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.