Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1986-10-30
1988-09-06
Gron, Teddy S.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
25239901, 25229963, 25229964, 350350R, 350350S, 560 1, 560 59, 560 73, 560102, 560105, 560108, 560126, 560138, 560141, 558370, G02F 110, C09K 1912, C07C 6976
Patent
active
047691760
DESCRIPTION:
BRIEF SUMMARY
This invention relates to esters, and to liquid crystal materials and devices containing them. More specifically the invention relates to ferroelectric liquid crystals.
Ferroelectric behaviour is observed in liquid crystals which exhibit a chiral tilted smectic phase, eg the smectic C, F, G, H, I, J and K phases (hereinafter abbreviated to S.sub.c * etc, the asterisk denoting chirality). The use of such liquid crystals in rapidly switched electro-optical devices, eg data processing and large screen displays, has been proposed, eg by N A Clark and S T Lagerwall, App Phys. Lett. 36, p 899 (1980), (Reference 1).
A number of properties are desirable in a liquid crystal material for use in such applications. In particular the material should exhibit its chiral tilted smectic phase over a large temperature range centred around its intended working temperature; the material should have a low viscosity (which is why the S.sub.c * phase is preferred, being the most fluid); and the material should have a high spontaneous polarisation coefficient (Ps) in its chiral tilted smectic phase. Other desirable properties include chemical stability, transparency, and the appearance of an S.sub.A phase at a temperature above the chiral phase, to assist alignment of the molecules of the material with device substrates (as described below).
Although some single compounds exhibit chiral tilted smectic liquid crystal phases with many of the desirable properties mentioned above, it is more common for a ferroelectric liquid crystal material to consist essentially of a mixture of two components, each of which may themselves be single compounds or mixtures of compounds. In such a mixture, a first component, a "host" may be selected which exhibits a tilted but non-chiral smectic phase over a broad temperature range, and with this is mixed a second component, a "dopant" which is optically active (ie contains an asymmetrically substituted carbon atom) and which induces the tilted smectic phase exhibited by the mixture to be chiral, preferably with a high Ps. Alternatively, a host may itself exhibit a chiral smectic phase but with a small Ps, and the presence of the dopant may induce an increased Ps. The presence of the dopant may additionally improve other properties of the host, eg the melting point of the mixture will often be lower than that of any of the compounds it contains, if a eutectic mixture is formed.
Research is at present being carried out to identify compounds and mixtures of compounds which are suitable for use in "host-dopant" ferroelectric smectic liquid crystal materials. It is an object of the present invention to provide novel and improved compounds for use in such materials, primarily but not exclusively as hosts, and to provide novel and improved mixtures containing them.
According to the present invention in a first aspect, there is provide a novel compound for use in a liquid crystal mixture, the compound having the Formula IA below: ##STR1## wherein ##STR2## represents ##STR3## R.sub.1 represents C.sub.3-12 alkyl; alkoxy, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy, j is 0 or 1, R.sub.2 represents C.sub.3-12 alkyl or alkoxy, one of Q.sub.1 or Q.sub.2 is H and the other F, provided that when j is 0 and ##STR4## is ##STR5## and both R.sub.1 and R.sub.2 are n-alkyl then the total number of carbon atoms in R.sub.1 and R.sub.2 is more than 12.
Compounds of Formula IA and certain related compounds have been found to be exceptionally useful components of liquid crystal mixtures as will be discussed herein.
According to the present invention in a second aspect, there is provided a novel liquid crystal material which exhibits at room temperature a smectic phase of a kind which in the presence of an optically active compound is a tilted chiral smectic phase, and which comprises a mixture of compounds at least one of which is of Formula I below: ##STR6## wherein ##STR7## represents ##STR8## j is 0 or 1 R.sub.1 represents alkyl, alkoxy, alkylcarbonyloxy, alkoxycarbonyl, or alkoxycarbonyloxy, each of Q.sub.1, Q.sub
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Bishop David I.
Bradshaw Madeline J.
Jenner John A.
Raynes Edward P.
Sage Ian C.
Gron Teddy S.
The Secretary of State for Defence In Her Britannic Majesty's Go
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