Ferroelectric liquid crystal composition and light switching element comprising the same

A ferroelectric liquid crystal composition comprising four components, A, B, C and D, in respective amounts of 75 to 95% by weight, 3 to 9% by weight, 3 to 12% by weight, and 2 to 5% by weight, based on the total amount of the components A, B and C and having a phase sequence series of an isotropic liquid, a cholesteric phase, a smectic A phase and a chiral smectic C phase, proceeding in that order from the high temperature side and a spontaneous polarization value of 30 nC/cm.sup.2 or less,

• said component A being at least one compound selected from the group consisting of compounds represented by the general formula (I):
• ##STR51## wherein R.sup.1 and R.sup.2 which may be the same or different are each a straight-chain or branched alkyl, alkoxy or alkanoyloxy group having 1 to 18 carbon atoms, and compounds represented by the general formula (II) ##STR52## wherein R.sup.3 and R.sup.4 which may be the same or different, are each a straight-chain or branched alkyl or alkoxy group having 1 to 18 carbon atoms,
• said component B being at least one compound selected from the group consisting of compounds represented by the general formula (III):
• ##STR53## wherein R.sup.5 is a straight-chain or branched alkyl or alkoxy group having 1 to 18 carbon atoms, R.sup.6 is a straight-chain or branched alkyl group having 2 to 18 carbon atoms or a straight-chain or branched alkoxy group having 1 to 18 carbon atoms and * represents an asymmetric carbon atom, and compounds represented by the general formula (IV):
• ##STR54## wherein R.sup.7 is a straight-chain or branched alkyl or alkoxy group having 1 to 18 carbon atoms, R.sup.8 is a straight-chain or branched alkyl group having 2 to 18 carbon atoms or a straight-chain or branched alkoxy group having 1 to 18 carbon atoms and * represents an asymmetric carbon atom,
• said component C being at least one compound selected from the group consisting of compounds represented by the general formula (V):
• ##STR55## wherein R.sup.9 is a straight-chain or branched alkyl or alkoxy group having 1 to 18 carbon atoms, R.sup.10 is a straight-chain or branched alkyl group having 2 to 18 atoms, X is --OCH.sub.2 -- or --CH.sub.2 O--, m and n are each 1 or 2, provided that M+n=3 and * represents an asymmetric carbon atom,
• said component D being at least one compound selected from the group consisting of compounds represented by the general formula (VI):
• ##STR56## wherein R.sup.11 is a straight-chain or branched alkyl or alkoxy group having 1 to 18 carbon atoms, R.sup.12 is a straight-chain or branched alkyl group having 2 to 18 carbon atoms, Y is a cyano group or a halogen atom and * represents as asymmetric carbon atom, and compounds represented by the general formula (VII):
• ##STR57## wherein R.sup.13 is a straight-chain or branched alkyl or alkoxy group having 1 to 18 carbon atoms, R.sup.14 is a straight-chain or branched alkyl group having 2 to 18 carbon atoms and * represents an asymmetric carbon atom.