As the photochromic compound dispersed in the above side chain type polymer liquid crystal, G. H. Brown
Various compounds described in the book "Photochromism" can be mentioned. For example, spiropyran derivatives,
Examples include spirooxazine derivatives, azobenzene derivatives, fulgide derivatives, diarylethene derivatives, triarylmethane derivatives and indigo derivatives. In particular, a fulgide derivative or a diarylethene derivative, which is a photon-mode photochromic compound that does not cause thermal isomerization, is preferably used from the viewpoint of improving recording stability. Further, in particular, the thermostable photochromic compound represented by the following formula (I) or (II) is preferable because it has improved compatibility with a polymer liquid crystal and has a large effect as a dopant.

[0012]

[Chemical 5] [Wherein R ^{1 to} R ⁸ are the same or different and represent a hydrogen atom, a halogen atom or an alkyl group having 1 to 10 carbon atoms, and A is an oxygen atom, a sulfur atom or -N
-R ⁹ (wherein R ⁹ represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or an optionally substituted phenyl group), and B is an alkyl group having 1 to 30 carbon atoms or the following formula ( Group represented by III) or (IV)

[Chemical 6] (However, X is a single bond, -O-, -COO-, -OCO.
_{-, - CH 2 O -,} - N = N -, - CH = N- or -
Represents N = CH-, R ¹⁰ represents an alkyl group, an alkoxy group, a halogen atom or a cyano group having 1 to 30 carbon atoms, r is representative of a represents an integer of 1 to 5). ]

The amount of the photochromic compound contained in the above composition varies depending on the desired physical properties, but is preferably in the range of 0.1 to 50% by weight, more preferably 1 to 20% by weight. It is a range. If the amount of the photochromic compound is less than the above range, it is not possible to obtain a change in the physical properties due to the intended photoisomerization, and if it is more than the above range, the liquid crystallinity is significantly reduced,
It becomes difficult to fabricate the cell.

Next, the case of the optical modulator of the second aspect of (2) will be described. In a side chain type polymer liquid crystal having a photochromic component covalently bonded to a side chain, various methods are possible as a method of introducing the photochromic compound into the side chain of the polymer liquid crystal. One of them is a method of copolymerizing a liquid crystal monomer having an addition polymerization property and a photochromic monomer by a usual radical polymerization or an ionic polymerization, and the other one is a method in which a reactive polymer such as reactive silicone is unsaturated. In this method, a liquid crystal compound having a double bond (hereinafter referred to as "reactive liquid crystal compound") and a photochromic compound having a double bond (hereinafter referred to as "reactive photochromic compound") are subjected to an addition reaction. The liquid crystal monomer used in the above copolymerization method is Makromol. Chem. , Vol. 17
9, p273 (1978), Eur. Polym.
J. , Vol. 18, p651 (1982) and Mo.
l. Cryst. Liq. Cryst. , Vol. 16
9, pp167 to 192 (1989) and the like can be used, and examples thereof include biphenyl type, phenylbenzoate type, cyclohexylbenzene type, azoxybenzene type, azomethine type, phenylpyrimidine type, biphenylbenzoate type , Cyclohexylbiphenyl-based, terphenyl-based liquid crystal molecules, and an acrylic acid ester or a methacrylic acid ester bonded via an appropriate alkyl spacer.
Specific examples thereof include those represented by the following general formula (IX), but the present invention is not limited thereto.

[0015]

[Chemical 7] (R ¹¹ represents a hydrogen atom or a methyl group, and X and Y are each a single bond, —O—, —COO—, —OCO.
Represents-, -CH = N- or -N = CH-, and R
¹² represents an alkyl group, an alkoxy group, a carboxyl group, a fluoroalkyl group, a fluoroalkoxy group, a cyano group, a halogen atom or a hydrogen atom, and Φ ¹ and Φ ² are
Each represents the same group as described above, and n is 2 to 30
Represents the integer. )

Examples of the polymerizable photochromic monomer include spiropyran derivatives, spirooxazine derivatives, fulgide derivatives or diarylethene derivatives to which an acrylic acid ester or a methacrylic acid ester is bonded. More specific examples include those represented by the following general formula (X) to general formula (XIII), but the present invention is not limited thereto.

[0017]

[Chemical 8] [In the formula, A is an oxygen atom, a sulfur atom or -NR ²² (wherein R ²² represents a hydrogen atom, a halogen atom, an alkyl group or a phenyl group), and R ^{14 to} R ²¹ are a hydrogen atom and a halogen, respectively. Represents an atom, an alkyl group or a phenyl group, and R ¹³ represents a polymerizable group represented by the following formula (XIV) or (XV).

[Chemical 9] (However, R ³⁵ represents a hydrogen atom or a methyl group,
s represents an integer of 1 to 30. )]

[Chemical 10]

[In the formula, R ¹³ and R ^{23 to} R ³⁴ represent groups in the following two cases (a) and (b).
(A) R ¹³ represents a polymerizable group represented by the above formula (XIV) or (XV), and R ^{23 to} R ³⁴ are each a halogen atom, a hydrogen atom, an alkyl group, an alkoxy group, a nitro group or an alkyl-substituted group. Or (b) at least one of R ^{29 to} R ³⁴ represents a group represented by the following formula: — (CH ₂ ) _{S −1} —OCO—CR ³⁵ ═CH ₂ ( However, R ³⁵ and s have the same meaning as above.) R
^The other groups of ¹³ and R ^{23 to} R ³⁴ each represent a halogen atom, a hydrogen atom, an alkyl group, an alkoxy group, a nitro group or an optionally substituted amino group. )]

Further, as the reactive polymer which can be used when it is synthesized by an addition reaction to the reactive polymer,
A representative example is a silicone polymer having active hydrogen, for example, polyhydrogenated methyl siloxane. It is known that such a silicone polymer having active hydrogen undergoes an addition reaction with a compound having an unsaturated double bond in the presence of a platinum catalyst such as hexachloroplatinum (IV) acid hexahydrate, and has a side chain. As a method for synthesizing a high-molecular liquid crystal, Makromol. Chem. , Rapid
Commun. , 3, p557 (1982) and the like. The reactive liquid crystal compound and reactive photochromic compound that can be used here have the same structure as each liquid crystal molecule or photochromic compound used in the above-mentioned addition polymerization, and instead of an acrylate ester group or a methacrylate ester group. , Those having an unsaturated double bond group introduced therein. Specific examples thereof are shown below, but the present invention is not limited thereto.

Examples of the reactive liquid crystal compound include those represented by the following formula (XVI). CH ₂ = CH (CH ₂₎ in ^{_{n-1 -O-Φ 1 -X}} -Φ 2 -R 12 (XVI) ( ^{wherein, R 12, Φ 1, Φ} 2, X and n are the same meaning as defined above Have.)

Examples of the reactive photochromic compound include compounds represented by the following formulas (XVII) to (XX).

[Chemical 11] [In the formula, R ³⁶ represents-(CH ₂ ) _t-1 -CH = CH ₂ (where t = 1 to 30), and A and R ^{14 to} R ²¹ have the same meanings as described above. ]

[Chemical 12] [In the formula, R ^{23 to} R ³⁴ and R ³⁶ represent groups in the following two cases (a) or (b). (A) R ³⁶ is
_{- (CH 2) t-1} -CH = CH 2 ( provided that, t = 1 to 3
0), R ^{23 to} R ³⁴ are each a halogen atom,
A hydrogen atom, an alkyl group, an alkoxy group, a nitro group or an optionally substituted amino group, or (b) at least one of R ^{29 to} R ³⁴ is-(CH ₂ )
_t-1 —CH═CH ₂ (provided that t = 1 to 30), and the groups other than R ^{23 to} R ³⁴ and R ³⁶ are a halogen atom, a hydrogen atom, an alkyl group, an alkoxy group,
It represents a nitro group or an optionally substituted amino group. )]

Also in the method of introducing the photochromic compound into the polymer side chain as described above, the amount of the introduced photochromic component is the same as in the case of the dispersion system of the aspect (1). That is, the amount of the monomer unit is preferably 0.1 to 50% by weight, more preferably 1 to 20% by weight. When the proportion of the photochromic component is lower than 0.1% by weight, it is impossible to obtain the desired change in physical properties due to photoisomerization, and when it is higher than 50% by weight, liquid crystallinity is remarkably lowered. It becomes difficult to fabricate the cell.

The molecular weight (weight average molecular weight) of the polymer liquid crystal is generally selected from the range of 1,000 to 1,000,000, more preferably 1,000 to 50,000. Further, those having a Tg (glass transition point) of 50 ° C. or less are preferable because they show high modulation efficiency.

In the light modulation element of the present invention, a high molecular weight liquid crystal compound and a photochromic compound are essential components, but as described above, a low molecular weight liquid crystal is used for the purpose of increasing the response speed or expanding the operating temperature range. You can mix them. The amount of the mixture is preferably in the range of 1 to 80% by weight, more preferably 5 to 40, with respect to the side chain type polymer liquid crystal containing the photochromic component or the mixture of the side chain type polymer liquid crystal and the photochromic compound. It is in the range of% by weight. When the content of the low molecular weight liquid crystal is less than 1% by weight, the effect of mixing the low molecular weight liquid crystal hardly appears.
If it exceeds 0% by weight, it becomes impossible to form a film. In addition, various weather resistance stabilizers such as antioxidants represented by hindered amines and hindered phenols may be added for the purpose of improving durability and the like. The amount of these weather-resistant stabilizers added is 0 with respect to the total weight of the side chain type polymer liquid crystal having a photochromic component covalently bonded and a low molecular weight liquid crystal, or the side chain type polymer liquid crystal, a photochromic compound and a low molecular weight liquid crystal. The range of 0.01 to 5% by weight is preferable.

Next, the alignment treatment of the light modulation element material of the present invention will be described. The light modulation element material in the present invention is
A method similar to the alignment treatment in the case of containing a low molecular weight liquid crystal can be applied. That is, a method of using a known alignment film that has been subjected to a rubbing treatment by applying a thin film of PVA, polyimide or the like can be applied. In that case, the orientation of the side-chain polymer liquid crystal is effectively achieved by annealing in a temperature range in which the side-chain polymer liquid crystal shows a liquid crystal phase or by gradually heating after heating to a melting point. .

The present invention is characterized in that the side chain type polymer liquid crystal is twisted and aligned. The twisted orientation means that the orientation directions of the surface of the polymer liquid crystal film are in a twisted relationship with the normal line as an axis, as shown in FIG. At this time, the direction of the alignment vector inside the polymer liquid crystal film changes gently from one alignment direction to the other. The twist angle is preferably in the range of 30 ° to 150 °, more preferably in the range of 60 ° to 120 °.

Next, the structure of the optical modulator of the present invention and the method for manufacturing the same will be described. The light modulation element of the present invention is
It is preferable to have a structure in which the above-mentioned twisted alignment polymer liquid crystal film is sandwiched between at least two substrates. Of course, an alignment film may be provided between the polymer liquid crystal film and the substrate,
A light reflecting layer may be provided on one of the substrates. Furthermore, an antireflection film for preventing reflection on the outermost surface or an interference layer for improving the efficiency of incident laser light may be provided. The thickness of these polymer liquid crystal films is preferably in the range of 0.1 μm to 50 μm, particularly preferably in the range of 1 μm to 20 μm. When an alignment film is provided, its thickness is 0.00
The range of 1 μm to 10 μm is preferable. Examples of the substrate material that can be used here include glass, polycarbonate, polymethylmethacrylate, and olefin resin. In particular, in the case of a transmissive layer structure for reading by transmitted light, the substrate material is preferably transparent.

Next, a typical light modulating element and a method for manufacturing the same will be described. First, a solution containing an alignment film material is applied onto a substrate by a spin coating method, a bar coating method, a doctor blade method, or the like and dried to form an alignment film. This alignment film is rubbed in one direction with a cloth or paper for rubbing. Next, a raw material for forming the polymer liquid crystal film, that is, (1) a side chain type polymer liquid crystal having a covalently bound photochromic component and a low molecular weight liquid crystal optionally added, or (2) a side chain type A liquid crystal comprising a polymer liquid crystal, a photochromic compound, and optionally a low-molecular liquid crystal dissolved in a suitable solvent or heated and melted, and applied on the alignment film to form a polymer liquid crystal film having a predetermined thickness. Form the layers. Another substrate provided with an alignment film is placed on the liquid crystal layer, and pressure bonding under reduced pressure or thermocompression bonding is performed to manufacture a cell. At that time, it is also preferable to obtain a precise film thickness by using a spacer such as fine particles of glass or resin or a film. Finally, it is twisted and oriented by heating it to a predetermined temperature to anneal it or gradually cooling it. The 90 ° twist-oriented cell is transparent, but it can be confirmed by observing with a polarizing microscope that dark and bright states repeatedly appear at every 45 ° rotation angle under parallel Nicols.

Next, a method of performing light modulation using the above light modulator will be described. Light modulation is performed with light having a wavelength: λ _A that the structure A of the photochromic component or photochromic compound has absorption, and wavelength: λ that the structure B has absorption.
Performed by the light of _B, the structure A and B wavelengths no absorption: modulates the linearly polarized light of the lambda _C. That is, after the linearly polarized light is transmitted through the cell or reflected by the cell, the intensity of the light transmitted through the analyzer is modulated. The light modulation method of the light modulation element of the present invention and the configuration thereof will be mainly described in the case of a transmission type. The light modulation element of the present invention can perform light modulation by arranging it between a pair of polarizing plates arranged so that their polarization planes are orthogonal or parallel.
In that case, good optical modulation is performed by arranging the surface of the polymer liquid crystal film in the twisted orientation at an angle of 30 to 60 °, more preferably 45 ° with respect to the polarization plane of the polarizing plate. If a polarized laser is used as the light source for the modulated light, only an analyzer is needed. Even in that case, the orientation direction of the polymer liquid crystal on the device surface is 30 ° to the laser polarization plane.
Good light modulation is achieved by arranging in the range of 60 °, more preferably at an angle of 45 °. In addition to the transmissive type, reflective type readout is also possible.In this case, except for arranging both the polarizing plate and the analyzer on one side of the cell surface so that the polarization planes are orthogonal or parallel, You can do it like a type.

Although the principle of light modulation of the present invention is not clear,
It is assumed as follows. When a side-chain polymer liquid crystal containing at least one photochromic compound is used as the light modulation material in a twisted orientation, the orientation of the portion irradiated with light of wavelength λA changes with the photoisomerization of the forochromic compound. However, the wavelength showing the maximum or minimum of the transmittance changes. If the film thickness is set so that the transmittance is maximized in the initial state, the transmittance of the part irradiated with light of wavelength λA will decrease, while the film thickness will be reduced in the initial state to minimize the transmittance. When is set, the transmittance of the portion irradiated with the light of the wavelength λA increases, so that the transmittance of the light of the wavelength λC can be modulated, and the halftone expression can be realized. Further, by irradiating with light of wavelength λB, it is possible to return to the initial state. In this description, the case where the initial state has maximum or minimum transmittance is described as an example, but the initial state is not limited to this as long as a change in transmitted light is observed before and after photoisomerization. The light modulation element of the present invention is capable of performing light modulation using only light, and is applicable to an optical arithmetic element, an optical memory and the like.

[0031]

EXAMPLES The present invention will be specifically described below with reference to examples. The present invention is not limited to the examples. Example 1 As a side chain type polymer liquid crystal, a liquid crystal having a monomer unit represented by the following structural formula (A) was used. The weight average molecular weight of this polymer liquid crystal was about 6000, and the temperature range showing a liquid crystal phase was 20.1 to 98.8 ° C. The cell was manufactured as follows. First, 8% by weight on two glass substrates
Spin PVA aqueous solution and rub with cotton,
Then, on one of the glass substrates, a 40 wt% tetrahydrofuran (THF) solution of a mixture obtained by adding 5 wt% of fulgide represented by the following structural formula (B) to the above side chain type polymer liquid crystal was applied by a bar coater. . 20μ after drying
m resin spacers were sprinkled, the other glass substrate was stacked so that the rubbing directions were perpendicular to each other, and the temperature was raised to 120 ° C. and pressure bonding was performed. The cell was annealed at 90 ° C. for 1 hour after pressure bonding and twist-oriented. The structure of the cell is shown in FIG. In the figure, 1 is a transparent substrate, 2 is a PVA rubbing film, 3 is a polymer liquid crystal twist-oriented at a twist angle of 90 °, and 4 is a spacer.

[0032]

[Chemical 13] (In the formula, Me represents a methyl group.) The cells thus prepared are transparent and show a good orientation, and when observed by a polarizing microscope, they are in a dark and bright state at every rotation angle of 45 ° under parallel Nicols. Repeatedly appeared. This cell exhibited photochromism upon UV irradiation. Figure 3 shows the absorption spectrum change before and after UV irradiation.
= 365 nm), the maximum absorption was at λ = 520 nm, and the absorption edge was 630 nm. As shown in FIG. 4, the cell 5 was placed between the polarizing plates 6 and 7 under a parallel nicol with the rubbing direction being at an angle of 45 ° with the polarization plane. Fig. 5 shows the change in the transmission spectrum before and after the ultraviolet irradiation when light is vertically incident on the cell (measurement temperature 25
C). 630nm to 83, which is not related to the absorption of fulgide
A maximum change of about 5% in transmitted light appeared in the wavelength region of 0 nm. This change was reversible and could be initialized by irradiation with white light, but no change occurred by irradiation with light λ C (780 nm). Also, it was excellent in repeated stability.

Example 2 Polymerizable fulgide compound represented by the following structural formula (C):
1 g and a liquid crystal single monomer represented by the structural formula (D), 1.9.
g in THF as a solvent and azoisobutyronitrile (AI
BN) was used as an initiator for copolymerization.

[Chemical 14] (In the formula, Me represents a methyl group.) Reprecipitation purification was carried out using methanol to obtain 1.8 g of a polymer liquid crystal as a pale yellow solid. As a result of MNR analysis, the composition was confirmed to be almost the same as the composition at the time of charging. The weight average molecular weight of this polymer liquid crystal was about 6000, and the temperature range showing a liquid crystal phase was 17 to 96.5 ° C. Using this polymer liquid crystal, a cell was prepared in the same manner as in Example 1. After pressure bonding, annealing treatment was performed at 90 ° C. for 1 hour to twist and orient at a twist angle of 90 °. The cell has a maximum absorption at λ = 520 nm upon irradiation with ultraviolet light, and the absorption edge is 630 nm
Met. The change in the transmission spectrum under parallel Nicols is from 630 nm to 8 regardless of the absorption of fulgide.
The maximum expression was about 3% in the wavelength region of 30 nm. This change was reversible and could be initialized by irradiation with white light.
No change occurred by irradiation with light λ C (780 nm).

Example 3 As the side chain type polymer liquid crystal, the one represented by the above structural formula (A) was used. The weight average molecular weight of this side chain type polymer liquid crystal is about 20,000, and the temperature range showing a liquid crystal phase is 35 ° C to 1 ° C.
It was 22 ° C. A 40 wt% THF solution of a mixture of 7% by weight of the fulgide represented by the structural formula (B) and 10% by weight of a nematic liquid crystal (E44, manufactured by Merck Ltd.) was added to the side-chain polymer liquid crystal. After coating with a coater and drying, a cell was prepared in the same manner as in Example 1. After pressure bonding, the cell was annealed at 90 ° C. for 1 hour and twist-oriented at a twist angle of 90 °. The produced cell exhibited maximum absorption at λ = 520 nm upon irradiation with ultraviolet rays and had an absorption edge of 630 nm. The change in transmission spectrum under parallel nicols is 6 regardless of the absorption of fulgide.
The maximum expression was about 7% in the wavelength range of 30 nm to 830 nm. This change was reversible and could be initialized by irradiation with white light, but no change occurred by irradiation with light λ C (780 nm).

Example 4 In the same manner as in Example 2, the polymerizable fulgide compound represented by the structural formula (C) and the liquid crystal monomer represented by the structural formula (D) were mixed in a solvent amount and an initiator amount of 50 mg. The weight average molecular weight of the polymer liquid crystal obtained by polymerization was about 20,000, and the temperature range showing a liquid crystal phase was 33 ° C to 106 ° C. A 40 wt% THF solution of a mixture obtained by adding 10 wt% of nematic liquid crystal (E44, manufactured by Merck & Co., Inc.) to the side chain type polymer liquid crystal at 20 wt% was applied by a bar coater. After drying, a cell was prepared in the same manner as in Example 1. After pressure bonding, the cell was annealed at 90 ° C. for 1 hour and twist-oriented at a twist angle of 90 °. The produced cell exhibited maximum absorption at λ = 520 nm upon irradiation with ultraviolet rays and had an absorption edge of 630 nm. The change in the transmission spectrum under the parallel Nicols was expressed in the wavelength region of 630 nm to 830 nm at a maximum of about 5% regardless of the absorption of fulgide. This change was reversible and could be initialized by irradiation with white light, but no change occurred by irradiation with light λ C (780 nm).

[0036]

The optical modulator of the present invention, as described above,
Since it has a twist-aligned side chain type polymer liquid crystal film containing at least a photochromic component or a photochromic compound, it can reversibly change the transmitted light spectrum by modulating light in a wavelength range where the photochromic compound does not have absorption. it can. Further, the light modulation element of the present invention has high sensitivity, excellent durability and stability, non-destructive readout is possible, and produces a large modulation effect in a wide temperature range. Therefore, the light modulation element of the present invention is
Optical modulation and high-density recording in font mode are possible, and it is useful as an optical arithmetic element, optical sensor, optical disk, optical memory card, and the like.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a twisted orientation of a polymer liquid crystal film.

FIG. 2 is a schematic cross-sectional view of a light modulation element of the present invention.

FIG. 3 is a graph showing a transmitted light spectrum before and after irradiation of ultraviolet light for the light modulation element of Example 1.

FIG. 4 is a schematic diagram of an optical system of a light modulation element.

5 is a transmitted light spectrum before and after ultraviolet irradiation when the light modulation element of Example 1 is installed under a parallel nicol with a rubbing direction at an angle of 45 ° with a polarization plane. FIG.

[Explanation of symbols]

1 ... Transparent substrate, 2 ... PVA rubbing film, 3 ... Twist-oriented polymer liquid crystal, 4 ... Spacer, 5 ... Cell, 6 and 7 ... Polarizing plate.

Claims (6)

[Claims] 1. A light modulation element comprising a polymer liquid crystal film obtained by subjecting a side-chain polymer liquid crystal containing a photochromic compound as one component to a twist alignment treatment. 2. The light modulation element according to claim 1, wherein the side chain type polymer liquid crystal containing a photochromic compound as one component has a photochromic component covalently bonded in the side chain. 3. The light modulation element according to claim 1, wherein the polymer liquid crystal film comprises at least two components of a side chain type polymer liquid crystal having a photochromic component covalently bonded in its side chain and a low molecular weight liquid crystal. 4. The light modulation element according to claim 1, wherein the side chain type polymer liquid crystal containing the photochromic compound as one component comprises a side chain type polymer liquid crystal in which the photochromic compound is dispersed. 5. The light modulation element according to claim 1, wherein the polymer liquid crystal film comprises at least three components of a side chain polymer liquid crystal, a photochromic compound and a low molecular liquid crystal. 6. The light modulation element according to claim 4, wherein the photochromic compound contains at least one kind of a thermostable photochromic compound represented by the following general formula (I) or (II). [Chemical 1] [Wherein R ^{1 to} R ⁸ are the same or different and represent a hydrogen atom, a halogen atom or an alkyl group having 1 to 10 carbon atoms, and A is an oxygen atom, a sulfur atom or -N
-R ⁹ (wherein R ⁹ represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or an optionally substituted phenyl group), and B is an alkyl group having 1 to 30 carbon atoms or the following formula ( A group represented by III) or (IV): (However, X is a single bond, -O-, -COO-, -OCO.
_{-, - CH 2 O -,} - N = N -, - CH = N- or -
Represents N = CH-, R ¹⁰ represents an alkyl group, an alkoxy group, a halogen atom or a cyano group having 1 to 30 carbon atoms, r is representative of a represents an integer of 1 to 5). ]