Thermotropic Liquid Crystalline Polymers Having Five-Membered Heterocycles as Mesogens, 7. Synthesis and Photoluminescent Properties of Semi-Rigid Thermotropic Liquid Crystalline Polyesters Based on a Quaterphenyl Analog of 2,2′-Bis(1,3,4-thiadiazole)

Abstract

New semi-rigid thermotropic liquid crystalline (LC) polyesters composed of a quaterphenyl analogue of 2,2′-bis(1,3,4-thiadiazole) were synthesized by high-temperature solution polycondensation of a dioxydiundecanol derivative of 5,5′-diphenyl-2,2′-bis(1,3,4-thiadiazole) with four diacyl chlorides, whose structures were characterized by FT-IR and 13C NMR spectroscopy, as well as elemental analysis. Differential scanning calorimetry (DSC) measurements and texture observations using polarizing microscopy displayed that all the polyesters form stable enantiotropic smectic and/or nematic LC phases. Solution and solid state absorption and fluorescence spectra indicated that the polyesters show absorption maxima arising from the 2,2′-bis(1,3,4-thiadiazole) moiety and emit bluish green light, the Stokes shifts being 129 nm in solution and 60–64 nm in the solid state. Band gap energies of the polyesters calculated from the solid state absorption spectra were 2.67–2.82 eV.