New semi-rigid thermotropic liquid crystalline (LC) polyesters composed of quarterphenyl analogue of 2,2 ' -bis(1,3,4-thiazole) were synthesized by high-temperature solution polycondensation of a dioxydiundecanol derivative of 5,5 ' -diphenyl-2,2 ' -bis(1,2,4-thiadiazole) with four diacyl chlorides, whose structures were characterized by FT-IR and (NMR)-N-13 spectroscopy, as well as elemental analysis. Differential scanning calorimetry (DSC) measurements and texture observations using polarizing microscopy displayed that all the polymers from 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 ' -dis(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 were 3.67-2.82 eV.