Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1997-02-25
1998-09-01
Kelly, C. H.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
25229961, C09K 1912, C09K 1934
Patent
active
058007377
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB95/01240 filed May 30, 1996 now abandoned.
This invention relates to liquid crystal compositions and to devices incorporating such compositions. Such compositions are incorporated in liquid crystal devices (LCDs) and exhibit useful electro-optical effects, due to the fact that by application of an electric field across a thin layer of such a composition the molecules can be caused to switch between two possible states of molecular orientation and, as a result of the anisotropy of such a medium, the optical properties of the two states are different and the transmission and/or reflection of light is changed. One particular class of compositions in which both of the states are stable even in the absence of an applied field contains such a thin layer and exhibits ferro-electricity. It is with such compositions that the present invention is concerned.
It is desirable in such ferro-electric compositions to achieve a high contrast ratio and high transmissivity over as wide a temperature range as possible whilst utilising the lowest possible operating voltage. To achieve this, it is believed that the molecules comprising the composition should be in as ordered a state as possible, a property which is often measured by the so-called "relaxed cone angle" which should ideally be 45.degree.. Some success in this regard has been obtained previously by modifying the environment containing the composition, which typically comprises two parallel flat glass plates, for example by providing the so called "high surface tilt alignment layer" on the surfaces of the plates which come into contact with the composition. However, this is very difficult to apply sufficiently uniformly and consistently, which leads to low yields of product and corresponding high costs.
It is an object of the present invention to provide a ferro-electric liquid crystal composition which, in the absence of such expensive alignment layers, exhibits a high cone angle.
Accordingly we provide a composition comprising from 90% to 99.9% by weight of one or more achiral host compounds of the formula 1; ##STR4## wherein X is A.sub.1 or OA.sub.1 ; carbon atoms, optionally substituted with one or more F or CN; of Z.sub.1, Z.sub.2, Z.sub.3, and Z.sub.4 must be F; ##STR5## and from 0.1% to 10% by weight of a chiral dopant compound of the formula 2: ##STR6## wherein D.sup.1 is D (as in Formula 1) or a single bond; substituted with one or more F or CN and containing at least one centre of asymmetry; --CH(R.sub.1)COA.sub.5 A.sub.5 is OR.sub.1 or --N(R.sub.2)R.sub.3 where R.sub.2 and R.sub.3 are hydrogen, R.sub.1, phenyl optionally substituted by R.sub.1, or together form a homocyclic or heterocyclic ring optionally substituted by R.sub.1, provided that R.sub.2 and R.sub.3 are not the same; significance, except that all of Z.sub.1, Z.sub.2, Z.sub.3 and Z.sub.4 can be hydrogen.
By achiral compounds we mean compounds which are not optically active either because they possess no centre of asymmetry or because they contain a racemic mixture of the (+) and (-) forms of such enantiomers.
By chiral compounds we mean compounds which are optical active because they possess a centre of asymmetry.
Particularly useful achiral host compounds of formula 1 comprise those in which: ##STR7## either Z.sub.1 is F and Z.sub.2, Z.sub.3, Z.sub.4, are H or Z.sub.1, Z.sub.2, are H and Z.sub.3, Z.sub.4 are F;
Particularly useful chiral dopant compounds of formula 2 comprise those in which: ##STR8## or a single bond; A.sub.1 is a straight chain alkyl containing from 3 to 12 carbon atoms; Z.sub.2, are H and Z.sub.3, Z.sub.4 are F, or all of Z.sub.1, Z.sub.2, Z.sub.3 and Z.sub.4 are H; or a branched chain alkyl group possessing a centre of asymmetry or
Specific achiral host compounds of formula 1 which we have found to be particularly useful include: ##STR9##
Specific chiral dopant compounds which we have found to be particularly useful include: ##STR10##
The compounds used as achiral hosts and as chiral dopants are known and most are commercially available.
REFERENCES:
patent: 5182047 (1993-01-01), Coates et al.
patent: 5273680 (1993-12-01), Gray et al.
patent: 5316694 (1994-05-01), Murashiro et al.
patent: 5378392 (1995-01-01), Murashiro et al.
patent: 5384071 (1995-01-01), Gray et al.
patent: 5486309 (1996-01-01), Gray et al.
Central Research Laboratories Limited
Kelly C. H.
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