Liquid crystal compounds

Abstract

Novel liquid crystal compounds are disclosed, which are chiral esters based upon the phenol ##STR1## Typical examples are: ##STR2## and mixtures of these compounds have a helical pitch such that the mixtures reflect light of a specific wavelength when illuminated with ordinary light and the pitch is temperature sensitive so that the mixtures can be used in temperature indicating devices. Specific examples are given as are samples of mixtures that can be used in phase change electro-optic display devices.

We claim: 
     
       1. A liquid crystal compound which is an optically active ester having the formula: ##STR35## wherein X is ##STR36## R is an alkyl group, which may be chiral, having less than 15 carbon atoms, Y 1  is halogen or methyl and Y 2  is halogen or methyl. 
     
     
       2. A liquid crystal compound as claimed in claim 1 and wherein X is: ##STR37## 
     
     
       3. A liquid crystal compound as claimed in claim 1 and wherein X is: ##STR38## 
     
     
       4. A liquid crystal compound as claimed in claim 3 and wherein Y 2  is chlorine and R is 2-methylbutyl. 
     
     
       5. A liquid crystal compound as claimed in claim 1 and which is prepared by reacting on optically active substituted phenol compound having the formula: ##STR39## with an acid chloride having the formula X-COCl where X is as defined in claim 1 has the same meaning as R in claim 1. 
     
     
       6. A liquid crystal compound as claimed in claim 5 and wherein the optically active substituted phenol compound is prepared by hydrolyzing a corresponding methoxy compound: ##STR40## has the same meaning as R.[.*.]. in claim 5; said methoxy compound being prepared by the reaction of ##STR41## 
     
     
       7. A liquid crystal compound as claimed in claim 3 and which is prepared by reacting an optically active hydroxy benzoate compound having the formula ##STR42## with an acid chloride having the formula X-COCl where X is ##STR43## 
     
     
       8. A liquid crystal compound as claimed in claim 7 and wherein said hydroxy benzoate compound is prepared by reacting a compound ##STR44## with an optically active compound ##STR45## 
     
     
       9. A liquid crystal material which comprises a mixture of at least two compounds as claimed in claim 1, said mixture exhibiting a cholesteric mesophase suitable for use in a cholesteric-to-mesophase change electro-optic device. 
     
     
       10. A liquid crystal material which comprises a mixture of at least one compound as claimed in claim 1 together with at least one compound selected from a 4'-alkyl-4-cyanobiphenyl, a 4'-alkoxy-4-cyanobiphenyl and a 4"-alkyl-4-cyano-p-terphenyl, said mixture exhibiting a cholesteric mesophase suitable for use in a cholesteric-to-mesophase change electro-optic device. 
     
     
       11. A liquid crystal material which contains at least one compound as claimed in claim 1, said material being in the form of a thin film in the Grandjean plane texture. 
     
     
       12. In a liquid crystal device including means for containing a region of liquid crystal material, a region of liquid crystal material in said containing means, and means for applying an electrical field to said material to alter the molecular arrangement in said material, the improvement wherein said containing means contains a liquid crystal material of the formula of claim 1. .Iadd. 13. A liquid crystal material which is a mixture of liquid crystal compounds, each of which exhibits a liquid crystal phase, at least one of said crystal liquid compounds being a chiral compound existing in a state in which it is not mixed with an equal amount of its optical isomer of opposite optical rotation, said chiral compound forming at least 5 % by weight of said material and having a molecular helical pitch of about 0.5 μm or less, said chiral compound being an ester having the formula (I): ##STR46##.Iaddend. where X is selected from the group consisting of: ##STR47## where R is an alkyl group having less than 15 carbon atoms, and R 1  is an n-alkoxy or n-alkyl group having less than fifteen carbon atoms. 
     
     
        .Iadd. 14.  The material of claim 13 adapted for use in a cholesteric to nematic phase change effect electro-optical device, said material comprising nematogenic liquid crystal material as a major component and said chiral compound as a minor component. .Iaddend..Iadd. 15. The material of claim 14 and wherein said liquid crystal material has a composition such that its molecular helical pitch is of the order of 1 μm. .Iaddend..Iadd. 16. The material of claim 15 and wherein the chiral content comprises 5 to 12% by weight of said liquid crystal material. .Iaddend..Iadd. 17. The material of claim 14 and wherein the nematogenic liquid crystal material includes at least one compound selected from 4-n-alkyl-4'-cyanobiphenyls and 4-n-alkoxy-4'-cyanobiphenyls. .Iaddend. .Iadd. 18. The material of claim 14 and wherein the chiral content includes the compound ##STR48## 
     
     
       .Iaddend. where R C  is (+)-2-methylbutyl. .Iadd. 19.  The material of claim 18 and wherein the chiral content also includes the compound ##STR49## 
     
     
       .Iaddend. .Iadd. 20.  The material of claim 14 which additionally incorporates a pleochroic dye dissolved therein. .Iaddend..Iadd. 21. The material of claim 13 which has a composition such that selectivity the material has a molecular helical pitch giving selective reflection of light in the visible spectrum. .Iaddend..Iadd. 22. The material of claim 21 and wherein the chiral content has a molecular helical pitch of the order of 0.2 μm. .Iaddend..Iadd. 23. The material of claim 21 which is capable of selectively reflecting light in the visible region of the spectrum at temperatures less than 43° C. .Iaddend..Iadd. 24. The material of claim 13 having a chiral content which comprises a plurality of optically active compounds at least one of which is a compound of formula (I). .Iaddend..Iadd. 25. The material of claim 13 having a chiral content which comprises a plurality of optically active compounds, at least two optically active compounds of which have the formula (I)..Iaddend..Iadd. 26. The material of claim 13 comprising at least one compound of the formula ##STR50##.Iaddend. where R C  is (+)-2-methylbutyl and R 1  is n-alkyl. .Iadd. 
     
     
        7.  The material of claim 13 comprising at least two compounds of the formula: ##STR51##.Iaddend. where R C  is (+)-2-methylbutyl and R 1  is n-alkoxy. 
     
     
        .Iadd. 28.  The material of claim 27 wherein one of said two compounds is ##STR52## 
     
     
       .Iaddend. .Iadd. 29.  The material of claim 21, comprising three compounds of the formula ##STR53##.Iaddend. where R C  is (+)-2-methylbutyl and R 1  is n-alkoxy. 
     
     
        .Iadd. 30.  The material of claim 29 wherein one of said three compounds is ##STR54## 
     
     
       .Iaddend. .Iadd. 31.  The material of claim 29 wherein said three compounds are ##STR55## 
     
     
       .Iaddend. .Iadd. 32.  A material as claimed in claim 13, wherein the chiral compound exhibits a cholesteric liquid crystal phase and said material exists in a cholesteric state. .Iaddend.