Occurrence of a transition between two polar orthogonal smectic phases in a new homologous series of novel bent-core compounds

Abstract

Two new homologous series of isomeric achiral five-ring bent-core compounds containing 3,4-disubstituted biphenyl moiety have been synthesised and the mesophases that they exhibit characterised. Compounds of series A are obtained from 4-hydroxybiphenyl-3-carboxylic acid while those in series B are prepared by reversing the position of the hydroxyl and carboxylic groups. This change seems to have a profound effect on the mesophase properties. Interestingly, for compounds of series A containing the long terminal chain, a transition between two polar orthogonal smectic phases has been observed. The observed mesophases have been characterised using a combination of polarised light optical microscopy, differential scanning calorimetry, X-ray diffraction studies and electro-optical measurements. This is the first example of a transition between two partial bilayer polar orthogonal smectic phases. In addition, the effect of a fluoro substituent ortho to the strongly polar terminal cyano group on the mesophase has also been examined.

Key words:

• bent-core
• biphenyl moiety
• polar uniaxial smectic A
• polar biaxial smectic A

Acknowledgements

The authors wish to thank Mr R.N. Keshava Murthy for help in the synthesis and Ms K.N. Vasudha for technical support. We thank Mr Ram for making cells for conoscopy and the NMR Research Centre, Indian Institute of Science, Bangalore for recording the NMR spectra. BKS thanks the Indian National Science Academy, New Delhi, for financial support.