Effect of polar group on the 2,3,4-trihydroxy benzonitrile based liquid crystals trimers

Abstract

In this paper, we discuss the effect of different terminal polar groups attached to biphenyl units of 2,3,4-trihydroxy benzonitrile-based trimers on the mesomorphic properties. The thermal properties of two new series namely 2,3,4-tris-[omega-(4-fluorobiphenyl-4'-yloxy)alk-1-yloxy]benzonitrile and 2,3,4-tris-[omega-(biphenyl-4'-yloxy)alk-1-yloxy]benzonitrile were compared with cyano-substituted analogous which was previously reported. Two new trimers, which are fluoro- and hydrogen-substituted compounds were synthesised by etherification of 4-fluoro-4'-(n-bromoalkane-1-yloxy)biphenyl or 4-(n-bromoalkane-1-yloxy)biphenyl with 2,3,4-trihydroxy benzonitrile under basic conditions. Polarising optical microscope and differential scanning calorimeter were used for the characterisation of mesogenic properties. The small- and wide-angle X-ray scattering (SAXS and WAXS) measurements show the formation of intercalated trimers in the nematic (N) phase. This study enables to understand the influence of terminal polar groups on the liquid crystalline behaviour of trimers in a non-conventional molecular design.