λ-Shaped azomesogens with polar chloro- and nitro-substituents

Abstract

A new homologous series of λ-shaped mesogenic azo esters with polar chloro- and nitro- substituents has been synthesised by attaching a rigid 2-chloro-4-nitrophenylazo group to a resorcinol moiety by a central azo linkage. Both phenolic hydroxyl groups are esterified by 4-n-alkoxybenzoyl groups. All the compounds synthesised have been characterised using a combination of elemental analysis and standard spectroscopic methods. The mesomorphic properties of the compounds have been determined by polarising optical microscopy and differential scanning calorimetry. The lower members of the series are non-mesogenic, the middle members exhibit a nematic mesophase, and higher members exhibit a smectic A mesophase. The effect of polar chloro-, nitro-, and long lateral aromatic substituents, on mesomorphism is discussed.

Keywords:

• λ-shaped
• azomesogens
• smectic A
• nematic

Acknowledgements

The authors are grateful to the Dean of the Faculty of Technology and Engineering, and to the Principal of the Applied Chemistry Department, for providing research facilities.

One of us (AKP) is indebted to the University Grants Commission, New Delhi, India, for financial support via UGC Major Research Project, F 30–68/2004(SR).

Notes

This paper was presented at the 14th National Conference on Liquid Crystals, Department of Physics, University of North Bengal, Siliguri, 17–19 December 2007, and was awarded the Jawahar Lal Nayar Memorial Prize.