A new series of liquid-crystalline bi-1,3,4-oxadiazole derivatives: synthesis and mesomorphic behaviour

Symmetrical bi-1,3,4-oxadiazole derivatives, namely 5,5'-bis(phenyl-4-alkoxybenzoate)-2,2'-bi-1,3,4-oxadiazole (BBOXD-n, n=6, 10, 14, 16), were synthesised. All BBOXD-n exhibited remarkably stable SmC phases by virtue of the high transition enthalpies of SmC-I. In addition, BBOXD-6 and BBOXD-10 showed an enantiotropic nemetic phase with enthalpies of the N-I transition up to 5.16 kJ mol(-1). As confirmed by wide-angle X-ray diffraction analysis and MM2, molecules of BBOXD-n showed high-angle tilting (55-57 degrees) within their smectic C phases.