A material of general formula I: ##STR1## where E=0 indicates a non-cyclic system, and E=1 indicates a cyclic system;G is R.sub.3 SiR.sub.1 R.sub.2 (O).sub.kR.sub.1, R.sub.2, R.sub.3 are independently selected from C.sub.1-16 alkyl which may be partly or fully halogenated, H and formula IA: ##STR2## wherein Y is a propylene group which may be partially halogenated with fluorine or chlorine and Y.sub.1 is independently selected from COO, OCO, O, S, CHOH, CHF, CO or CH.sub.2 ;Q and Q.sub.1 are independently selected from (CH.sub.2).sub.n wherein one or more non-adjacent methylenes may be replaced by O andn=0-20;Z and Z.sub.1 are independently selected from O, S, single covalent bond, COO or OCO; ##STR3## represents a mesogenic group and is given by the general structure II ##STR4## A, B, D are selected from the following rings: ##STR5## the above rings may be substituted with one or more of the following substituents in at least one of the available substitution positions: F, Cl, Br, CH.sub.3, CN, OR, R or NCS where R is a C.sub.1-5 branched or straight chain alkyl provided that the total number of rings present is not greater than 4; and W.sub.1 and W.sub.2 are independently COO, OCO, single bond, CH.sub.2 CH.sub.2, CH.sub.2 O, OCH.sub.2, O, S, CH.dbd.CH, C.tbd.C, or N.dbd.N.