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 SmCPA and low-temperature crystalline BX 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 SmCPA 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.