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.

Keywords:

• azo
• ester
• cinnamate
• smectic
• nematic
• mesophase
• naphthalene
• cyano
• fluoro

Acknowledgements

We are grateful to Dr R.A. Vora for giving valuable suggestions. We are also grateful to the Department of Applied Chemistry, Faculty of Technology and Engineering, M.S. University of Baroda, Vadodara for providing us with an optical polarising microscope for the mesophase study, Dr Parimal Paul, Department of Chemistry, C.M.C.R.I. (Central Salt and Marine Chemicals Research Institute), Bhavnagar, for their support in mass spectral analyses and Mettler Todelo, India Pvt. Ltd., Powai, Mumbai for their support with the DSC analyses.

Notes

^†This paper was presented at the 17th National Conference on Liquid Crystals held at the Department of Chemistry, V. N. S. G. University, Surat, Gujarat, India on 15–17 November 2010.