Effects of lateral methyl and terminal substituents on thermal, mesomorphic and optical properties of azo-ester mesogens

Abstract

Four azo-ester mesogens with lateral methyl were synthesized where these compounds are differed by the terminal substituents i.e. –H, –Cl, –Br and –CN. The compound with -H terminal substituent displayed nematic behavior with narrow mesophase range while electron-withdrawing groups terminated compounds exhibited mesophase behavior with wider nematic range. The presence of lateral methyl group and different terminal substituents used in this study could be utilized to generate anticipated mesophase. Their mesogenic behavior was also compared with previously investigated analogues and other structurally related series to evaluate the effect of lateral methyl group on the mesomorphism. Optical investigations demonstrated that their absorption spectra are identical in shape because of the structural similarities in the mesogenic unit whereas the fluorescence spectra exhibited blue emission and were red-shifted with the incorporation of terminal substituents. The synthesized azo-ester compounds could be potential candidate as fluorescent materials for practical applications such as organic light-emitting diode applications.