Inducement of smectic phases in hydrogen-bonded mesogenic systems

Abstract

A new series of intermolecular hydrogen-bonded complexes has been synthesised using p-n-alkyl benzoic acids (nBA, where n = 5 to 10) and p-(p′-ethoxybenzylidene)-cyanoaniline (EBCA) moieties. The thermal and phase behaviour of the resulting compounds has been studied by polarising optical microscopy and differential scanning calorimetry. Thermal studies have also revealed the formation of the smectic G phase with a fine smooth multi-coloured mosaic texture. Moreover, the smectic A phase, with a focal conic fan texture, has also been observed, but only in the 10BA: EBCA compound. Detailed investigation of Fourier transform infrared and ¹H nuclear magnetic resonance (NMR) spectra suggests that stabilisation is the result of intermolecular hydrogen bonding between the acid group of nBA and the cyano group of EBCA. Powder X-ray diffraction has confirmed the orthorhombic arrangement of the molecules in the hydrogen-bonded complexes.

Keywords:

• induced Smectic G phase
• Smectic A phase
• hydrogen bonding
• alkyl benzoic acids

Acknowledgements

The authors are grateful for financial support from the Defence Research and Development Organisation (DRDO) through Project No ERIP/ER/0403448/M/01, dated 31-01-2005, New Delhi, and the Department of Science & Technology Fund for Improvement of Science & Technology Infrastructure (DST FIST), 2002, DST New Delhi, to the Department of Physics, Acharya Nagarjuna University.