KR20000005341A - Compositions containing chiral compounds and nematic liquid crystals, and devices using them - Google Patents

Abstract

PURPOSE: A nobel chiro-optical composition and display using the chiro-optical composition is disclosed CONSTITUTION: The devices useful for storage of information comprises mixtures of suitable chiral materials with nematic liquid crystals and in which by irradiation with light of two different wavelengths the chirality of the mixture can be reversibly switched between two stable states of different chirality, corresponding to two states of different optical properties.

Description

Compositions containing chiral compounds and nematic liquid crystals, and devices using the same

For the storage of data, materials and devices with reversible optical storage capabilities are needed. Optical storage can be applied to optical computer, storage systems of audio and video information.

There are many types of optical storage that can be written only once using an irreversible storage method (write-once-read-many-systems = WORM systems). However, because of their irreversible nature, they are not suitable for computer storage systems and have limited application to audio and video information.

More useful for many purposes is a device that can be written multiple times using reversible storage (erasable-direct-read-after-write systems = EDRAW systems). For this purpose, investigations of materials for optical data storage have been carried out in M. M. Emmelius, G. G. Pawlowsky and H. W. Performed by H. W. Vollmann (Angew. Chem. Intern. Ed. 28, 1445 (1989)). However, the pursuit of new optical storage materials and devices is quite practical, because all available optical data storage media have some drawbacks such as storage density, storage speed, reversibility, long term stability.

This kind of device has traditionally consisted of layers of liquid crystal materials contained between two glass slides. By irradiation with light of different wavelengths, devices containing azo compounds change from nematic to isotropic and vice versa (eg, D. Demus, G. G. Pelzl, F. Kuschel DD WP 134 279).

Particularly for these devices liquid crystal polymers containing azo groups have been proposed (H. Finkelmann, W. Meier and H. Scheuermann, in: Liquid Crystals. Applications and Uses, Vol. 3, pages 345-370, published by B. Bahadur, Singapore World Scientific, 1992.

The proposed azo compound has a disadvantage that the irradiation intensity and irradiation time are quite large because a large amount of the azo compound has to be converted to the corresponding isomer. Therefore, the switching time is very large.

See also cholesteric awards (S. Kobayashi and A. Mochizuki, in: Liquid Crystals.Applications and Uses, Vol. 3, pp. 291-293, B. Bahader, Singapore World Scientific). Published in 1992) or Smectic A Awards (D. Coates, in: Liquid Crystals.Applications and Uses, Vol. 1, pp. 275-303, 1990 by B. Bahader, Singapore World Scientific) A thermo-optical liquid crystal device based on heat induced texture change is proposed.

Thermo-electro-optic displays include low molecular glass forming liquid crystals (D. Demus and Z. Peltz, DD WP 242 624 A1) and polymer glass forming liquid crystals (H. Finkelman, W. Meier and H. Schueermann, in: Glass Crystal, Liquid Crystals.Applications and Uses, Vol. 3, pp. 345-370, published by Singapore World Scientific, Ltd. B. Barder, 1992, takes advantage of the combined effects of the thermal and electrical fields.

Thermo-optic devices, however, typically require quite a bit of energy to locally heat the liquid crystal material.

M. M. Zhang and G. ratio. G. B. Schuster is described in J. Schuster. Phys. Chem. 96, 3063-3067 (1992) reported on photoracemization of chiral bi (naphthyl derivatives), converting cholesteric mixtures into nematic mixtures. Since this reaction is irreversible, the change from nematic to cholesteric is impossible and the material cannot be used for repeated data storage.

Holographic techniques were investigated for reversible data storage systems. Several types of materials have been investigated for this application. There are three types of materials and inorganic metal compounds, photorefractive polymers and polymer liquid crystals have been reported. But all of them have flaws.

Photorefractive crystals such as lithium niobate (LiNbO ₃ ), barium titanate (BaTiO ₃ ) and bismuth silicon oxide (Bi ₁₂ SiO ₂₀ ) have been proposed as optical data storage materials and have been studied for 25 years. However, they are difficult to grow and expensive, and their properties are not commercially viable because their properties cannot be easily modified.

Various photorefractive polymers and polymer liquid crystals have also been proposed (K. Yoshinaga et al., Japanese Patent Application Laid-Open No. 2-280116, T. Todorov et al., Applied Optics, 23 (23), 4309). (1984), M. Eich et al., Makromol. Chem., Rapid Commun., 8, 59 and 467 (1987)). The photorefractive effect has revealed that the object can store more than 100 complete images or holograms each containing one million bits of information. They can be produced easily, so they are economically beneficial. However, they have serious drawbacks. The speed at which they react to light is significantly slower than for semiconductors. And most existing polymers require the application of an electric field to orient the nonlinear optical chromophore so that the material is electro-optically active.

New data storage systems, devices, and materials that are easy to produce, have rapid advances in low viscosity, large data storage, and reversible and stable reading and writing of information have been desired. It is an object of the present invention to overcome the above deficiencies of the prior art and to provide novel data storage systems, devices and materials having the above desired properties.

The present invention relates to a display using a novel chirooptical system and a novel chirooptical medium. Specifically, the present invention relates to liquid crystal optical storage devices and systems.

1 shows a director arrangement of liquid crystals in a hybrid cell.

2 is a diagram of a holographic arrangement using the apparatus of the present invention.

Continuous research has shown that by irradiating with two different wavelengths of light, using a mixture of nematic crystals and a suitable chiral material (chiral dopants), the chirality of the mixture is in two stable states of different chirality useful for the storage of information. It has been found that it can be reversibly converted between (corresponding to two states of different optical properties).

By using two states with different optical properties induced by different chiral pitch lengths, a large number of information can be stored in the liquid crystal mixture. The system is reversible and reading and writing data can be repeated by irradiating with light having two different wavelengths. The two states are physically and chemically stable and the optical properties of the two states never change except during conversion.

The system, in particular the device, consists of a nematic liquid crystal cell containing a chiral nematic liquid crystal between two glass or plastic plates. The storage of the information can be performed within the nematic temperature range.

Since the data storage system of the present invention uses nematic liquid crystal as the data storage material, the viscosity of the material is relatively low, facilitating quick response to light irradiation.

This advantage can be induced by a combination of nematic liquid crystals, chiral dopants, nematic liquid crystal cells and light irradiation, which is a new strategy that has never been proposed before.

It will be described in more detail below. For example, for a material showing a transition between two different chiral states induced by light irradiation, the "A" form can be converted to another "B" form by irradiation with light of "C" nm wavelength, and Inverse transformation can occur by irradiation with light of different "D" nm wavelength. The conversion between the two forms need not be complete. Both states consist of a mixture of two isomers of different chirality.

A chiral compound and a mixture of the two are dissolved in a liquid crystal material, usually a multicomponent mixture, to form a cholesteric liquid crystal medium (chiral nematic mixture).

The cholesteric medium exhibits strong optical activity, which is the rotation of the linear polarizer. This material is preferably inserted between two substrates (eg glass or plastic plates) to form a hybrid cell. As shown in FIG. 1, in a hybrid cell, two substrates are aligned in a manner such that one plate liquid crystal molecules are parallel to the substrate and another plate liquid crystal molecules are perpendicular to the substrate, with or without an inclination angle. Hybrid cells filled with cholesteric material show optical activity. Two polarizers whose polarization axes are perpendicular to each other are mounted on the outside of the two substrates.

Optical activity depends on the concentration of the chiral dopant and the cell thickness. As the concentration of dopant decreases and cell thickness increases, optical activity increases. By adjusting the polarizer in the proper direction, the device shows a dark state. After irradiation with light of "C" nm wavelength, the device shows a bright state. By irradiating light with a wavelength of "D" nm in the bright state, the device returns to the dark state.

Since both dark and light conditions are stable for a long time, the device can be used to store information. Light irradiation can be carried out in a point-wise or scanning mode using a suitable laser. An entire project can be saved by projecting one picture.

The polarizer can also be adjusted in another way by first placing the device in a bright state, irradiating with light of a "D" nm wavelength and then converting it into a dark state.

The apparatus of the present invention can also be used for holographic recording of information. In this case, it is preferable to use a laser for information recording. According to FIG. 2, the laser beam is split into two beams, one of which is adjusted by a modulator. In the liquid crystal device described in the present invention, two beams interfere with each other to produce a hologram containing information. Information can be read using laser light in the visible spectrum, preferably circularly polarized laser light. By irradiating with light of another different wavelength, information can be erased.

In principle, all kinds of light, both visible and invisible, polarized and unpolarized, can be used for irradiation for conversion.

The nematic liquid crystal used in the present invention may be provided by doping a chiral compound into a conventional achiral nematic liquid crystal substrate mixture. In the present invention, when irradiated with two kinds of light having different wavelengths and when combined with a nematic liquid crystal substrate mixture, all kinds of inducing spirally twisted structures and two stable states having two different optical properties Chiral compounds can be used. In this case, the chiral compound used for doping does not need to have the property of liquid crystal.

For example, chiral compounds suitable for such devices are sterically dense chiral olefins (BL Feringa, WF Jager, B. de Lange, J Am. Chem. Soc. 113, 5468-5470 (1991); W. F. Jarger, B. de Lange, B. L. Ferringa, Mol.Cyst.Liq.Cryst. 217, 133-138 (1992) E. W. Meijer, B. L. Ferringa, Mol.Cyst.Liq.Cyst. 235, 169-180 (1993); W. F. Zager, J. C. de Chong Jong, B. de Lange, N. P. M. Huck, A. Meetsme and B. L. Ferringa, Angew. Chem. Int. Ed. Engl., 34 ( 1995), No. 3, 348-350). These can be represented, for example, by the following formula (1-1):

[Wherein Ra, Rb, Rc = alkyl, alkoxy, hydrogen, hydroxyl, nitro, dialkylamino,

X 1, X 2 = oxygen, sulfur, methylene].

Azo compounds of the general formula (1-2), which may also exist as cis or trans isomers, can also be used in the apparatus when they are substituted with chiral groups. The cis and trans isomers are different in terms of optical activity and can convert nematic liquid crystals to cholesteric materials:

[Wherein Y, Y '= oxygen, sulfur, carbonyl, ester group, 1,2-ethylene, 1,2-ethenylene, 1,2-ethynylene, 1,4-butyl regardless of another single bond Ring systems such as ethylene, methyleneoxy, oxymethylene, difluoromethyleneoxy, substituted or unsubstituted benzene, cyclohexane, heterocyclic ring, biphenyl, bicyclohexyl,

Rd = alkyl, alkyloxy, alkanoyloxy, alkoxyalkyl, alkenyl, alkynyl, alkenyloxy, alkynyloxy, alkadienyl, alkadienyloxy, haloalkyl, haloalkyloxy,

R * = chiral group, preferably 1-methylpropyl, 1-methylbutyl, 1-methylpentyl, 1-methylhexyl, 1-methylheptyl, 1-methyloctyl, 1-methylnonyl, 2-methylbutyl, 2 Extended groups such as methylpentyl, 1-ethylheptyl, 1-trifluoromethylheptyl, etc.]

For nematic liquid crystal base mixtures, nematic compounds of all structures can be used. Usually, the following compounds (2-1) to (2-190) can be used effectively.

[Wherein R1, R2 are typical groups for alkyl, alkyloxy, alkenyl, alkynyl and other liquid crystals]

Although all kinds of nematic liquid crystals can be applied to the present invention, the liquid crystal substrate mixture should preferably not have an optical absorption band in the irradiation light conversion region between the two states. Since the preferred conversion is carried out with ultraviolet light, in particular non-aromatic liquid crystal substances, preferably compounds of the general formulas (2-191) to (2-227) below are useful.

[Wherein R 1, R 2 = alkyl, alkyloxy, halogen, cyano and other liquid crystalline groups,

m, n = independently 0-10]

Liquid crystals of these general formulas are already known and described in the literature. Compounds of this type do not show optical absorption in the near ultraviolet region.

As the base mixture, nematic discotic materials (discotic materials are listed in LiqCryst, Database of Liquid Crystalline Compounds for personal Computers, V. Vill, Hamburg 1995). Nematic discotic compounds usually have a relatively high cleaning temperature and therefore require a multicomponent mixture. Discotic nematic materials are particularly compatible with steric dense chiral olefins.

The following compounds (3-1) to (3-11) are discotic materials suitable for the present invention.

[Wherein Re is an alkyl chain wherein one or two methylene moieties may be substituted with O, C═O, S, CH═CH, C≡C, and one or two hydrogen may be replaced with CN or a halogen atom or Represents a halogen atom,

Z represents OCO, CH ₂ CH ₂ , C≡C, CH ₂ O, OCH ₂ , CH ₂ S, SCH ₂ , NHCO, OCOCH ₂ , OCOCH = CH, CH ₂ OCO, N = N.

Example 1

Preparation of Chiro-Optic Devices Using Hybrid Cells and Liquid Crystal Mixtures

99.9% by weight nematic mixture (65 mol% 4-butylcyclohexanecarboxylic acid + 35 mol% 4-hexylcyclohexanecarboxylic acid, purification temperature = 91 ° C., Δn = 0.02) showing nematic phase at room temperature and A cholesteric mixture consisting of 0.1% by weight of a chiral compound represented by the following formula (1-1) (wherein Ra = hydrogen, Rb = dimethylamino, Rc = nitro, X1 = X2 = sulfur) is prepared. The cholesteric mixture is filled into a hybrid in which the liquid crystals are aligned in parallel along one glass and perpendicular to another glass, as shown in FIG. 1. The two polarizers are adjusted at appropriate mutual angles to obtain kiro optical cells showing the dark state. As shown in Scheme 1, two stable repetitive, dark and bright states are obtained by irradiating light having two different wavelengths (435 nm / dark state, 365 nm / bright state).

Example 2

Fabrication of Holographic Recording Systems

Perform a holographic arrangement as shown in FIG. Here BS denotes a beam splitter and the liquid crystal cell is filled with the cholesteric mixture obtained in Example 1. The laser beam with a wavelength of 435 nm is split into two beams, one of which is modulated with a modulator. Within the liquid crystal device, the two beams interfere with each other to produce a hologram containing information. The information can be erased by irradiation with light of wavelength 365 nm.

Example 3

Preparation of Chiro-Optic Devices Using Liquid Crystal Mixtures and Hybrid Cells Containing Azo Compounds

A mixture of 65 mol% 4-butylcyclohexanecarboxylic acid + 35 mol% 4-hexylcyclohexanecarboxylic acid is nematic with a washing temperature of 91 ° C. This mixture does not absorb light in the visible or near-ultraviolet region. To the mixture is added 1 mol% of (S) -4-ethoxy-4 '-(2-methylbutyl) azobenzene to form a cholesteric material. This mixture is placed in a hybrid cell in which the liquid crystals are aligned parallel along one glass and vertically aligned with respect to another glass, as shown in FIG. 1. The cis isomer of the azo compound is formed by irradiation with light having a wavelength of 350 nm. Trans isomers are formed by irradiation with light in the wavelength range of 400 to 500 nm. By alternating illumination with one of these preference areas, information can be recorded and erased.

Example 4

Preparation of Holographic Recording System Using Mixtures Containing Azo Compounds

The holographic arrangement is made as described in Example 2. The liquid crystal cell is filled with the mixture prepared in Example 3. The laser beam having a wavelength of 350 nm is divided into two beams, one of which is controlled by a modulator. In a liquid crystal device, the two beams interfere with each other to produce a hologram containing information. By irradiating with light having a wavelength of 400-500 nm, information can be erased.

Example 5

Preparation of Chirooptic Devices Using Hybrid Cells and Discotic Liquid Crystal Mixtures

2,3,4,5,6-pentakis (2- (4-pentylphenyl) ethynyl) -1- (11-hydroxyundecyloxy) benzene 40 mol% and 2,3,4,5,6 A nematic discotic mixture consisting of 15 mol% pentakis (2- (4-pentylphenyl) ethynyl) -1- (10-ethoxycarbonyldecyloxy) benzene is prepared. Such compounds are described in [D. D. Janietz, K. K. Praefcke and D. Synthesized according to Singer (D. Singer, Liq. Cryst., 13 (2), 247 (1993)) 99.9% by weight of the prepared nematic discotic base mixture and a chiral compound represented by formula I (wherein Ra = Hydrogen, Rb = dimethylamino, Rc = nitro, X1 = X2 = sulfur) to prepare a nematic discotic mixture consisting of 0.1 wt.% Of the nematic discotic mixture, as shown in FIG. Charged in a hybrid aligned parallel along the glass and vertically aligned with respect to another glass By adjusting the two polarizers at appropriate mutual angles, a chiro optical cell is obtained showing the dark state, irradiated with light having two different wavelengths. This results in two stable repeating states, a dark and a bright state.

Example 6

Fabrication of Holographic Recording Systems Using Nematic Discotic Mixtures

Perform a holographic arrangement as shown in FIG. The liquid crystal cell is filled with the discotic mixture obtained in Example 5. The laser beam with a wavelength of 435 nm is split into two beams, one of which is modulated with a modulator. Within the liquid crystal device, the two beams interfere with each other to produce a hologram containing information. By irradiating with light of 365 nm wavelength, information can be erased.

Claims (8)

Between two stable states of different chirality, which contain a mixture of a suitable chiral material and nematic liquid crystal, and by irradiating light of two different wavelengths, the chirality of the mixture corresponds to two states of differing optical properties, useful for the storage of information. A device, which can be converted reversibly. 2. A chiral nematic mixture according to claim 1, wherein the chiral nematic mixture is present between two flat glass or plastic plates, the director is oriented parallel in one plate and vertically in the other plate (hybrid cell), the device being two Positioned between two polarizers. 2. The apparatus of claim 1, wherein information is holographically recorded by use of a split laser beam. The device of claim 1, wherein the nematic consists of non-aromatic calamitic (rod) molecules. The device of claim 1, wherein the nematic consists of nematic discotic molecules. The device of claim 1 wherein the chiral material consists of sterically dense olefins. The device of claim 1, wherein the chiral material consists of a chiral azo compound. A nematic liquid crystal mixture consisting of a chiral compound and a nematic liquid crystal, useful for the device of claim 1.