Liquid Crystal Phase Characterizations of b-Diketone, Pyrazole and Isoxazole Biphenyl Derivatives

Abstract

In this report, 3 types of compounds, e.g., b-diketones, pyrazoles and isoxazoles were synthesized, three of each, and their properties investigated, for the total of 9 compounds. Generally, most of the b-diketone derivatives exhibited simple melting behavior, with some exceptions of a single short range smectic A phase. The long and flexible alkyl chain might result in this observation that it expelled the neighbor molecule away thus a smectic A was formed. In contrary, an oxygen atom in some types of compounds might raise intermolecular interaction and the molecules are too close together to form any mesophases. When pyrazoles were formed, four compounds exhibited mesophases while two were non-mesogenic. In starting materials, the b-diketone moieties are rather flexible even with an intramolecular hydrogen bond, however, the pyrazole moieties are more rigid and various mesophases were observed. As of isoxazoles, the moesophase trends were similar to those of the pyrazoles, except with higher transition temperatures of the formers. Nevertheless, the isoxazoles were non-mesogenic.