JPH08146391A - Optical switching method - Google Patents

Abstract

PURPOSE: To provide a polymer liquid crystal having more high-speed responsivity than heretofore by utilizing the change in retardation induced with the photoisomerization due to light irradiation of a layer consisting of a polymer liquid crystal compound that contains mesogen groups having photochromism as its side chains. CONSTITUTION: In this method, the side chains of a polymer liquid crystal are mesogen groups each having a photochromic structure and the polymer liquid crystal shows a liquid crystal phase when the mesogen groups are of trans type. At the time of using such a polymer liquid crystal compound, by irradiating the molecules of the polymer liquid crystal compound oriented on a substrate with light 1 to cause photoisomerization of the mesogen groups from trans to cis type, a phase transition from the liquid crystal phase to an isotropic phase of the polymer liquid crystal compound occurs and thereby, a change in retardation is effected because of the differences of optical properties between the liquid crystal phase and the isotropic phase. By utilizing this change in retardation, the transmission and cutoff of light 2 can be controlled. Since each of the side chains of the polymer liquid crystal compound has a combination of a liquid crystal molecular structure and a photochromic molecular structure, the photoisomerization of each of the molecules of the polymer liquid crystal compound and the liquid crystal phase transition are concurrently induced and the whole system is simultaneously changed to obtain high-speed responsivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel liquid crystal optical element utilizing the change in the alignment of liquid crystal due to the action of light, and more specifically, it provides photochromism on a transparent substrate having a polarizing plate and an alignment film. A liquid crystal composition containing a polymer liquid crystal compound having a mesogenic group shown in the side chain or a thin film layer of a polymer liquid crystal compound having a mesogenic group showing photochromism as a side chain is provided, and reading light is switched by writing light. The present invention relates to a liquid crystal optical element and an optical information recording medium that can be used.

[0002]

2. Description of the Related Art As a liquid crystal optical element and a recording medium using a liquid crystal material, a liquid crystal material is sandwiched between two transparent substrates each having a transparent electrode layer and a change in liquid crystal orientation due to an electrical action is utilized. There is a method of storing and erasing information by utilizing the phase change and orientation change of liquid crystal caused by the action of light. The former is mainly used for display and the latter is mainly used for optical recording. .

The former liquid crystal optical element by electric action uses (1) changes in birefringence, optical rotatory power, and light scattering due to the strength of an electric field in the nematic phase (N phase) of liquid crystal for display. , (2) Chiral smectic C phase (S
In the (c ^* phase), bistability of liquid crystal orientation change and change in birefringence due to electric field strength are used for display,
(3) Phase transition in cholesteric phase (Ch phase)-
It is known that light scattering or phase transition-birefringence change is controlled by the strength of an electric field for display. Further, there is a guest-host type in which a dye is added as a guest to these liquid crystal phases to display information by utilizing the dichroic change accompanying the liquid crystal alignment change by the electric field.

[0004] On the other hand, examples of the information that can be stored and erased by utilizing the phase change or orientation change of the liquid crystal caused by the action of light include, for example, a photochromic compound such as azobenzene in a low molecular weight or high molecular weight nematic liquid crystal. That utilizes the phase change of the liquid crystal induced by the photochromism (“OPTONES (OPTONE
WS) ”, No. 3, 1993, p. 16), which uses a photochromic compound-induced liquid crystal alignment change as a nematic liquid crystal element by bonding a photochromic compound to the substrate surface (Kawanishi, Ichimura, Japan). Journal of the Photographic Society, 52nd
Vol. 413 (1989)) and the like are known.

Further, two sheets having a polarizing plate, a transparent electrode layer and an alignment film described in JP-A-5-51584 and "NATURE" (No. 361, issued on February 4, 1993). By applying an electric field to the liquid crystal optical element in which the ferroelectric liquid crystal containing the photochromic compound is interposed between the transparent substrates, the polarization of the liquid crystal molecules is aligned in the same direction, and then the reverse electric field below the coercive field is applied. There is a method in which the photochromic compound contained in the photochromic compound is photo-isomerized to induce a change in the alignment of liquid crystal molecules by applying light while applying, and the change in the alignment of the liquid crystal is used to write and record information by light.

[0006]

Since the conventional liquid crystal optical element can change the orientation only between the electrodes, the display capacity and the resolution are limited by the size and shape of the electrodes. On the other hand, in the recording method by optical writing, since the orientation is not changed by the electric field, the display capacity and the resolution are not restricted by the shape of the electrodes and the like. On the other hand, a photochromic compound such as azobenzene is dissolved in a low molecular weight or high molecular weight nematic liquid crystal, and a method of recording information by utilizing the phase change of the liquid crystal induced by the photochromism, or a photochromic compound on the substrate surface The method of recording by inducing a change in liquid crystal orientation by photochromism of the substrate surface by utilizing the photochromic compound-induced change in liquid crystal orientation uses a photochromic compound as a guest and is irradiated. The photochromic compound dissolved by light or the photochromic compound bound to the substrate surface undergoes photoisomerization, and the morphological change of this guest molecule propagates to induce the phase structure of the entire system. Then, the transmission / blocking of light is performed.

However, this method requires a time for inducing a change in the phase structure in the entire system and has a slow response time of several tens of milliseconds to several hundreds of milliseconds, which is not suitable for high-speed information processing. It had drawbacks. Therefore, the inventors of the present invention, in Japanese Patent Application No. 6-150941, use a liquid crystal composition containing a photochromic liquid crystal compound exhibiting liquid crystallinity in which liquid crystal molecules themselves are provided with liquid crystal responsiveness. We have proposed a method to induce high-speed information processing by inducing a structural change in the entire system at the same time, and in this method, in particular, when the operating temperature is high, the phase structural change induced by photoisomerization is induced. After that, it reversibly returned to its original state in a few tens of seconds, and it was not suitable for maintaining the phase structure change due to photoisomerization for a long period of time.

The problem to be solved by the present invention is to obtain a high-speed response of several hundred microseconds or less, which is not possible even in a polymer liquid crystal, and to perform a switching operation of the reading light by the writing light. It is an object of the present invention to provide an optical switching method capable of storing data for a long time, erasing information at high temperature, and capable of repeatedly writing and erasing.

[0009]

In order to solve the above problems, the inventors of the present invention have conducted extensive studies on a liquid crystal optical element utilizing the phase change of liquid crystal by light, and as a result, have found that the liquid crystal molecules themselves have photoresponsiveness. By using a polymer liquid crystal compound having an added mesogenic group exhibiting photochromism as a side chain, the mesogenic group of each side chain is simultaneously induced to undergo a three-dimensional structure change by irradiation with light 1 (writing light), and the phase of the entire system is induced. By changing the structure, the orientation of the mesogenic group with a fast response is changed and the retardation (retar
The present invention has been completed by finding a photoresponsive liquid crystal optical element capable of changing the transmitted light amount of the light 2 by changing the dation) at a high speed.

That is, in order to solve the above-mentioned problems, the present invention (1) applies light to a layer made of a polymer liquid crystal compound having a mesogenic group having photochromism as a side chain, which is provided on an alignment-treated substrate. A photoswitching method utilizing a change in retardation induced by photoisomerization caused by irradiation, and (2) a polymer liquid crystal having photochromism-provided mesogenic groups as side chains provided on an alignment-treated substrate. Provided is an optical switching method utilizing a change in retardation induced by photoisomerization caused by irradiating a layer composed of a liquid crystal composition containing a compound with light.

In general, side chain type polymer liquid crystals are known to have extremely poor electric field response because one end of a mesogen group as a side chain is fixed to the main chain and the mobility of the mesogen group is reduced. There is. However, when a few percent of a photochromic compound as a guest molecule is added to a polymer liquid crystal exhibiting liquid crystallinity, the liquid crystal phase is converted to an isotropic phase from 50 milliseconds to several minutes due to photoisomerization of the photochromic compound by irradiation with light. The response of 100 milliseconds changes faster than the response to the electric field. or,
When a few% of the photochromic compound is added as a guest molecule to the low-molecular liquid crystal composition, the liquid crystal phase undergoes a phase transition to an isotropic phase at a similar rate when irradiated with light. This means that the liquid crystal phase transition due to photoisomerization is not significantly affected by the mobility of the mesogen group even if the mesogen group is fixed on the main chain of the polymer and the mobility is significantly reduced. Since a photochromic structure is introduced into the mesogenic group of the side-chain type polymer liquid crystal, Japanese Patent Application No. 6-150941 can be used.
The liquid crystal phase transition rate of several hundred microseconds can be obtained, which is similar to the case where the photochromic structure is introduced into the low-molecular liquid crystal compound described in No.

On the other hand, when comparing the retention characteristics of the isotropic phase after the phase transition from the liquid crystal phase to the isotropic phase, the retention characteristics after the isotropic phase transition from the liquid crystal phase due to photoisomerization are thermally changed in the low-molecular liquid crystal. On the other hand, it may be unstable and may reversibly transition to the original liquid crystal phase in a few tens of seconds to a few minutes, which may be unsuitable for applications such as an optical writing recording medium. In the side chain type polymer liquid crystal, when the glass transition point Tg is higher than room temperature, at the temperature of Tg or higher, the information is written into the liquid crystal phase with light 1 and the phase transitions to the isotropic phase. By setting the Tg to Tg or less, the mesogen group is frozen, and the written information can be stored for a long time. Further, even when Tg is lower than room temperature, the mesogenic group oriented in a certain direction by the orientation treatment or the like writes information by light 1, so that the mesogenic group can undergo a phase transition to an isotropic phase by photoisomerization. ,
Photoisomerization of mesogenic groups is thermally unstable, and even when reversible from trans to cis reversibly, one side of the mesogenic groups is fixed to the polymer main chain because of the side chain type polymer liquid crystal, which limits mobility. Therefore, the orientation state before the irradiation of the light 1 (writing light) cannot be restored, and the orientation state of the written portion is random, and the information is stored for a long time because it is different from the already oriented state. be able to. In any case, when erasing information and writing again, heating to a high temperature enhances the mobility of the mesogen group, and by orienting the mesogen group in a certain direction by an alignment film or alignment treatment, the mesogen group is aligned. Information can be erased and can be reused as a recording medium.

The polymer liquid crystal exhibiting photochromism used in the present invention is a polymer liquid crystal compound having a side chain of a mesogenic group exhibiting photochromism in which a photoresponsive property is imparted to a part of the molecular structure. It suffices that a part of the molecular structure of is reversibly changed to cis-trans form by the action of light. The molecular structure of the mesogen group is such that two ring structure groups are bonded to each other through a central bonding group in the core part of the molecule, an end group is bonded to one of both ends thereof, and the other is connected to the main chain of the polymer liquid crystal. A spacer such as a methylene group is bonded between them.

Examples of the two ring structures include paraphenylene, condensed ring, heterocyclic ring, non-six-membered ring, saturated ring and heterocyclic ring. These ring structures include halogen, methylene group and cyano group. It may have a substituent such as

The central bonding group is, for example, a triple bond,
A double bond, a single bond, an ester bond, etc. are mentioned. Examples of the terminal group include an electron donating group such as an alkyl group, an electron withdrawing group such as a halogen or a cyano group, an asymmetric carbon, and a branched carbon chain.

The photochromic structure has, for example, a structure such as azobenzene, stilbene, indigo or thioindigo which induces a photogeometric isomerization reaction, and further includes spiropyran, spirooxazine, fluked and the like which cause a ring opening reaction by photoelectrons. It may have a structure. Then, the molecular structure exhibiting these photochromisms is bonded to one of the terminal groups of the molecular structure in the mesogenic group or the central bonding group, and the molecular structure exhibiting the photochromism of these terminal groups and the central group is cis or In the trans form, liquid crystallinity can be obtained by the rod-shaped three-dimensional structure of the entire molecule. Further, as the spacer on the other end of the molecular structure of the mesogen group, for example, an alkylene group [-(-
CH ₂ -) _n -] or alkylene group [- (- CH ₂
-) _N- O-] or the like is introduced, and the length of the carbon number of the spacer is adjusted to obtain a desired type of liquid crystal phase, phase sequence of liquid crystal phase, and temperature range. In the polymer liquid crystal precursor, the alkylene group [-(-CH ₂
-) _n -] or alkylene group _{[- (- CH 2 -)} n
-O-] is linked to the functional group via a bonding group. Examples of the bonding group include an ether group, a urethane group, an ester group, and the like.

Further, the polymer liquid crystal compound having a mesogenic group having photochromism as a side chain used in the present invention is, for example, (1) a precursor of a side chain type polymer having mesogenic groups having different structures is mixed. And (2) a polymer liquid crystal compound obtained by cross-linking only a precursor of a side chain polymer liquid crystal having the same structure, (3)
Examples thereof include a polymer liquid crystal compound obtained by mixing and cross-linking with a polymer precursor having no mesogen group. Further, a composition composed of a polymer liquid crystal compound may be used. For example, a composition of a polymer liquid crystal compound having a mesogen group exhibiting different types of photochromism, a composition comprising a polymer liquid crystal compound having a mesogen group exhibiting a photochromism including a low molecular weight liquid crystal composition, and the like can be mentioned.
The above method can be selected for the purpose of using the liquid crystal optical element, the desired liquid crystal phase, the desired glass transition point Tg, the phase sequence of the liquid crystal phase, the temperature range of the desired liquid crystal phase, and the like. For example, (1) a method of adjusting the Tg of the resulting composition by adding a polymer precursor having a low Tg to a side chain type polymer liquid crystal exhibiting photochromism, and (2) including a low molecular weight liquid crystal composition A side chain type polymer liquid crystal composition exhibiting photochromism, and (3) a side chain type polymer liquid crystal compound having a mesogen group exhibiting photochromism and a polymer liquid crystal compound having a mesogen group not exhibiting photochromism as a side chain. When the content of the polymer liquid crystal compound having a mesogenic group exhibiting photochromism in the composition is reduced to widen the temperature range of a desired liquid crystal phase, the composition of Example 1 has sensitivity to light 1 and light 2
There is a tendency for the response speed of switching to become slower, and when the temperature range is emphasized for use, or when the response speed is emphasized, the addition amount can be adjusted to satisfy the purpose of use.

The side chain type polymer liquid crystal having a mesogenic group exhibiting photochromism as a side chain contained in the composition is preferably in the range of 50 to 100% by weight in the composition.

The desired liquid crystal phase used in the present invention is preferably a nematic phase, a cholesteric phase, a smectic phase or the like. In order to perform the optical switching operation in the smectic phase, it is preferable to use a material in which the phase sequence of the liquid crystal phase is an isotropic phase → nematic phase or a cholesteric phase → smectic phase from the high temperature side.

Among polymer liquid crystal compounds having a mesogenic group having a photochromic molecular structure as a side chain, examples of a mesogenic group exhibiting a nematic phase are listed below. A mesogenic group having an asymmetric carbon at the terminal group of liquid crystal molecules exhibits a cholesteric phase.

[0021]

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[0022]

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Among the polymer liquid crystal compounds having a mesogenic group having a photochromic molecular structure as a side chain, examples of mesogenic groups exhibiting a smectic phase are listed below.

[0024]

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The desired temperature range of the liquid crystal phase and the desired liquid crystal phase are preferably obtained at least near room temperature.

The liquid crystal optical element used in the optical switching method of the present invention is composed of a polymer liquid crystal compound having a mesogenic group exhibiting photochromism as a side chain or a composition containing these polymer liquid crystal compounds. A thin film of the polymer liquid crystal layer may be formed by orienting the mesogen group exhibiting photochromism and the mesogen group in the composition by using an aligning means. When the precursor of the polymer liquid crystal compound exhibits liquid crystallinity, After forming a thin film of the precursor, the thin film of the polymer liquid crystal layer can be formed by polymerizing.
When the precursor does not show liquid crystallinity, the precursor is subjected to addition reaction or addition polymerization to obtain the polymer liquid crystal compound or composition, and then the polymer liquid crystal compound or composition is dissolved in a solvent. It is also possible to prepare a solution, apply the solution in the form of a thin film to orient the mesogenic groups, and dry the solution to form a thin film.

Means for forming a thin film of a liquid crystal phase on the substrate include, for example, (1) for adjusting the thickness of a liquid crystal layer between two substrates having an alignment film when the precursor exhibits liquid crystallinity. After interposing a spacer, by sealing other than the injection port, a method of filling the precursor of the photochromic polymer liquid crystal compound into a desired gap distance by a vacuum injection method or the like,
(2) A method of dropping the precursor of the compound on one substrate, or a method of forming a thin film having a desired film thickness on one substrate by spin coating, bar coating, roll coating, or the like.
(3) A method of forming on one substrate by a dipping method can be mentioned. When the precursor does not exhibit liquid crystallinity, a thin film is formed by the methods (2) and (3) of the above thin film forming methods, and then the precursor is added to the polymer liquid crystal by an addition reaction or an addition polymerization method. The method of forming a phase thin film is mentioned.

Examples of the orientation means include (1) a polymer orientation film coated on a smooth glass substrate with monomers and / or oligomers such as polyvinyl alcohol and polyimide, and cured, and then rubbed. And then
An alignment film is formed. At that time, it is sufficient that at least one of the substrates has an alignment film subjected to an alignment treatment and uniaxial alignment is obtained. Further, as other alignment films, (2) oblique vapor deposition film of SiO, (3) polymer LB film, etc. can be used.

It is preferable that the polymer liquid crystal compound having a mesogenic group exhibiting photochromism as a side chain has a thin film of a liquid crystal phase having a thickness of 300 nm or less formed on the substrate having these alignment means.

After forming the thin film, another substrate can be placed on the thin film as a protective cover. The newly arranged substrate may be a hard substrate such as glass or a soft substrate such as a polymer film, or may have an alignment film.
The substrate and the entire polymer liquid crystal phase thin film may be laminated with a polymer film.

The optical switching method of the present invention is characterized by a liquid crystal phase transition in which a mesogenic group exhibiting photochromism as a side chain in a side-chain type polymer liquid crystal compound is caused by reversible cis-trans photoisomerization. It is possible to control the blocking of light transmission by utilizing the change in retardation due to, and since the liquid crystal molecular structure and the photochromic molecular structure are bonded to the side chain of the polymer liquid crystal compound, the photoisomerization of each molecule At the same time, a liquid crystal phase transition is induced, and the entire system changes at once to obtain high-speed response.

For example, as shown in FIG. 1, when the side chain of the polymer liquid crystal has a mesogen group having a photochromic structure and shows a liquid crystal phase in the trans form, the polymer liquid crystal compound aligned on the substrate is Irradiation with light 1 causes photoisomerization in the cis isomer to cause a phase transition from the liquid crystal phase to the isotropic phase. As shown in FIG. 3, the optical properties are different between the liquid crystal phase and the isotropic phase, and the retardation changes. Therefore, by utilizing this optical change, the optical characteristics are changed by using a polarizer and a phase plate. 2 can be transmitted or blocked.

In order to transmit or block the light 2 depending on the change in retardation, when two polarizers are orthogonal to each other, they are arranged on both sides of a substrate having a thin film liquid crystal phase,
It is arranged so that the orientation direction of the mesogenic group showing the photochromism of the side chain of the polymer liquid crystal exhibiting liquid crystallinity with respect to the polarization direction of one of the polarizers is 45 degrees. When the mesogenic group is in the liquid crystal phase, the light 2 is transmitted, and when the liquid crystal phase changes to the isotropic phase due to the phase transition induced by the light 1, the light 2 is blocked. When the mesogenic group is a cholesteric liquid crystal phase, a Granger or planar orientation is obtained, the polarization direction of the incident linearly polarized light is rotated by the optical rotatory power, and when the rotated light and the polarizing plate on the exit side are orthogonal, 2 can be cut off. When this state is irradiated with light 1, the compound changes to an isotropic phase due to a photophase transition associated with photoisomerization, resulting in loss of optical activity.
Since the incident linearly polarized light passes through the other polarizer, the light 2 changes from the light blocking state to the light transmitting state and operates as an optical switch.

Further, since the retardation is represented by the product of the optical anisotropy Δn of mesogen and the thickness d of the polymer liquid crystal phase of the thin film, the retardation can be changed by adjusting d, When the light 2 is white light, the hue of the birefringent color of the transmitted light of the light 2 is changed as necessary,
It is also possible to perform optical switching by transmitting the light 2 due to the birefringent color and blocking the light 2 due to the isotropic phase. When the light 2 is monochromatic light, the intensity I _{o of} light incident on the element, the wavelength λ of monochromatic light,
When the retardation is R, the transmitted light intensity I of light 2 is

[0035]

## EQU1 ## I = I _o sin ² (πR / λ)

Since it depends on the retardation R, it is preferable to adjust the retardation Δn · d according to the wavelength λ of the light 2 used to maximize the transmitted light intensity I. .

In the optical switching method of the present invention for switching the light 2 with the light 1, it is preferable to design the optical system according to the purpose of use so that the output side of the optical path of the light 2 is not affected by the light 1. For example, the intersection of the optical axis of the light 1 and the optical axis of the light 2 is provided in the polymer liquid crystal thin film on the substrate, and the optical axis of the light 2 is aligned with the normal direction of the substrate. It is preferable that the optical axis of the light 1 does not coincide with the optical axis of the light 2 and the incident angle of the light 1 is set in a range larger than the normal direction of the substrate and smaller than the critical angle θc. (Between the optical axis critical angle θc of light 1 and the refractive index ns of the substrate and the refractive index n _{0 of} air,

[0038]

[Equation 2] sin θc = n ₀ / ns

There is a relationship of In this case, there is no polarizer on the optical axis of the light 1, and the polarizers arranged on both sides or one side of the substrate are arranged on the optical axis of the light 2.

When the light 1 and the light 2 are single-wavelength lights and the wavelengths are preferably different by 100 nm or more, the light 1 and the light 2 are incident on the liquid crystal substrate coaxially or close to each other, and an optical filter such as an interference filter is used. It is also possible to use a polarizer, a polarization beam splitter, a phase plate or the like to cut the light 1 and allow the liquid crystal optical element to output only the light 2. Light 1 and light 2 are a right-angle prism, a penta prism, a 45-degree deviation prism, a 30-degree deviation prism, a single lens, a compound lens, a cylindrical lens, an aspherical lens, an optical fiber, a reflecting mirror, a semi-transparent mirror, and a polarization beam splitter prism. , A polarization beam splitter plate, a phase plate, etc. can be used to deviate, combine, demultiplex, and condense the light and make it incident on the liquid crystal optical element at a desired incident angle.

The light source used in the optical switch of the present invention is
In the light 1, a laser and an electric lamp that oscillate at a wavelength that causes photoisomerization of the photochromic compound having liquid crystallinity used in the present invention can be used. As such a laser and an electric lamp, for example, He- Ne laser, C
O ₂ laser, Ar laser, Kr laser, He-Cd laser,
Nitrogen laser, excimer laser, ruby laser, YAG laser, glass laser, dye laser, semiconductor laser, metal halide lamp, fusion lamp, mercury lamp, xenon lamp and the like can be mentioned. Further, the wavelengths of various lasers can also be used after being converted into the second harmonic by a non-linear crystal.

The polarizer used in the present invention is a glass prism or an alternating multi-layered film of dielectric materials having different refractive indexes on the surface of a parallel substrate, and vacuum vapor deposition or the like so that the Brewster condition is satisfied at the interface of each film. It is obtained by applying a polarizing film with
Polarizers such as polarized beam splitter prisms and polarized beam splitter plates that utilize reflected or transmitted light,
Glan-Thompson prism as a single-image prism that utilizes the birefringence of crystals, a double-image prism, and polarizers such as Senarmont, lotion, and Wollaston prism, and calcite and rutile that have a large difference in refractive index between ordinary and extraordinary rays. A birefringent plate of a parallel plane plate used as a substrate material, a polymer film in which a halogen substance such as iodine or a dye as a dichroic substance is adsorbed or dispersed in a micelle space of a polymer transparent film in which micelles are arranged in a certain direction. And the like.

[0043]

EXAMPLES The present invention will be described in more detail below with reference to examples. However, the invention is not limited to these examples.

(Example 1) Expression

[0045]

[Chemical 4]

An acrylic monomer having an azobenzene skeleton (A as a photoresponsive side chain type polymer liquid crystal represented by
6AB2) 2 mmol in benzene 10 ml was added with azobisisobutyronitrile 0.2 mmol, vacuum degassing was performed 3 times, and the reaction vessel was sealed.
It was left at 60 ° C. for 48 hours. After the completion of the polymerization, the polymer was precipitated in a methanol solvent, and the polymer obtained by filtration was dissolved in methyl chloride, and then dissolved in dichloromethane 50 again.
It was reprecipitated with 0 ml, filtered off and dried. The obtained polymer is dissolved in chloroform, a solution containing the polymer is dropped onto a glass substrate which is coated with polyvinyl alcohol as an alignment film and rubbed, and then dried to form a liquid crystal device having a 100 nm thin film of polymer liquid crystal. It was made.

Polymer obtained by polymerization (PA6AB2)
Is a side chain type polymer liquid crystal compound having a mesogen group exhibiting photochromism, and the mesogen group having an azobenzene skeleton has a Tg of 45 ° C. in the trans form,
A phase transition from a nematic phase to an isotropic phase occurred at 155 ° C.

When the obtained liquid crystal element was observed with a crossed Nicols polarization microscope, a texture of a nematic liquid crystal phase was observed. Also, when the amount of transmitted light was monitored while rotating with respect to a polarizing microscope, bright and dark appeared at every 45 °, and it was confirmed that uniaxial orientation was achieved. The third harmonic (wavelength 355 nm) of the YAG laser was used as the writing light 1, and the semiconductor laser (830 nm) was used as the reading light 2. Light 1
The intersection of the optical axis of light 2 and the optical axis of light 2 is provided in the liquid crystal thin film on the substrate, and the optical axis of light 2 is aligned with the normal direction of the liquid crystal element.
Two polarizers of crossed Nicols were arranged on the optical axis of 1 so as to be sandwiched by a distance of 5 cm from the produced liquid crystal element. Further, one side of the liquid crystal element is the input side of the switch, the semiconductor laser of the light source is arranged on the optical axis of the light 2 on the element input side, and the other side is the output side of the switch, and the photomultiplier tube is on the optical axis of the light 2. Was installed so that a change in transmitted light of light 2 could be observed with a synchroscope. The angle formed by the uniaxial alignment direction of the liquid crystal element and the polarization direction of the polarizer was 45 °.

The optical axis of the light 1 is 20 with respect to the normal line of the liquid crystal element.
It is installed at an angle of ゜, the temperature is 140 ℃, and the light intensity is 70mJ.
Irradiation was performed with 10 nanosecond pulsed light having a wavelength of 355 nm / cm ² and a wavelength of 355 nm. By the irradiation of light 1, the amount of transmitted light 2 changed from the transmitted state to the blocked state with a high-speed response of 200 μs, which was not possible in the past. When the liquid crystal element of the present invention after irradiation with light 1 was observed with a polarization microscope, the portion irradiated with light 1 was changed to an isotropic phase, and it was observed that the nematic liquid crystal phase had undergone an optical phase transition. When light 1 having a wavelength of 355 nm was irradiated and light 1 having a wavelength of 450 nm was irradiated on the same optical axis, the amount of transmitted light 2 changed from a blocked state to a transmitted state with a high-speed response of 17 milliseconds. When a portion irradiated with the light 1 was similarly observed with a polarization microscope, a uniaxially aligned nematic liquid crystal phase was observed.

As described above, the liquid crystal element of the optical switch of the present invention can be repeatedly operated as an optical switch by causing reversible photoisomerization by changing the wavelength of the light 1.

Further, the temperature of 140 ° C.
After inducing photo-isomerization with a nematic phase to an isotropic phase transition and changing from bright to dark for 200 μsec, 140 ° C
When left in a dark place, the phase transition from the isotropic phase to the nematic phase took place in about 7 seconds and the operation could be repeated.

(Example 2) In the same manner as in Example 1, a liquid crystal device having a 100 nm thin film of polymer liquid crystal on a glass substrate was prepared.

A liquid crystal element having the same structure as in Example 1 was arranged between two polarizers, and the light intensity was 70 mJ at room temperature.
Light 1 having a wavelength of 355 nm / cm ^{2 was} irradiated through a photomask to induce a photophase transition and an image was recorded. A change in the transmitted light amount of the light 2 having a wavelength of 633 nm during recording was observed with a synchroscope. A high-speed response of 200 μs from the transmission state to the blocking state was also observed in the polymer liquid crystal. Further, the recorded element was stored at 25 ° C. or lower for 1 year or more, but no change was observed in the recorded image. After storing for one year, the device was heated to 140 ° C. in order to erase the image. In about 7 seconds, the isotropic phase phase transitioned to the liquid crystal phase and the image disappeared. As described above, it was confirmed that the recorded image can be stored for a long period of time, the image can be erased by heating, and the recording medium functions as a repeatable optical writing medium.

(Embodiment 3) Expression

[0055]

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A side chain type polymer liquid crystal compound (PA6AB2) represented by azobenzene having a mesogen group was polymerized in the same manner as in Example 1, and the obtained side chain type polymer liquid crystal compound was dissolved in chloroform solvent. Dissolved. 4-butyl-4'-methoxyazobenzene (BMA
10% by weight of B) was added to the side chain type polymer liquid crystal compound. A substrate having an alignment-treated PVA alignment film is dipped in this solution and then dried to give a thickness of 150 on the substrate.
A liquid crystal element having a thin film of nm was prepared.

A liquid crystal element having the same structure as in Example 1 was arranged between two polarizers, and a photomask of light 1 having a light intensity of 70 mJ / cm ² of a YAG laser third harmonic and a wavelength of 355 nm was placed at room temperature. An image was recorded by irradiating the mesogenic group with a light to induce a photophase transition from the nematic phase to the isotropic phase accompanying the photoisomerization of the mesogen group from the trans form to the cis form. When recording,
As a result of observing the change of the transmitted light amount of the read light 2 of wavelength 633 nm with the synchroscope, it is possible to change from the transmitted state to the blocked state.
A high-speed response of 15 μsec was also observed in the polymer liquid crystal composition. Further, the recorded element was stored at 25 ° C. or lower for one year or more, but no change was confirmed in the recorded image. After storing for one year, the element was heated to 140 ° C. to erase the image, and in about 7 seconds, the isotropic phase portion changed to a liquid crystal phase and the image disappeared.

As described above, it was confirmed that the recorded image can be stored for a long period of time, the image can be erased by heating, and the recording medium functions as a repeatable optical writing medium.

[0059]

According to the optical switching method of the present invention,
A side chain type polymer liquid crystal having a mesogenic group exhibiting photochromism is used.
A high-speed response of less than a second can be obtained, and the reading light can be switched by the writing light. Further, the information written by optical writing can be stored for a long period of time, information can be erased at high temperature, and repeated writing and erasing are possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a state of photoisomerization caused by irradiating light to a polymer liquid crystal compound molecule having a mesogenic group showing a photochromism side chain in a liquid crystal optical element in the optical switching method of the present invention. Is.

FIG. 2 is a layout view of a liquid crystal optical element, a light source, an optical axis and a polarizer in the optical switching method of the present invention.

FIG. 3 is a diagram illustrating a case where two polarizers are orthogonal to each other in the optical switching method according to the present invention, depending on whether or not the light 2 acts.
FIG. 6 is a schematic diagram showing how light is transmitted and blocked.

Claims (12)

[Claims] 1. A retardation induced by photoisomerization caused by irradiating light on a layer made of a polymer liquid crystal compound having a mesogenic group exhibiting photochromism as a side chain, which is provided on an oriented substrate. optical switching method characterized by utilizing a change in retardation). 2. An alignment-treated substrate and a layer made of the polymer liquid crystal compound provided on the substrate are sandwiched between two polarizers whose polarization directions are orthogonal to each other. The optical switching method according to claim 1. 3. The alignment direction of the mesogenic groups of the alignment-treated substrate and the layer formed of the polymer liquid crystal compound provided on the substrate is homogeneously aligned. Optical switching method. 4. The orientation direction of the orientation-treated substrate and the layer made of the polymer liquid crystal compound provided on the substrate is 45 degrees with respect to one polarization direction of two polarizers whose polarization directions are orthogonal to each other. The optical switching method according to claim 1, wherein the optical switching method is inclined. 5. Triggered by photoisomerization caused by irradiating light to a layer made of a liquid crystal composition containing a polymer liquid crystal compound having a mesogenic group having photochromism as a side chain, which is provided on an alignment-treated substrate. Retardation (retardat
ion) change is utilized. 6. A layer made of an alignment-treated substrate and a liquid crystal composition containing the polymer liquid crystal compound provided on the substrate is sandwiched between two polarizers whose polarization directions are orthogonal to each other. The optical switching method according to claim 5, wherein: 7. The alignment direction of the mesogenic groups of the alignment-treated substrate and the layer made of the liquid crystal composition containing the polymer liquid crystal compound provided on the substrate is homogeneously aligned. 5. The optical switching method according to 5 or 6. 8. A polarization direction of one of the two polarizers in which the alignment direction of the alignment-treated substrate and the layer formed of the liquid crystal composition containing the polymer liquid crystal compound provided on the substrate are orthogonal to the polarization direction. 9. The optical switching method according to claim 5, wherein the optical switching method is inclined at 45 degrees with respect to. 9. The optical switching method according to claim 1, wherein the polymer liquid crystal compound having a mesogenic group exhibiting photochromism as a side chain is an azobenzene derivative. 10. The optical switching method according to claim 1, wherein the polymer liquid crystal compound having a mesogenic group exhibiting photochromism as a side chain is a spirolylan derivative. 11. The polymer liquid crystal having a mesogenic group exhibiting photochromism as a side chain is a polyacrylic acid ester having a mesogenic group exhibiting photochromism in a side chain or a polymethacrylic acid ester. 3, 4, 5,
The optical switching method according to 6, 7, 8, 9 or 10. 12. The polymer liquid crystal having a mesogenic group exhibiting photochromism as a side chain is polystyrene or polysiloxane having a mesogenic group exhibiting photochromism in a side chain, or a polysiloxane. , 6, 7, 8, 9 or 10
The optical switching method described.