Liquid crystal compounds

摘要

A compound of formula (I): where R¹ is alkyl or alkenyl, Y¹ and Y² are independently selected from oxygen or sulphur, n is an integer of from 1 to 5, A is an optionally substituted phenyl or an optionally substituted cycloalkyl ring, X is a direct bond, a C_1-4alkylene, a C_2-4alkenylene, an acetylene, -CO(O)- or a group of sub-formula (i): where X¹ and X² are independently selected from a direct bond, a C_1-4alkylene, a C_2-4alkenylene, an acetylene, -CO(O)- and R², R³ and R⁴ are independently selected from hydrogen, halo or cyano, provided that no more than one of R², R³ and R⁴ is hydrogen. These compounds have a high dipole moment and may be used as dopants in liquid crystal mixtures.