T-shaped non-symmetrical twin liquid crystalline compounds

Abstract

New unconventional T-shaped non-symmetrical dimeric liquid crystalline compounds have been synthesised and their thermotropic properties studied on the hot-stage of a polarising microscope. These compounds consist of an azo-ester mesogenic unit with a range of terminal substituents (–CH₃, –OCH₃, –NO₂ or –Cl) at one end, interconnected by a flexible spacer (n = 4, 5 or 10) via ether and ester linking units to a biphenyl moiety at the lateral hydroxyl position of the azo-ester. All the compounds were characterised using a combination of elemental analysis and standard spectroscopic methods. The compounds were found to exhibit enantiotropic nematic and smectic mesophases. The effect of different terminal substituents on mesomorphism is discussed.

Keywords:

• azo-ester
• ether–ester linkage
• flexible spacers
• T-shaped
• non-symmetrical dimers
• smectic A

Acknowledgements

One of the authors (M.C. Varia) is grateful to Professor V.A. Raghunatha for helpful discussions and assistance with the X-ray measurements. The help given by Mrs Vasudha in analysing the X-ray diffraction results is also gratefully acknowledged.