Synthesis and characterization of azo benzothiazole chromophore based liquid crystal macromers: Effects of substituents on benzothiazole ring and terminal group on mesomorphic, thermal and optical properties

A series of azo benzothiazole chromophore based liquid crystalline compounds having different substituents at the sixth position on benzothiazole moiety with methacrylate terminal group were synthesized and characterized by FTIR, 1H and 13C NMR. TGA investigations showed synthesized compounds were thermally stable. POM and DSC studies revealed that all the compounds showed liquid crystal behaviors. SAXS analysis exposed that all the investigated compounds exhibited lamellar structure. Compound with H at the sixth position on the benzothiazole ring revealed only smectic liquid crystal phase whereas compounds with CH3, OCH3 and OC2H5 groups showed both nematic and smectic liquid crystal phases. The formation of mesophases as well as temperature ranges of mesophases was greatly influenced by the sixth position electron pushing substituent on benzothiazole ring as well as terminal methacrylate group. The absorption maxima (λmax) of UV–vis spectra were bathochromically shifted with the replacement of sixth position hydrogen atom by the electron donating groups on benzothiazole chromophore. Macromer with OCH3 substituent exhibited highest fluorescence emission than other compounds.