Cyanohyorin derivatives and their use in liquid crystal material

Details Cyanohyorin derivatives and their use in liquid crystal material Cyanohyorin derivatives and their use in liquid crystal material

1990-07-11

1992-07-28

Stoll, Robert L.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229901, 25229966, 25229967, 560 59, 560 65, 560 73, 560 76, 560 83, 560 85, 560102, 560109, 560108, C09K 1912, C09K 1952

Patent

active

051338963

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to cyanohydrin derivatives and also to liquid crystal materials containing them. In particular the invention relates to chiral derivatives and ferroelectric smectic liquid crystal compositions containing them.
2. Description of the Prior Art
Ferroelectric smectic liquid crystal materials are known, (e.g. N A Clark et al: Appl Phys Lett (1980) 36 899), and exploit the electro-optical properties of the ferroelectric chiral smectic phase. The chiral smectic C (abbreviated S*.sub.C the asterisk denoting chiralty) is most used as it is the most fluid, but other chiral smectic phases e.g. I, F, J, K. G, H or X may also be used.
Although some ferroelectric smectic liquid crystal materials are single compounds it is more usual for such a material to be a composition. Generally such a composition contains one or more compounds which either singly or together show an S.sub.C phase (termed a smectic "host"), together with one or more chiral (i.e. optically active) compounds which are generally added to induce the smectic material to show a high spontaneous polarisation. Ps. The composition may also contain additives. For example to broaden the Sc* range, to suppress undesirable phases, or optically active compounds to modify the helical pitch of the Sc* phase.
Among the features sought in a good ferroelectric smectic liquid crystal material are low viscosity, fast switching speeds, a broad Sc* phase range, and a high spontaneous polarisation coefficient Ps and a long helical pitch. In view of the high cost of synthesis of optically pure compounds it is also desirable that the chiral compound is cheap.
Optically active compounds used in ferroelectric smectic liquid crystal compositions generally consist of a "core" consisting of a chain of linked cyclic groups, with an optically active group containing an asymmetric carbon atom at or near a terminal position of the chain. The core is selected from the reasonably well known combinations of cyclic groups which encourage the compound to be miscible with smectic liquid crystal phases. The goal of much research in ferroelectric smectic liquid crystal chemistry is to identify novel optically active groups which may be combined with such cores to form advantageous compounds.
Many suitable optically active compounds are known.
PCT/GB 87/00441 (Agents Ref P0383) are JPA-61-243055 describe compounds of structure ##STR1## where R is alkyl. These compounds show a high Ps. PCT/GB87/00441 has a publication date later than the priority date of this application.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide novel compounds which are suitable optically active constituents of ferroelectric liquid crystal compositions, and which have advantageous properties relative to known compounds.
This invention provides compounds which are novel cyanohydrin derivatives having a general formula I: ##STR2## wherein R.sup.1 is selected from hydrogen, C.sub.1 -C.sub.12 alkyl, alkoxy, perfluoroalkyl and perfluoroalkyl and may be straight chain or branched chain; R.sup.2 is alkyl, which may be C.sub.1 -C.sub.8 straight chain, C.sub.1 -C.sub.15 branched chain or cyclic; r is an integer 1 to 10, n and m are independently 0 or 1; with the provisos that:
if both n and m are O then X is selected from: ##STR3## wherein the (F)'s indicate that X carries one or two fluorine substituents in any one or two of the available lateral substitution positions on the indicated phenyl ring, p is 0 or 1, Z is a single bond where p is 0 and COO when p is 1, and;
if one or both of n or m are 1 then X is a group of general formula: ##STR4## where each Ring A, B and C is independently selected from phenyl, fluoro or chloro substituted phenyl, cyclohexyl, pyrimidyl, pyridyl or dioxanyl, each link A, B and C is independently a single bond, COO, OOC, CH.sub.2 CH.sub.2, CH.dbd.N, N.dbd.CH, CH.sub.2 O, OCH.sub.2 or O , and each of a, b and c is 0 or 1 provided (a+b+c) is 2 or 3.


DESCRIPTION OF PREFERRED EMBODIMENTS

Th

REFERENCES:
patent: 4725688 (1988-02-01), Taguchi et al.
patent: 4753752 (1988-06-01), Raynes et al.
patent: 4780241 (1988-10-01), Furukawa et al.
patent: 4780242 (1988-10-01), Miyazawa et al.
patent: 4876026 (1989-10-01), Saito et al.
patent: 4911863 (1990-03-01), Sage et al.
JP-63233932 English Abstract and p. 300 compound 162, Sep. 28, 1988.

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