JP2762863B2 - Optical modulation element and method for reading optical memory using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel light modulation device and a light modulation method using the same, and more particularly, to a stable and high-density optical operation device using a photochromic compound and a rewritable optical memory material. The present invention relates to an optical modulation element that can be used as a device and a reading method of an optical memory using the same.

[0002]

2. Description of the Related Art Heretofore, there have been known light modulation elements utilizing an electro-optic effect, a magneto-optic effect, an acousto-optic effect, and the like. The electro-optic effect utilizes the change in the refractive index due to the application of an electric field, and the magneto-optic effect utilizes the phenomenon that the plane of polarization is rotated by a magnetic field. In the acousto-optic effect, for example, a high-frequency voltage is applied to a transducer formed of a comb-shaped electrode formed on a waveguide to generate a surface acoustic wave according to the frequency of an input signal. Utilizing the phenomenon that the polarization angle of guided light changes due to the interaction of As described above, in the conventional light modulation element, since light modulation is performed by applying an electric field or a magnetic field, there has been a limit to high definition and high speed. Therefore, a device that can perform light modulation using light has attracted attention as a very useful device. As the light modulation element that performs light modulation using the light, (1) a light modulation element combining a photoconductive element and a liquid crystal element, and (2) a light modulation element using a mixture of a ferroelectric liquid crystal and a photochromic compound ( Proceedings of the 17th Meeting of the Japanese Society for Studying Liquid Crystals, p. 246), (3) a light modulation element that orients the transition moment of a photochromic compound in a fixed direction and utilizes the birefringence change of the photochromic compound accompanying photoisomerization (Japanese Unexamined Patent Publication No. No. 190827) has been proposed.

On the other hand, regarding the use of a light modulation element as an optical memory, a method using a photochromic compound as a rewritable optical memory has been conventionally proposed. However, in the conventional method, when reading out the memory, it is necessary to expose the photochromic compound to light in a wavelength range where the photochromic compound has absorption. Since the light used at the time of reading is also the erasing light of the memory, the memory is destroyed. There was a serious problem in practical use. For this reason, a method of using a change in optical rotation at a long wavelength without light absorption as a change other than a change in absorbance of a photochromic compound for reading (Japanese Patent Laid-Open No. 1-24653).
No. 8) and a method in which a refractive index anisotropy is generated and readout is performed using light in a long wavelength region without light absorption (Chemical Society of Japan 58th Spring Meeting 1989 Preliminary Proceedings 31H3)
0) has been proposed. Attempts have been made to obtain even greater changes by combining with a liquid crystal material. For example, a method in which a chiral photochromic compound is mixed with a liquid crystal material and the cholesteric liquid crystal phase is changed by photoisomerization (The 52nd Annual Meeting of the Chemical Society of Japan, 198)
And a method of mixing a liquid crystal material with a compound whose structure changes significantly by a photochromic reaction and using the change in circular dichroism spectrum due to photoisomerization. In addition, in order to prevent deterioration over time due to the liquidity of the liquid crystal, a method of using a polymer liquid crystal as a liquid crystal material, or fixing a photochromic compound on a substrate, and photoisomerizing the photochromic compound on the substrate to form a liquid crystal. There is known a method of changing the orientation state of the compound (Japanese Patent Laid-Open No. 1-251).
344).

[0004]

The above-mentioned cases (1) and (2) essentially utilize the electro-optic effect, and pose a problem of power consumption. In the case of (1), since the photoconductive element and the liquid crystal element are laminated, the process is complicated, and in the case of (2), the structure is simple but the bistable state of the ferroelectric liquid crystal. Therefore, only binary modulation can be performed, and the operating temperature range is narrow.
Further, in the case of (3), there is a problem that a sufficient contrast cannot be obtained because a change in birefringence due to photoisomerization is small. On the other hand, when these conventionally proposed light modulation elements are used as an optical memory, there are various practical problems and they are not sufficient. For example, in a method of reading a change other than absorption of a photochromic compound,
There is a problem that practical use is difficult because the change in optical properties is small. Also, in the method of combining with a liquid crystal material, the liquid crystal flows with the passage of time and the memory becomes unclear, and further, there is a problem in the thermal stability and the repeated durability of the memory. Furthermore, the method using the phase change of the polymer liquid crystal has a problem that it is difficult to completely erase the memory. As described above, conventional memory materials using a photochromic compound have various problems and have not been put to practical use.

Accordingly, the present invention has been made to solve the above-mentioned problems in view of the above-mentioned circumstances of the prior art. An object of the present invention is to provide a light-light modulation element having high density, high sensitivity, excellent stability, and a simple configuration. Another object of the present invention is to provide an optical modulation element used as an optical memory material having excellent nondestructive readability, durability, and stability. Still another object of the present invention is to provide a method for non-destructively reading a memory written in a light modulation element.

[0006]

The present inventors have conducted intensive studies and as a result, have found that in a side-chain type polymer liquid crystal which has been uniaxially oriented, the refraction of a polymer liquid crystal medium induced by a photochromic reaction. It has been found that light in a wavelength range where the photochromic compound has no absorption is modulated by a change in the rate anisotropy. Further, by utilizing this phenomenon, it has been found that a non-destructive readout of a memory with light of a specific wavelength realizes a memory having excellent repeatability, and has completed the present invention.

The light modulation element of the present invention is characterized by comprising a polymer liquid crystal film in which a side chain type polymer liquid crystal containing at least a photochromic compound as one component is uniaxially oriented. Can modulate the light in the wavelength region having no absorption using the change in the refractive index anisotropy of the polymer liquid crystal film caused by the photoisomerization of the photochromic compound. The light modulation device of the present invention includes (A) a polymer liquid crystal film obtained by uniaxially aligning a side-chain polymer liquid crystal having a photochromic component covalently bonded thereto, and (B) a photochromic compound dispersed therein. A liquid crystal polymer film in which a side chain type polymer liquid crystal is uniaxially oriented can be used. The reading method of the optical memory according to the present invention is characterized in that the memory written in the optical modulation element composed of the polymer liquid crystal film of (A) or (B) is subjected to the photochromic component Is read out as a change in the refractive index anisotropy of the polymer liquid crystal medium caused by photoisomerization of the polymer liquid crystal medium.

Hereinafter, the present invention will be described in detail. 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. Is used in which a photochromic compound is bonded to a side chain by a covalent bond. In the case of the polymer liquid crystal film (B), a photochromic compound dispersed in a side chain type polymer liquid crystal is used. You. Here, the side chain type polymer liquid crystal is a polymer having a mesogen molecule exhibiting liquid crystallinity as a pendant in a side chain via a predetermined alkyl spacer, and like a low molecular weight liquid crystal, a nematic phase, a smectic phase or a cholesteric phase. It forms various liquid crystal phases such as phases. Its structure is described in Mol. Cryst. Li
q. Cryst. , Vol. 167, p169 (198
9) and the like.

First, the case of the side chain type polymer liquid crystal (A) having a photochromic component covalently bonded will be described. In the present invention, the side chain type polymer liquid crystal having a covalently bound photochromic component includes a copolymer of a liquid crystal monomer having photopolymerization properties with an addition polymerizable monomer, and a reactive polymer such as a reactive silicone. A polymer obtained by performing an addition reaction of a liquid crystal compound having a bond (hereinafter, referred to as a “reactive liquid crystal compound”) and a photochromic compound having a double bond (hereinafter, referred to as a “reactive photochromic compound”) can be given. .

The above liquid crystal monomer having addition polymerizability is
Makromol. Chem. , Vol. 179, p2
73 (1978), Eur. Polym. J. , Vo
l. 18, p651 (1982) and Mol. Cry
st. Liq. Cryst. , Vol. 169, pp1
67-192 (1989), for example, biphenyl, phenylbenzoate, cyclohexylbenzene, azoxybenzene, azomethine, phenylpyrimidine, biphenylbenzoate, cyclohexylbiphenyl, terphenyl, etc. It has a structure in which an acrylate or a methacrylate is bonded to each liquid crystal molecule via an appropriate alkyl spacer. Specifically,
Examples thereof include those represented by the following general formula (I), but the present invention is not limited thereto.

[0011]

Embedded image [R ¹ represents a hydrogen atom or a methyl group, and X and Y each represent a single bond, -O-, -COO-, -OCO
-, -CH = N- or -N = CH-,
² 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 following groups

[0012]

Embedded image

Embedded image (However, Q represents a hydrogen atom, a fluorine atom, a chlorine atom or a bromine atom, j represents 0 or an integer of 1 to 4), and m represents an integer of 1 to 30. ]

The polymerizable photochromic monomer includes a spiropyran derivative, a spirooxazine derivative, a fulgide derivative, or a diarylethene derivative bonded to an acrylate or methacrylate. More specifically, those represented by the following general formulas (II) to (VII) are exemplified, but the present invention is not limited thereto.

[0014]

Embedded image

[Wherein R ^p represents the following formula;

Embedded image (However, R ¹ represents a hydrogen atom or a methyl group, and n
Represents 0 or an integer of 1 to 30. ), R ³ -R
¹² is a halogen atom, a hydrogen atom, an alkyl group,
Represents an alkoxy group or a nitro group, and R ^{13 to} R ¹⁸ are
Each represents a halogen atom, a hydrogen atom, an alkyl group, an alkoxy group, a nitro group or a group represented by the following formula (VIII) or (IX). However, at least 1 of R ^{13 to} R ¹⁸
When one is a group represented by the following formula (VIII) or (IX), R ^p is a hydrogen atom, an alkyl group, an alkoxy group, and a phenyl group or an aralkyl group which may be substituted. — (CH ₂ ) _n —OCO—CR ¹ ＣＨCH ₂ (VIII) —O— (CH ₂ ) _n —OCO—CR ¹ IXCH ₂ (IX) (where R ¹ and n have the same meaning as described above) .) R
^{19 to} R ³⁴ each represent a halogen atom, a hydrogen atom, an alkyl group, or a phenyl group; A represents an oxygen atom, a sulfur atom, or N—R ^x (where R ^x is a halogen atom,
Represents a hydrogen atom, an alkyl group, or a phenyl group. )
Represents ]

As a typical reactive polymer, a silicone polymer having active hydrogen, for example, polyhydrogenated methylsiloxane can be mentioned. The reactive liquid crystal compound to be subjected to the addition reaction with the reactive polymer has a structure similar to that of the acrylate and methacrylate represented by the general formula (I), but has an unsaturated double bond instead of an acryl or methacryl group. Those having a bond-containing aliphatic group are used. Specific examples thereof include those represented by the following general formula (X), but the present invention is not limited to these. CH ₂ = CH (CH ₂₎ in ^{_{k-2 -O-Φ 1 -X}} -Φ 2 -R 2 (X) ( wherein, k is an integer of from 2 to ^{30, R 2, Φ 1,} Φ 2 and X is Has the same meaning as described above.)

As the reactive photochromic compound to be added to the reactive polymer, compounds represented by the following general formulas (XI) to (XVI) can be mentioned.

[0018]

Embedded image

Wherein R ^r is — (CH ₂ ) _k-2 CH =
CH ₂ (where k = 2 to 30), R ^{3 to} R ¹²
Are each a halogen atom, a hydrogen atom, an alkyl group, an alkoxy group or a nitro group, R ¹⁹ to R ³⁴ are each a halogen atom, a hydrogen atom, an alkyl group or a phenyl group,, R ³⁵ to R ⁴⁰ are, each halogen atom, a hydrogen atom, an alkyl group, an alkoxy group, a nitro group, or _{- (CH 2) k-2} CH = CH 2 ( provided that, k =. 2 to
30), provided that any one of R ^{35 to} R ⁴⁰ represents — (CH ₂ ) _k-2 CH = CH ₂ , wherein R ^r represents a hydrogen atom, an alkyl group, an alkoxy group, and A represents an oxygen atom, a sulfur atom or N—R ^x (where R ^x represents a halogen atom, a hydrogen atom, an alkyl group or a phenyl group), and R ^r represents a phenyl group or an aralkyl group. _{, - (CH 2) k-} 2 CH = CH
₂ (where k = 2 to 30). ]

Next, a method for producing a side chain type polymer liquid crystal having a covalently bound photochromic component of the present invention will be described. Various methods can be adopted for introducing the photochromic component. As one of the methods, there is a method of copolymerizing the above-mentioned liquid crystal monomer having addition polymerizability and a photochromic monomer by ordinary radical polymerization or ionic polymerization. As still another example, the reactive liquid crystal compound and the reactive photochromic compound are added to a reactive polymer, for example, polyhydrogenated methylsiloxane using a platinum catalyst such as hexacycloloplatinate (IV) acid hexahydrate. A method of reacting is mentioned.

In the present invention, the photochromic component to be introduced is preferably in the range of 0.1 to 50% by weight, more preferably in the range of 1 to 20% by weight in monomer units. If the ratio of the photochromic component is lower than 0.1% by weight, the desired change in physical properties due to photoisomerization cannot be obtained. If the ratio is higher than 50% by weight, the liquid crystallinity is significantly reduced, It becomes difficult to manufacture a cell used as an optical memory material or the like.

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

Next, the case of the side chain type polymer liquid crystal in which the photochromic compound (B) is dispersed will be described. The structure of the side chain type polymer liquid crystal used is described in Mol. Cryst. Liq. Cryst. , 16
7, 169 (1989). For example, positive dielectric anisotropy cyanobiphenyl, cyanophenylbenzoate, cyanobiphenylbenzoate, cyanophenyl (4-phenylbenzoate), or
Methoxy biphenyl, methoxy phenyl benzoate, methoxy biphenyl benzoate having a negative dielectric anisotropy,
Those having a methoxyphenyl (4-phenylbenzoate) structure and having a main chain structure of polyacrylate, polymethacryl, polyether, polyester, polysiloxane and the like can be generally used. Specific examples thereof include those composed of monomer units represented by the following general formulas (XVII) to (XX), but are not limited thereto.

[0024]

Embedded image (Wherein, p represents an integer of 1 to 20, and R ¹ , R ² ,
X, Y, m, Φ ¹ , Φ ² and Q each have the same meaning as described above. )

The photochromic compound dispersed in the side chain type polymer liquid crystal is described in US Pat. H. Brown
Various compounds described in "Photochromism" can be mentioned. Examples include spiropyran derivatives, spirooxazine derivatives, azobenzene derivatives, fulgide derivatives, diarylethene derivatives, triarylmethane derivatives, and indigo derivatives. In particular, fulgide derivatives and diarylethene derivatives, which are photon mode photochromic compounds that do not cause thermal isomerization, are preferably used from the viewpoint of improving the stability of the memory when used as an optical memory. Examples of the fulgide derivative and diarylethene derivative used include compounds represented by the following general formulas (XXI) to (XXVI).

[0026]

Embedded image

[0027] [In the formula, A, oxygen atom, sulfur atom or ^{N-R x,} B represents an oxygen atom or ^{N-R x,} (provided that, ^{R x} is a halogen atom, a hydrogen atom, an alkyl group Or represents a phenyl group which may be substituted.), R ^{19 to} R ³⁴ , R ⁴¹ and R ⁴² represent a halogen atom, a hydrogen atom, an alkyl group or a phenyl group which may be substituted. The amount of the photochromic compound contained in the composition may vary depending on the desired physical properties, but is preferably in the range of 0.1 to 50% by weight, more preferably in the range of 1 to 20% by weight. is there.
If it is less than the above range, it is not possible to obtain a change in physical properties due to the intended photoisomerization, and if it is more than the above range, the liquid crystallinity is significantly reduced, and it is difficult to produce a cell such as an optical memory material. Become.

The light modulating element of the present invention is a polymer liquid crystal uniaxially oriented comprising the above-mentioned side chain type polymer liquid crystal having a covalently bound photochromic component or a side chain type polymer liquid crystal in which a photochromic compound is dispersed. Although these films are made of a film, these light modulators may further contain various weathering stabilizers such as antioxidants represented by hindered amines and hindered phenols for the purpose of improving durability and the like. The amount of these weathering stabilizers added is a side-chain type polymer liquid crystal having a photochromic component covalently bonded,
Alternatively, the content is preferably in the range of 0.01 to 5% by weight based on the total weight of the side chain type polymer liquid crystal and the photochromic compound.

Further, the light modulation element of the present invention includes:
A low-molecular liquid crystal material may be mixed for the purpose of increasing the change in physical properties due to photoisomerization to increase the response speed or extend the operating temperature range. As a result, the effect of lowering the viscosity and improving the change in the refractive index anisotropy occurs. The amount of these additives is preferably in the range of 1 to 80% by weight based on the total amount of the side chain type polymer liquid crystal having a covalently bound photochromic component, or the total amount of the side chain type polymer liquid crystal and the photochromic compound.
More preferably, it is in the range of 10 to 40% by weight. If it is lower than this range, the effect of mixing the low-molecular liquid crystal material hardly appears, and if it is higher than the above range,
Film formation cannot be performed.

Next, a description will be given of the orientation treatment of the light modulation element material composed of the above-mentioned materials. The same method as the alignment treatment in the case of including a low-molecular liquid crystal can be applied to the light modulation element material in the present invention. That is, a method using a known alignment film which has been subjected to a rubbing treatment by applying a thin film such as PVA or polyimide can be applied. In this case, the orientation of the side-chain type polymer liquid crystal is effectively achieved by annealing in a temperature range where the side-chain type polymer liquid crystal exhibits a liquid crystal phase, or by gradually cooling after heating to the melting point. . Further, a method peculiar to the polymer liquid crystal in which the polymer liquid crystal film is aligned by an external stress such as a stretching treatment without using the alignment film is also preferably applicable.

Next, the configuration of the light modulation element of the present invention and a method of manufacturing the same will be described. The light modulation element is a polymer liquid crystal film composed of a side chain polymer liquid crystal having a photochromic component covalently bonded between at least two substrates, or a polymer liquid crystal film composed of a side chain polymer liquid crystal in which a photochromic compound is dispersed. Those having a structure in which a film is sandwiched are preferable. Of course, an alignment film may be provided between the polymer liquid crystal film and the substrate, and a light reflection layer may be provided on one of the substrates.
Further, an antireflection film for preventing reflection on the outermost surface and an interference layer for improving the efficiency of incident laser light may be provided. The thickness of these polymer liquid crystal films is 0.1 μm to 50 μm.
μm is preferable, and 1 μm to 20 μm is particularly preferable.
m. When an alignment film is provided, the thickness is preferably in the range of 0.001 μm to 10 μm. Examples of the substrate material that can be used here include glass, polycarbonate, polymethyl methacrylate, and an olefin-based resin. In particular, in those having a transmission-type layer configuration in which reading is performed using transmitted light, the substrate material is preferably transparent. FIG. 2 shows an example of the light modulation element of the present invention. In the figure, 1 is a transparent substrate, and 2 is PVA.
The rubbing film 3 is a uniaxially oriented polymer liquid crystal, and 4 is a spacer.

Next, a representative light modulation element and a method for manufacturing the same will be described. First, a solution containing an alignment film material is applied on 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 by rubbing in one direction using cloth or paper. Next, the raw material for forming the polymer liquid crystal film is dissolved or heated and melted in a suitable solvent, and applied on the alignment film to form a liquid crystal layer having a predetermined thickness. I do. Another cell provided with an alignment film on the liquid crystal layer is stacked, and pressure-bonding under reduced pressure or heat-pressure bonding is performed to manufacture a cell. At this time, it is also preferable to obtain an accurate film thickness using a spacer such as glass or resin fine particles or a film.
Finally, the liquid crystal is aligned in a uniaxial direction by heating to a predetermined temperature and performing an annealing process, or by gradually cooling. Uniaxially oriented cells are transparent, but have birefringence, and when observed with a polarizing microscope, dark and bright states appear repeatedly at every 45 ° rotation angle under crossed Nicols,
The orientation can be confirmed.

Next, a method of performing light modulation using the above-described light modulation element will be described. The light modulation is performed by the light having a wavelength: λ _A in which the structure A of the photochromic component or the photochromic compound has absorption, and the wavelength in which the structure B has absorption: λ.
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, the linearly polarized light passes through the cell or is reflected by the cell and then passes through the analyzer, but the intensity of the light is modulated. The light modulation method and the configuration thereof, which are features of the present invention, will be described mainly for a transmission type. The light modulation element of the present invention can perform light modulation by being arranged between a pair of polarizing plates arranged so that the polarization planes are orthogonal or parallel.
In this case, the alignment direction of the polymer liquid crystal is 30
By arranging at an angle in the range of ６０60 °, more preferably 45 °, good light modulation is performed. When a polarized laser is used as the light source of the modulated light, only the analyzer is required. Also in this case, by arranging the polymer liquid crystal film at an angle in the range of 30 ° to 60 °, more preferably 45 ° with respect to the laser polarization plane, good light modulation is performed. When the light modulation element is a reflection type, it may be performed in the same manner as the transmission type, except that both the polarizer and the analyzer are arranged on one side of the cell surface so that the polarization planes thereof are perpendicular or parallel. .

The light modulation element of the present invention can be used as an optical memory material. Writing and reading when the structure of the photochromic component or the photochromic compound in the case where the memory is not used is A and the structure where the memory is the memory is B is used as the optical memory material will be described. Writing is performed by light having a wavelength: λ _A at which the structure A of the photochromic component or the photochromic compound has absorption, and is changed to the structure B and stored. The readout is performed using linearly polarized light at a wavelength: λ _C where Structure A and Structure B have no absorption, and as the difference in the intensity of the light transmitted through the analyzer after this linearly polarized light has passed or reflected the cell. Is read. Erasing is realized by irradiating light having a wavelength: λ _{B at} which structure B has absorption to change to structure A.

Next, a non-destructive read method according to the present invention will be described. When the light modulation element is of the transmission type, the information (spot) recorded on the optical memory material is:
Reading can be performed by disposing the polarizing plane between two polarizing plates (one is a polarizer and the other is an analyzer) arranged in a perpendicular (crossed Nicols) or parallel (parallel Nicols). . In this case, good readout is realized by arranging the orientation direction of the polymer liquid crystal film at an angle of 30 ° to 60 °, more preferably 45 °, with the polarization plane of the polarizer. When a polarized laser is used as the light source of the reading light, only the analyzer is required. Also in this case, the alignment direction of the polymer liquid crystal film is 30 ° with respect to the laser polarization plane.
By arranging at an angle in the range of ６０60 °, more preferably 45 °, good readout is realized. Further, when the light modulation element is of a reflection type, it is performed in the same manner as in the transmission type except that both the polarizer and the analyzer are arranged on one side of the cell surface so that their polarization planes are perpendicular or parallel. I just need.

Although the principle of light modulation of the present invention is not clear,
It is assumed as follows. This will be described with reference to FIG. 1 showing reading of an optical memory. In FIG. 1, the solid line and the dotted line indicate the wavelength dependence of the transmittance Tc (or Tp) before and after photoisomerization when the arrangement of the two polarizing plates is crossed Nicols (or parallel Nicols). . The solid line is before photoisomerization and the dotted line is after photoisomerization. When linearly polarized light λ is incident on a birefringent medium having a refractive index anisotropy (△ n), light propagates in such a manner that its polarization direction forms a spiral due to the optical path difference between normal light and extraordinary light. At this time, when the polarization direction of the incident light and the direction of the anisotropy Δn of the refractive index form an angle of 45 °, the intensity of the normal light and the intensity of the extraordinary light become equal. The thickness of the medium having the refractive index anisotropy Δn is d, this medium is sandwiched between two polarizing plates, and the polarization direction of the polarizing plate on the incident side and the direction of Δn take an angle of 45 °. Suppose. At this time, △ nd corresponds to the optical path difference. Assuming that the transmitted light intensity of the first polarizing plate is 1, the transmittance Tc when the arrangement of the two polarizing plates is crossed Nicols is
It is given by equation (1). Tc = sin ² (π △ nd / λ) (1) Further, the transmittance Tp when the two polarizing plates are arranged in parallel Nicols is given by equation (2). Tp = cos ² (π △ nd / λ) (2)

That is, under crossed Nicols, △ nd / λ =
In the case of 0, 1, 2,..., The transmittance is minimized , and △ nd / λ
= 1/2, 3/2..., The transmittance becomes maximum . Further, under parallel Nicol, △ nd / λ = 1/2, 3 /
In the case of 2,..., The transmittance becomes minimum , and △ nd / λ = 0,
In the case of 1, 2,..., The transmittance becomes maximum . Therefore, by selecting an appropriate optical path difference Δnd, the initial transmittance of the modulated light can be set to the maximum or minimum. When used in the thermally containing stable one or more at least a photochromic component or photochromic compound side chain type polymer liquid crystal as an optical modulation element uniaxially oriented, the portion was irradiated with light of wavelength lambda _A is photochromic component Alternatively, Δn changes because the alignment state of the liquid crystal changes due to photoisomerization of the photochromic compound, and the wavelength showing the maximum or minimum transmittance changes (see FIG. 1). For this reason, when the film thickness d is set so that the transmittance in the initial state is minimized, the transmittance of the portion irradiated with the light of the wavelength λ _A increases, so that the transmittance of the light of the wavelength λ _C is modulated. And halftone expression is also possible. In addition, by irradiating light of the wavelength λ _B , it is possible to return to the initial state. In this description, the case where the initial state has the maximum or minimum transmittance is described as an example, but the initial state is not limited to this if a change in transmitted light is observed before and after photoisomerization. .

When the optical modulator of the present invention is used as an optical memory, by selecting an appropriate optical path difference Δnd, the transmittance at the wavelength at which the memory is read in the initial state before recording is written can be maximized or minimized. Can be set. When a side-chain type polymer liquid crystal containing at least one kind of thermally stable photochromic component or photochromic compound is used as an optical memory material in a uniaxial orientation, the portion where the memory is written is a photochromic component or a photochromic compound. The photoisomerization changes the orientation state of the side-chain type polymer liquid crystal, and changes Δn, thereby changing the wavelength indicating the maximum or minimum transmittance (see FIG. 1). For this reason, when the film thickness d is set so that the transmittance in the initial state is minimized, the transmittance of the portion where data has been written to the memory increases, so that recording can be read as a change in the transmittance. This change in transmittance can be reversibly generated with photoisomerization.

[0039]

The present invention will be described below in detail with reference to examples. The present invention is not limited to the embodiments.

Example 1 As a polymer liquid crystal, a side chain polymer liquid crystal composed of a monomer unit represented by the following structural formula (A) was used. The weight average molecular weight of this high-molecular liquid crystal is about 30,000, and the temperature range showing the liquid crystal phase is 35 ° C to 122 ° C. First, an 8% by weight PVA aqueous solution was applied on two glass substrates by spin coating, and then rubbed with cotton. Next, a 40% by weight THF solution obtained by mixing furyl fulgide represented by the following structural formula (B) at a concentration of 5% by weight with the above polymer liquid crystal was applied to one glass substrate using a bar coater. After drying, a resin spacer of 10 μm was sprayed, another glass substrate was overlaid, and the temperature was raised to 130 ° C. and pressure bonded. The cell formed by crimping is 100
Annealing was performed at 30 ° C. for 30 minutes to uniaxially orient. The cell thus produced was transparent and showed good orientation. Further, when observed with a polarizing microscope, dark and bright states repeatedly appeared at 45 ° rotation angles under crossed Nicols.

[0041]

Embedded image (In the formula, Me represents a methyl group.)

The writing to the memory was performed with ultraviolet rays, and the transmitted light before and after irradiation was measured. FIG. 3 shows the change in the absorption spectrum before and after the irradiation of the ultraviolet rays.
nm), shows maximum absorption at λ = 510 nm,
The absorption edge was at 620 nm. Erasing of the memory was realized by using white light, and repeated coloring and erasing were possible by alternately irradiating ultraviolet light and white light. In FIG. 4, under crossed Nicols, the alignment direction is set to 45 degrees with the polarization plane.
The change of the transmission spectrum before and after the irradiation of ultraviolet rays when installed at an angle of ° is shown (measuring temperature 25 ° C). FIG. 5 shows a difference spectrum obtained by subtracting a spectrum before isomerization from a spectrum after isomerization. 630nm not related to fulgide absorption
A change in transmitted light of about 10% occurred in a wavelength region of 830 nm. This change was reversible and could be erased by irradiation with white light, but no erasure of the memory by irradiation with readout light (λ = 780 nm).

Example 2 0.1 g of a polymerizable spirooxazine compound represented by the following structural formula (C) and 1.9 g of a liquid crystal monomer represented by the following structural formula (D) were prepared by using azoisobutyro with THF as a solvent. The copolymer was copolymerized using nitrile (AIBN) as an initiator. The polymer liquid crystal obtained by reprecipitation purification using methanol was a pale red solid (1.8 g), and its composition was N
From the MR analysis, it was confirmed that the composition was almost the same as the composition at the time of preparation. Using the obtained polymer liquid crystal, a cell was produced in the same manner as in Example 1. The weight average molecular weight of this polymer liquid crystal is about 20,000, and the temperature range at which the liquid crystal phase is exhibited is 3
0 ° C to 90 ° C. 3 at 95 ℃ to 1 ℃ / min after crimping
The material was gradually cooled to 5 ° C. to be uniaxially oriented.

[0044]

Embedded image (In the formula, Me represents a methyl group.) As in Example 1, the change before and after the irradiation of ultraviolet rays was measured. It shows maximum absorption at λ = 610 nm by irradiation of ultraviolet rays, and the absorption edge is 700 n.
m. This change was reversible and was erasable by irradiation with white light. Ultraviolet light and white light were emitted every 5 minutes, and the durability was repeatedly evaluated. The results are shown in FIG. 6 (under parallel Nicols, the angle 45 between the orientation direction and the polarization plane).
°, measurement wavelength λ = 760 nm, measurement temperature 25 ° C.). As is apparent from the figure, the polymer liquid crystal in which the spirooxazine component was copolymerized in part of the side chain was excellent in repeated durability, and no deterioration was observed.

Example 3 A polymerizable fulgide compound represented by the following structural formula (E):
0.1 g and 1.9 g of a liquid crystal monomer represented by the following structural formula (F) were copolymerized in the same manner as in Example 2 to synthesize a polymer liquid crystal containing 5% by weight of fulgide as a monomer unit (1.7 g). . The weight average molecular weight of this polymer liquid crystal is about 1
At 8,000, the temperature range at which the liquid crystal phase is exhibited is 33 ° C. to 106 ° C.
° C. A cell was manufactured in the same manner as in Example 1.
By annealing at 100 ° C for 30 minutes after pressing,
Uniaxially oriented. The change before and after the irradiation of the ultraviolet rays was measured in the same manner as in Example 1 (measuring temperature: 25 ° C.). UV irradiation shows maximum absorption at λ = 520 nm, and the absorption edge is 630 n.
m. In the wavelength region from 640 nm to 830 nm, which is not related to the absorption of fulgide, a change in transmitted light of about 10% at the maximum occurred. This change was reversible and could be erased by irradiation with white light, but the memory was not erased by irradiation with read light (λ = 780 nm).

Embedded image (In the formula, Me represents a methyl group.)

Example 4 0.1 g of a polymerizable spirooxazine compound represented by the following structural formula (C) and 1.9 g of a liquid crystal monomer represented by the following structural formula (D) were prepared by using azoisoisopropane in tetrahydrofuran (THF) as a solvent. Copolymerization was performed using butyronitrile (AIBN) as the initiator.

Embedded image (In the formula, Me represents a methyl group.) By reprecipitation purification using methanol, 1.8 g of a polymer liquid crystal was obtained as a pale red solid. Its composition is determined by NMR analysis.
It was confirmed that the composition was almost the same as that in the preparation. The weight average molecular weight of this polymer liquid crystal is about 6,000,
The temperature range showing the liquid crystal phase was 10 to 75 ° C. First, an 8% by weight PVA aqueous solution was spin-coated on two glass substrates and rubbed with cotton. Next, on one glass substrate, 40 wt% T of the above polymer liquid crystal was applied.
The HF solution was applied with a bar coater. After drying, 1
A resin spacer of 0 μm was sprinkled, the other glass substrate was overlaid, the temperature was raised to 120 ° C., and pressure bonding was performed. After the pressure bonding, the cell was annealed at 70 ° C. for 30 minutes to be uniaxially oriented. The resulting cell has the structure shown in FIG. The cell thus produced was transparent and showed good orientation, and when observed with a polarizing microscope, dark and bright states repeatedly appeared at 45 ° rotation angles under crossed Nicols.

This cell exhibited photochromism upon irradiation with ultraviolet light. FIG. 7 shows the absorption before and after ultraviolet irradiation. Irradiation of ultraviolet rays (λ = 365 nm) results in λ = 610
The maximum absorption was shown at nm, and the absorption edge was at 700 nm. The above cell was arranged as shown in FIG. 8 and light was incident thereon. That is, under crossed Nicols, the alignment direction was set at an angle of 45 ° with respect to the polarization planes of the polarizing plates 6 and 7, and light was incident on the cell 5 vertically. In that case, the change in the transmission spectrum before and after the irradiation of ultraviolet rays was investigated (measuring temperature 25 ° C.). FIG. 9 shows the result. 7 not related to spirooxazine absorption
A change in transmitted light of about 6% at maximum occurred in the wavelength region of 00 nm to 830 nm. This change was reversible and could be initialized by irradiation with white light, but did not change by irradiation with light λ _C (780 nm). In addition, the response time defined as the time required to change from 10% to 90% of the variation of the transmitted light intensity of the light λ _C is also 300 times in the decoloring process.
ms and high repetition stability.

Example 5 In the same manner as in Example 4, the polymerizable spirooxazine compound represented by the above structural formula (C) and the liquid crystal monomer represented by the above structural formula (D) were copolymerized by changing the amounts of the solvent and the initiator. Polymerization was performed. The weight average molecular weight of the obtained polymer liquid crystal was about 20,000, and the temperature range in which the liquid crystal phase was exhibited was 30 to 95 °. Using this polymer liquid crystal, a cell was fabricated in the same manner as in Example 4. The cell was uniaxially oriented by annealing at 90 ° C. for 30 minutes after the pressure bonding. The cell was transparent and showed good orientation, and when observed with a polarizing microscope, dark and light states repeatedly appeared at 45 ° rotation angles under crossed Nicols. The change in transmitted light intensity before and after ultraviolet irradiation under crossed Nicols was measured in the same manner as in Example 4, and it was found that the change was from 700 nm to 830 nm which was not related to spirooxazine absorption.
, A change in transmitted light of about 3% at the maximum occurred, and the response time was 700 ms during the decoloring process.

Example 6 As a side chain type polymer liquid crystal, one having a monomer unit represented by the following structural formula (A) (having a weight average molecular weight of about 5,500,
The liquid crystal phase had a temperature range of 15 to 100 ° C.). A 40% by weight THF solution of a polymer liquid crystal obtained by mixing spirooxazine represented by the following structural formula (G) at a concentration of 3% by weight was applied to the side chain type polymer liquid crystal with a bar coater. After drying in the same manner, a 10 μm resin spacer was sprayed, and the other glass substrate was overlaid and pressed. After the pressure bonding, the cell was annealed at 90 ° C. for 30 minutes for uniaxial orientation. The cell was transparent and showed good orientation, and when observed with a polarizing microscope, dark and light states repeatedly appeared at 45 ° rotation angles under crossed Nicols.

Embedded image (In the formula, Me represents a methyl group.) When the change in transmitted light intensity before and after ultraviolet irradiation under crossed Nicols was measured in the same manner as in Example 4, the wavelength region from 700 nm to 830 nm not related to spirooxazine absorption was measured. A change in transmitted light of up to about 7% occurred. 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). In addition, the response time was as fast as 280 ms in the decoloring process, and the repetition stability was excellent.

Example 7 Similar to Example 6, a side chain type polymer liquid crystal comprising the monomer unit represented by the structural formula (A) (having a weight average molecular weight of about 18
000, and the temperature range showing the liquid crystal phase was 35 to 122 ° C). A 40% by weight THF solution of a polymer liquid crystal obtained by mixing spirooxazine represented by the above structural formula (G) at a concentration of 3% by weight was applied to the side chain type polymer liquid crystal by a bar coater. After drying in the same manner, 10 μm
Was spread, and the other glass substrate was overlaid and pressed. After the pressure bonding, the cell was annealed at 90 ° C. for 30 minutes for uniaxial orientation. The cell was transparent and showed good orientation, and when observed with a polarizing microscope, dark and light states repeatedly appeared at 45 ° rotation angles under crossed Nicols. The change in transmitted light intensity before and after ultraviolet irradiation under crossed Nicols was measured in the same manner as in Example 4, and it was found that the change was from 700 nm to 830 nm which was not related to spirooxazine absorption.
, A change in transmitted light of about 4% at maximum occurred.
The response time was 650 ms during the decoloring process, which was slower than the case of Example 3.

Example 8 Polymerizable fulgide compound represented by the following structural formula (E)
1 g and a liquid crystal monomer 1.9 represented by the following structural formula (F)
g was copolymerized using THF as a solvent and AIBN as an initiator. By reprecipitation purification using methanol, 1.7 g of a polymer liquid crystal was obtained as an ocher solid. The composition was confirmed by NMR analysis to be substantially the same as the composition at the time of preparation. The weight average molecular weight of this polymer liquid crystal is about 6,000, and the temperature range at which the liquid crystal phase is shown is 17
９６96.5 ° C.

Embedded image (In the formula, Me represents a methyl group.) A cell was prepared in the same manner as in Example 4 using this high-molecular liquid crystal. After the pressure bonding, the cell was annealed at 90 ° C. for 30 minutes for uniaxial orientation. The cells are transparent, show good orientation,
When observed with a polarizing microscope, the rotation angle is 45 ° under crossed Nicols
In each case, dark and light states repeatedly appeared. This cell exhibited photochromism and exhibited the spectral change shown in FIG. UV irradiation showed maximum absorption at λ = 520 nm, and the absorption edge was 630 nm. Regarding the change in the transmission spectrum under crossed Nicols, a change in the transmitted light of about 15% at the maximum in the wavelength region from 630 nm to 830 nm, which is not related to the absorption of fulgide, appeared. This change was reversible and could be initialized by irradiation with white light, but no change occurred by irradiation with light λC (780 nm).

Example 9 A polymer liquid crystal represented by the following structural formula (H) was used. This polymer liquid crystal has a weight average molecular weight of about 6,0.
00, and the temperature range for displaying the liquid crystal layer is 12.5 to 98 ° C.
Met. First, an 8 wt% PVA aqueous solution was spin-coated on two glass substrates and rubbed with cotton to form a PVA rubbing film. Next, a fulgide compound represented by the following structural formula (B) was mixed with a polymer liquid crystal at a concentration of 3% by weight on one glass substrate.
A weight% THF solution was applied with a bar coater. After drying, a 10 μm resin spacer was sprayed, the other glass substrate was overlaid, the temperature was raised to 130 ° C., and pressure bonding was performed. After the pressure bonding, the cell was annealed at 90 ° C. for 30 minutes for uniaxial orientation. The obtained cell was transparent and showed good orientation. When observed with a polarizing microscope, the cell had a rotation angle of 4 under crossed Nicols.
Dark and light states repeatedly appeared every 5 °.

Embedded image (In the formula, Me represents a methyl group.) This cell exhibited photochromism upon irradiation with ultraviolet light. UV (λ =
(365 nm), the maximum absorption was exhibited at λ = 510 nm, and the absorption edge was 620 nm. FIG. 11 shows the absorption before and after ultraviolet irradiation. The above cell was placed under crossed Nicols at an orientation direction of 45 ° with respect to the plane of polarization, and light was perpendicularly incident on the cell. In that case, the change in the transmission spectrum before and after the irradiation of ultraviolet rays was investigated (measuring temperature 25 ° C.).
FIG. 12 shows the result. In the wavelength range of 620 nm to 830 nm, which is not related to the absorption of fulgide, a change in transmitted light of about 10% at the maximum was developed. This change was reversible and could be initialized by irradiation with white light, but the light λ _C (78
0 nm) irradiation did not change.

[0053]

The light modulation device of the present invention can perform light modulation using only light, and can be applied to an optical operation device, an optical memory, and the like. Further, when the light modulation element of the present invention is used as a memory material, it has excellent non-destructive readability, repetitive durability, and thermal stability of the memory. The reading method has an excellent effect that high-density recording in the font mode is possible and that nondestructive reading, which has been a problem in the past, can be realized. Therefore, the optical memory material of the present invention and the reading method of the present invention are useful and applicable to optical disks, optical memory cards, and the like.

[Brief description of the drawings]

FIG. 1 is a graph illustrating the principle of a reading method according to the present invention.

FIG. 2 is a schematic sectional view of a light modulation device of the present invention.

FIG. 3 is a graph showing transmitted light spectra before and after irradiation of the light modulation element of Example 1 when irradiation with ultraviolet light is performed.

FIG. 4 is a transmission light spectrum before and after ultraviolet irradiation when the orientation direction is set at an angle of 45 ° with respect to a polarization plane under crossed Nicols for the light modulation element of Example 1.

FIG. 5 is a graph showing a difference spectrum of transmitted light before and after irradiation when the light modulation element of Example 1 is irradiated with ultraviolet light under crossed Nicols.

FIG. 6 is a graph showing a change in transmitted light when recording and erasing are performed alternately under parallel Nicols for the light modulation element of Example 2.

FIG. 7 is a graph showing transmitted light spectra before and after irradiation of the light modulation element of Example 4 when irradiation with ultraviolet light is performed.

FIG. 8 is a schematic diagram of an optical system of a light modulation element.

FIG. 9 is a transmission light spectrum before and after ultraviolet irradiation when the orientation direction is set at an angle of 45 ° with respect to the polarization plane under crossed Nicols for the light modulation element of Example 4.

FIG. 10 is a graph showing transmitted light spectra before and after irradiation of the light modulation element of Example 8 when ultraviolet irradiation is performed.

FIG. 11 is a graph showing transmitted light spectra before and after irradiation of the light modulation element of Example 9 when irradiation with ultraviolet light is performed.

FIG. 12 is a transmission light spectrum before and after ultraviolet irradiation when the orientation direction is set at an angle of 45 ° with respect to the polarization plane under crossed Nicols for the light modulation element of Example 9;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2 ... PVA rubbing film, 3 ... Uniaxially oriented polymer liquid crystal, 4 ... Spacer, 5 ... Cell, 6 and 7 ... Polarizing plate.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1333 G02F 1/13 500-505 G03C 1/73 503

Claims (4)

(57) [Claims] 1. A light in a wavelength region in which a photochromic compound has no absorption, comprising a polymer liquid crystal film in which a side chain type polymer liquid crystal containing at least a photochromic compound as one component is uniaxially oriented. A light modulation device that modulates the temperature using a change in the refractive index anisotropy of a polymer liquid crystal film caused by photoisomerization of a photochromic compound. 2. The light modulation device 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 having a covalently bound photochromic component. 3. A photochromic compound comprising a polymer liquid crystal film in which a side-chain type polymer liquid crystal in which a photochromic compound is dispersed is uniaxially oriented, and the light in a wavelength region where the photochromic compound has no absorption is converted into a photochromic compound. A light modulation element that modulates using a change in the refractive index anisotropy of a polymer liquid crystal film caused by photoisomerization. 4. A memory written in a light modulating element comprising a polymer liquid crystal film in which a side chain type polymer liquid crystal containing at least a photochromic compound as one component is uniaxially oriented, and the photochromic component has no absorption. A method for reading out an optical memory, comprising reading out a change in refractive index anisotropy of a polymer liquid crystal medium caused by photoisomerization of a photochromic component by light in a wavelength region.