Mesomorphism of a banana mesogen: influence of a fluoro substituent in the central core

Abstract

The results of experiments with stable five-ring banana-shaped molecules consisting of laterally 4-fluoro substituted 1,3-phenylene ring as the central unit in Bis-[4-(4′-n-alkyloxybenzoyloxy)salicylidene]-phenylene-4-fluoro-1,3-diamines are presented. These compounds are thermally and hydrolytically stable due to intermolecular or intramolecular hydrogen bonding and exhibit SmCP_A and low-temperature crystalline B_X phases. The phases had been characterised by thermal microscopy and differential scanning calorimetry. A representative example has also been characterised by X-ray diffraction studies and electric field effects. The influence of a lateral fluoro substituent in the central core is clearly demonstrated with the induction of the SmCP_A phase which is absent in the parent compound without the substituent. Further these compounds exhibit a large tilt angle. We also describe a comparison of phase behaviour with similar analogous compounds, taking the position of fluoro substitution, changes in the linking groups and the direction of the linking groups into consideration.

Keywords:

• Banana shaped mesogens
• Fluoro compounds
• SmCP_A phases
• Spontaneous polarization

Acknowledgements

Financial support was provided by DST, DAE and DRDO. We are grateful to Professor K. A. Suresh, Professor N. A. Clark and Dr C. Jones for their help in providing some experimental facility.