Synthesis and mesomorphic properties of new rod-like heterocyclic liquid crystals

Structure-property relationship is one of the most important research areas in the liquid crystals. Therefore, in the present work, we studied a new series of rod-like heterocyclic liquid crystals, 6-methyl-2-[4-(4alkoxybenzoyloxy)benzylideneamino]benzothiazoles. The rod-like molecules having heterocyclic and two phenyl rings as core system, imine and ester as linking units, long alkoxy chain at the terminal position. There are six members in the series with different length of alkoxy chain (CnH2n+1O-, where n = 6, 8, 10, 12, 14, 16). The structures of the compounds were elucidated using spectroscopic techniques. Their mesomorphic behaviours were determined by differential scanning calorimetry, polarizing optical microscopic and powder X-ray diffraction techniques. Members with shorter alkoxy chain (n = 6, 8, 10) exhibited single mesophase (nematic). As the alkoxy chain increased to n = 12, 14, 16, the nematic phase appeared together with an additional mesophase (smectic). The phase width was dependent on the alkoxy chain length. The incorporation of the methyl substituent at the sixth position (lateral) of the benzothiazole able to increase the clearing point and widen the mesophase width of the compounds. Keywords: benzothiazole, Schiff base, nematic, smectic A