Nematic Mesophases in 9-Methyl and 9-Bromo-2-Fluorenyl 4-Alkoxybenzoates

Abstract

Abstract The esters, 9-methyl-2-fluorenyl 4-alkoxybenzoates with C5, C7, G9 C11, and C14 chain lengths were synthesized in order to determine the effect of the 9-substituent in the fluorene rings on their mesomorphic properties. Their structures were determined by spectroscopic methods including 1H-NMR, 13C-NMR, and 2D-COSY-NMR. All these compounds showed a nematic phase with a nematic-isotropic transition temperature between 74–100°C. The nematic phase in these materials could be supercooled to room temperature. The nematic phase also appeared in the corresponding 9-bromo esters but at higher temperatures and was enantiotropic only in one homolog, C9+. Comparisons were also made with the 7-bromo-2-fluorenyl 4-alkoxybenzoates with C7, C9 and C14 chain lengths. These compounds all yielded the smectic A phase with the nematic phase only appearing in the C7 homolog. The presence of bromine in the 7-position of the fluorenyl esters increased the liquid crystal isotropic transition temperature to about 200°C.