The synthesis and mesogenic behaviour of the first series of low molar mass thieno[3,2-b]thiophene-2-carboxylate ester-based mesogens

Abstract

The synthesis of a family of alkyl 5-(4-hexyloxyphenyl)thieno[3,2-b]thiophene-2-carboxylate liquid crystals is described. The synthetic methodology utilised includes a Fiesselmann synthesis of the thieno[3,2-b]thiophene core, and the first report of a completely regioselective α-bromination of the resulting thieno[3,2-b]thiophene-2-carboxylate ester. The target materials display enantiotropic smectic A phases with melting points and transition temperatures that are significantly higher than their phenyl analogues. The synthesis and mesomorphic behaviour of these new materials is reported and discussed.

Keywords:

• thieno[3,2-b]thiophene
• esters
• smectic A
• high polarisability

Acknowledgements

Financial support from Kent State University is gratefully acknowledged. We would like to thank Dr. Mahinda Gangoda for assistance in obtaining some of the NMR spectra and Dr. Robert J. Twieg for use of his DSC instrument.