OPTICALLY ACTIVE DIESTERS OF AROMATIC TRICYCLIC ACIDS AS CHIRAL COMPONENTS FOR MESOMORPHIC FERROELECTRICS

Optically active compounds of the formula in which the rings A, B and C independently of one another denote 1,4- phenylene which is unsubstituted or substituted by halogen, cyano, methyl and/or methoxy and in which optionally 1 or 2 CH groups are replaced with nitrogen; R represents the radical of an optically active terpene alcohol after elimination of the hydroxyl group or represents a group -(CH2)m-CHX -R ; R represents the radical of an optically active terpene alcohol after elimination of the hydroxyl group or represents a group -(CH2)n-CHX -R ; m and n independently of one another represent the numbers 0 or 1; C designates a chiral carbon atom; X and X independently of one another represent fluorine, chlorine, cyano, methyl or methoxy; R and R independently of one another designate a group R, phenyl or R-substituted phenyl, with the proviso that R differs from X and R differs from X ; R denotes an alkyl group in which a methylene group is optionally replaced with oxygen and/or a group CH-CH is optionally replaced with a group C=C; with the proviso that R and R do not simultaneously designate 2-alkyl when the rings A, B and C together represent p-terphenyl, and liquid crystalline mixtures and the use for electro- optical purposes.