Cholesterol-based unsymmetrical Schiff's base dimer terminated with 4-alkoxy-5-phenylthiophene unit: synthesis and characterisation

Abstract

A series of unsymmetrical cholesterol based dimers have been synthesised and characterised. All the dimers possess a cholesterol unit connected with a 4-alkoxy-5-phenylthiophene unit through Schiff's base linkage. The length of the terminal alkyl and the alkyl spacer has been varied. All the dimers exhibit mesomorphism. Four dimers possess only the cholesteric (chiral nematic, N*) phase. One of the dimers showed smectic A (SmA) and N* phases whereas the other dimer displayed SmA, smectic chiral C (SmC*), N* and twist grain boundary (TGB) phases.

Keywords:

• thiophene
• dimers
• SmA
• SmC*
• N*
• TGB phase
• HRXRD

Acknowledgements

We thank the DST (New Delhi) and the CSIR (New Delhi) for financial assistance. Two of us (T.G. and S.C.) are grateful to the CSIR (New Delhi) for their research fellowships. We are grateful to Dr C.V. Yelamaggad for molecular modelling of the compound 10c reported in this publication.