Synthesis and characterization of a new series of liquid crystal compounds derived from isoxazoles

Two homologous series of phenylisoxazoles derived from 3-[4-(4-trans-n-heptylcyclohexyl)phenyl]-5-(4-alkoxyphenyl)isoxazole and 3-[4-(4-trans-n-heptylcyclohexyl)phenyl]-5-(5-nalkylthiophene)isoxazole have been synthesized. The liquid crystal compounds obtained were characterized by NMR, differential scanning calorimetry (DSC), and optical polarized microscopy (POM). The properties of the liquid crystalline phase were investigated as a function of terminal units and type of core aromatic rings. It was found that (1) the phase transition temperature decreased with the change of core aromatic rings from phenyl for thienyl, and (2) the types of mesophase formed by these compounds do not depend on the length of the terminal chain. Thermotropic nematic and smectic phases were observed.