Phthalonitrile derivatives are represented by the formula (I):
wherein X and Y each represents a C1-9 alkyl or alkoxy group, The compounds are prepared by cyclisation reaction of a butadiene derivative X-CH=CH-CH-CH-Y with fumaronitrile or dicycanoacetylene, followed by oxidation or bromination. The compounds have a large negative dielectric anis- tropy, and wide liquid crystal range, and are useful, alone or with other liquid crystals, in liquid crystal display devices.
wherein R represents H,
or a halogen atom, where m is an integer of 1 to 9 and n is 0, 1 or 2, but at least one of X and Y does not represents a methyl group, and Y does not represent an alkyl or alkoxy group when X represents
and R' represents an alkyl group.