Mesomorphic properties of liquid crystalline compounds with biphenyl moiety containing azo-ester, azo-cinnamate central linkages and different terminal group ^†

Abstract

In order to investigate the influence of the central linkage and terminal substitutions on mesophase behaviour of liquid crystalline compounds we have synthesised six homologues series viz. 4′-(naphthalen-1-yldiazenyl)biphenyl-4-yl-4-alkoxybenzoate (Series-A), 4′-[(4-cyanophenyl)diazenyl]biphenyl-4-yl-4-alkoxybenzoate (Series-B), 4′-[(4-fluorophenyl)diazenyl]biphenyl-4-yl-4-alkoxybenzoate (Series-C), 4′-(naphthalen-1-yldiazenyl)biphenyl-4-yl(2E)-3-[4-alkoxyphenyl]prop-2-enoate (Series-D), 4′-[(4-cyanophenyl)diazenyl]biphenyl-4-yl(2E)-3-[4-alkoxyphenyl]prop-2-enoate (Series-E) and 4′-[(4-fluorophenyl)diazenyl]biphenyl-4-yl(2E)-3-[4-alkoxyphenyl]prop-2-enoate (Series-F). Series-A, -B and -C have azo-ester central linkages whereas Series-D, -E and -F have azo-cinnamate central linkages and naphthalene, 4-cyanophenyl and 4-fluorophenyl as terminal groups, respectively. All these compounds were characterised by elemental analyses and spectroscopic techniques (ultraviolet-visible, Fourier transform infrared, proton and carbon nuclear magnetic resonance and mass spectrometry. Their mesomorphic properties were measured by optical polarised microscopy and differential scanning calorimetry. All the derivatives are showing enantiotropic mesomorphism.