JPH0444331B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is composed of a liquid crystal cell made by dissolving and dispersing an azobenzene-based photochromic compound in a twisted nematic liquid crystal, which prevents recording loss due to readout and achieves high sensitivity. The present invention relates to an optical memory device from which records can be read.

BACKGROUND OF THE INVENTION Photochromic compounds are useful as constituents of reversible optical memory materials for the purpose of writing and erasing information. However, since there is no threshold for photoreaction, the written information gradually disappears due to repeated irradiation with readout light. As a means to overcome this drawback, efforts have been made to utilize the property that optical rotation can be detected even in a wavelength range far from the absorption band, and to convert and detect changes in the chemical structure of photochromism into changes in optical rotation. For example, an optical memory material using a polymeric cholesteric liquid crystal as a medium for dispersing a photochromic compound has been proposed (Japanese Patent Laid-Open No. 62-209186). this is,
The principle is that when the photochromic molecules are dissolved and dispersed in the helical structure of the cholesteric liquid crystal, optical rotation is induced in the photochromic molecules by the helical structure. Therefore, the change in optical rotation is detected by adding the change in optical rotation caused by photochromism to the large optical rotation of the cholesteric liquid crystal phase, but the optical rotation based on this helical structure is the same as the optical rotation caused by photochromism. Since it is extremely sensitive to changes, it was necessary to set the pitch length with high precision. However, since the pitch length is often affected by the liquid crystal cell configuration conditions, liquid crystal development conditions, temperature, etc., optical memory materials using such cholesteric liquid crystal matrices may have variations in optical rotation between samples. However, there were problems in detecting the optical rotation accurately and with high sensitivity.

Problems to be Solved by the Invention The present invention improves the drawbacks of conventional reversible optical recording using photochromism, and provides a novel optical memory element that does not cause record destruction due to readout light and can detect recorded information with high sensitivity. It provides:

Means for Solving the Problems The present inventors have conducted extensive research in order to develop an optical memory material that can prevent records from being erased by readout light and that can read records with high sensitivity. The liquid crystal phase corresponds to the spiral groove partial structure of the cholesteric liquid crystal phase, and furthermore,
The spiral structure can be arbitrarily set by setting the angle of the orientation processing direction of two substrates subjected to parallel orientation processing (for example, if two substrates are used with the orientation processing directions perpendicular to each other) Focusing on the fact that the liquid crystal phase has a quarter helical structure and an optical rotation of 90 degrees, we used twisted-state nematic liquid crystal instead of cholesteric liquid crystal, and used azobenzene-based photochromic as the photochromic compound. The inventors have discovered that by using a compound based on the optical rotation, the optical rotation is constant, and variations in liquid crystal cells can be resolved, and the amount of change in the optical rotation due to photochromism is large.Based on this knowledge, the present invention was accomplished.

That is, the present invention involves dissolving a photochromic compound in a twisted nematic liquid crystal in which a nematic liquid crystal phase is twisted between two transparent substrates constituting a liquid crystal cell, and producing a reversible photochromic solution of an azobenzene-based photochromic compound. The object of the present invention is to provide an optical memory element capable of converting a structural change accompanying a reaction into a change in optical rotation of a twisted nematic liquid crystal cell and reading the result.

For the liquid crystal cell substrate used in the present invention, transparent silica glass, hard glass, quartz glass, and various transparent polymer sheets are used. In the present invention, it is necessary to orient the above-mentioned substrate in advance using a known method (see Shoichi Matsumoto and Ichiyoshi Tsunoda, "Latest Technology of Liquid Crystals - Physical Properties, Materials, Applications", Industrial Research Association, 1984). . That is, these substrates are treated with an oblique vapor deposition method, or a thin film of polyvinyl alcohol or polyimide is applied and rubbed lightly with a cotton cloth.

In the present invention, a liquid crystal compound in which a photochromic compound is dissolved is placed on this alignment-treated substrate, and then another alignment-treated substrate is placed on top of this. At this time, it is necessary to configure the liquid crystal cell so that the alignment directions of the two alignment substrates are at a certain angle, for example, 90 degrees. In order to adjust the thickness of the liquid crystal cell, spacers such as polymer fine particles or glass rods can be used. Alternatively, it is also possible to fill an empty cell container sealed with a thermosetting resin, photocurable epoxy resin, etc. with liquid crystal, as in the production of display liquid crystal cells. (See the above-mentioned literature).

The azobenzene-based photochromic compound used in the present invention is a photochromic compound having azobenzene as its basic skeleton, such as 4-methoxyazobenzene and 4-(2-methylbutoxy)-4'-pentylazobenzene.

In addition, the liquid crystal can be arbitrarily selected from conventionally known nematic liquid crystal materials (A. Be'guin et al, Molecular Crystals and
(See Liquid Crystals, Vol. 115, No. 1-4 (1984)). Also, even if it is a smectic type,
A material that assumes a nematic liquid crystal phase at a certain temperature can be used. It goes without saying that liquid crystal substances include not only low-molecular substances but also high-molecular substances.

In the present invention, it is necessary to use these liquid crystal materials in a twisted nematic state by twisting the liquid crystal molecules by aligning the alignment direction of the alignment substrate at a certain angle, for example, perpendicularly. In particular, when the alignment treatment directions are orthogonal, an optically active substance may be added to the liquid crystal compound in order to set the twist direction clockwise or counterclockwise, or the azobenzene-based photochromic compound itself may be an optically active substance. It's okay to be.

The amount of the azobenzene photochromic compound added is in the range of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the weight of the liquid crystal.

The thickness of the liquid crystal cell can be arbitrarily selected from 2 to 50 microns. Furthermore, by stacking a birefringent plate on the liquid crystal cell prepared in this manner, it is possible to further increase the amount of change in the optical rotation.

Effects of the Invention In the optical memory material of the present invention, information is read by measuring the change in optical rotation caused by optical writing, that is, the change in the rotation angle of linearly polarized light. The wavelength of the linearly polarized light may be beyond the wavelength range used in photochromism, so it is possible to prevent the loss of records due to optical readout, and the amount of change depends on the type of azobenzene photochromic compound, its doping amount, the cull thickness, and the photoreaction. amount,
Although it varies depending on the optical rotation measurement wavelength, it is 150 to 2000 degrees when converted to a cell with a thickness of 1 mm, which is approximately 3 to 900 times larger than a system using cholesteric liquid crystals, making it possible to detect changes in memory. can be done with high sensitivity.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 To 100 mg of mixed liquid crystal of cyclohexanecarboxylic acid phenyl ester, 1 part of 4-methoxyazobenzene was added.
Add mg and 8 micron glass spacer and mix well. This mixture was poured onto a hard glass substrate which had been subjected to a rubbing alignment treatment, and another substrate which had been subjected to an alignment treatment was placed thereon so that the rubbing directions were perpendicular to each other, to obtain a twisted nematic liquid crystal cell. I combined a 500W ultra-high pressure mercury lamp and a colored glass filter into this cell and extracted it.
It was irradiated with 365 nm ultraviolet light for 20 seconds. As the azobenzene derivative changes from trans form to cis form,
The optical rotation (589 nm) changed from -88.0 degrees to -85.0 degrees. Although 589nm light does not change the cis isomer to trans isomer, when in this state irradiation with visible light >440nm or higher, the optical rotation returned to -88 degrees. Thereafter, the optical rotation was reversibly changed between -88 degrees and 85 degrees by alternate irradiation with ultraviolet light and visible light. This amount of change is converted to per millimeter of liquid crystal cell.
The amount of change will be 150 degrees.

Example 2 (S)-4-(2-methylbutoxy)-4'- in place of 4-methoxyazobenzene in Example 1
Pentyl azobenzene was dissolved in an amount of 3% by weight based on the weight of the liquid crystal to obtain a 20 micron twisted state nematic liquid crystal cell. When this cell is alternately irradiated with ultraviolet light and visible light, the optical rotation at 589 nm is 87 degrees and 47 degrees.
It changed reversibly between degrees. This amount of change is equivalent to 2000 degrees per millimeter of liquid crystal cell.

Comparative Example A copolymer of cholesteryl-4-(methacryloyloxy)butanoate and cholesteryl-11-(methacryloyloxy)undecanoate was used instead of the mixed liquid crystal of cyclohexylcarboxylic acid phenyl ester in Example 1. A polymer cholesteric liquid crystal cell was constructed. When this cell was alternately irradiated with the ultraviolet light and visible light used in Example 1, the optical rotation at 589 nm changed from -2.495 degrees to -
It changed reversibly between 2.482 degrees. This amount of change is
When converted to 1 mm of cell, it becomes 0.163 degrees.

Claims (1)

[Claims] 1. A highly sensitive optical memory element formed by dissolving and dispersing an azobenzene-based photochromic compound in a twisted nematic liquid crystal phase.