Synthesis and phase-transition behaviors of new symmetrical dimer liquid crystals containing benzothiazole unit

This article reports the synthesis and characterization of a series of homologous symmetrical dimers alpha,omega-bis[4-(6 '-ethoxybenzothiazol-2 '-yl)iminomethylphenoxy] alkane. Five members with different lengths of alkyl spacer groups of even parity varying from butyl (C4H8) to dodecyl (C12H24) were synthesized. Spectroscopic analysis (IR, H-1 and C-13 NMR) along with electron-ionization mass spectrometric techniques were employed to verify the molecular structures of the dimers. Differential scanning calorimeter was used for determination of the phase-transition temperature and associated enthalpy changes. Optical studies and mesophase identification were carried out using a polarizing optical microscope attached to hotstage. A diversity of phase-transition behavior was observed as the length of the alkyl spacer increased from C4H8 to C12H24. Almost all title compounds exhibited nematic phase except the dimer containing butyl spacer in which the mesomorphic property was absent.