The Thermal Properties of Liquid Crystalline Materials Incorporating Cyanothiophene and Cyanofuran

Some homologous series of cyanothiophene and cyanofuran compounds have been prepared. 4-Alkoxyphenyl 3-(5-bromo-2-thienyl)acrylate (1) and 4-alkoxyphenyl 3-(5-cyano-2-thienyl)acrylate (2), and 4-alkoxy-phenyl 4-(5-bromo-2-furylcarbonyloxy)benzoate (3) and 4-alkoxyphenyl 4-(5-cyano-2-furylcarbonyloxy)benzoate (4) give rise to a nematic phase. For compound 4, a smectic A phase which commences from the hexyloxy homolog has a bilayer (SA2) arrangement of the molecules. The thermal stabilities of the mesophases are lower than those of the corresponding benzonitrile compounds. This arises from an increased molecular breadth around the terminal portion and the change of the dipole moment arising from the terminal cyano group bending with respect to the long molecular axis.