Synthesis and mesomorphic properties of -methylstilbene-based liquid crystals

Abstract

Six series of -methylstilbene-based liquid crystals, i.e. 4-(4-alkylphenyl)-4'-amino--methylstilbenes (2a-e), 4-(4-alkylphenyl)-4'-cyano--methylstilbenes (3a-e), 4-(4-alkylphenyl)-4'-isothiocyanato--methylstilbenes (4a-e), 4'-(trans-4-alkylcyclohexyl)-4-fluoro--methylstilbenes (5a-e), 4'-(trans-4-alkylcyclohexyl)-4-amino--methylstilbenes (7a-e) and 4'-(trans-4-alkylcyclohexyl)-4-isothiocyanato--methylstilbenes (8a-e) were synthesised. All of these -methylstilbene-based compounds exhibit an enantiotropic nematic phase. Some of the 4-(4-alkylphenyl)-4'-isothiocyanato--methylstilbenes with longer alkyl chains exhibit a smectic A phase. All of the liquid crystals obtained exhibit a wide nematic range and high birefringence of 0.16-0.46. Both series of isothiocyanato-based, liquid crystal compounds 4a-e and 8a-e containing -methylstilbenes revealed much lower melting points and clearing temperatures than their cyano and amino homologues.