Non-symmetric chiral isoflavone dimers: synthesis, characterisation and mesomorphic behaviour

Abstract

A new series of non-symmetric chiral isoflavone-based liquid crystalline dimers, α-(2-methylbutyl-4′-(4″-phenyloxy)benzoate)-ω-(3-(4′-decyloxyphenyl)-4H-1-benzopyran-4-one-7-oxy)alkanes, with 3–12 carbon atoms in the alkyloxy spacer, have been synthesised. A pronounced odd–even effect for the phase transition temperatures upon varying the spacer length was observed. The short dimers exhibited monolayer smectic A (SmA) and smectic C (SmC*) phases while for longer homologues a chiral nematic (N*) phase was found. The temperature range of the nematic phase was broadened with elongation of the alkyl spacer. Stabilisation of the nematic phase resulted from competition between the monolayer and intercalated smectic structures. The SmA–SmC* phase transition was second order for all studied compounds with a cross over to the de Vries type behaviour for the shortest homologue.

Keywords:

• liquid crystals
• chirality
• non-symmetric chiral dimers
• isoflavonoids
• phase transition

Acknowledgements

The authors would like to thank Universiti Sains Malaysia for funding the project through RU Research Grant (account no. 203/PKIMIA/6711192 and 1001/PKIMIA/811140) and USM Fellowship Scheme. The Polish group wish to acknowledge the TEAM program from FNP (project TEAM/2010-5/4). The authors are also grateful to Professor Corrie T. Imrie from University of Aberdeen, Scotland for his helpful comments and discussion regarding this work.