Synthesis and characterization of ferroelectric liquid crystal dimers containing thioester and carboxylate linking groups in the inner side of the molecule

A homologous series of chiral unsymmetrical liquid crystal dimers possessing carboxyl and carbothiol linkages nearer to the chiral center were synthesized using (S)-2-(6-methoxynapthyl-2) propionic acid as chiral starting material. All the dimers were characterized by usual spectral techniques, thermal methods and electro-optical studies. Structural effects on the mesomorphic and physicochemical properties were investigated in terms of variation of achiral chain length at both terminals and compared with our previous investigations that contain both carboxylate and both carbothiloate linkages.The microscopic investigation reveals that these dimeric compounds exhibit only SmC∗ and SmA∗ mesophases. The liquid crystalline behaviour of the dimers was further confirmed by DSC analysis. It was observed that the SmC∗ phase range is increased significantly with increase in the achiral chain length. Whereas SmA∗ phase range decreases with increase in achiral chain length. When comparing the mesomorphic behaviour of LC dimers containing –COO– and –COS– linkages, the present compounds do not exhibit metastable states but increased SmA∗ and SmC∗ mesophase stability. The spontaneous polarization (Ps) and tilt angle values were also measured and a largest of 40.8 nCcm−2 and 44.5 deg were obtained, respectively.