Synthesis and mesomorphic properties of non-symmetric liquid crystal dimers stabilized by benzothiazole and substituted aromatic imines

Two new homologous series of non-symmetric liquid crystal dimers N -(4-(n-(4- (benzothiazol-2-yl)phenoxy)alkyloxy)benzylidene)-4-bromoanilines and N -(4-(n-(4- (benzothiazol-2-yl)phenoxy)alkyloxy)benzylidene)-4-methoxyanilines in which the methylene spacer of CnH2n with even parity of n ranging from 4 to 12 and the substituents of bromo and methoxy attached to respective aniline fragments have successfully been synthesized and characterized. The salient feature of these series can be attributed to the conversion of non-mesogenic units of benzothiazole and aromatic imine units to mesogens through the formation of dimers. All the title compounds exhibit enantiotropic nematic phases. The smectogenic properties also prevail among the series containing Br entity wherein the spacers are C8H16, C10H20 and C12H24. In general, the isotropization temperatures for both series were seen to descend with the increase in the spacer length. Comparison among the compounds possessing Br and OCH3 substituents shows that the anisotropic properties are governed partially by the presence of substituent residing in the aniline unit.