New mesogenic compounds exhibiting a thermotropic optically isotropic phase

The only two series of carboxylic acids, 3-nitro- or 3-cyano-4-alkoxybiphenyl-4-carboxylic acid, are known to exhibit the optically isotropic phase (SID). Now we synthesised 4-(branched alkoxy)-anilinebenzylidene-4'-carboxylic acid series, all being racemic, and investigated their mesophase properties by means of DSC, optical microscopy and X-ray measurement. A, a result, some branched azomethine derivatives were found to form a SD phase. We also synthesised cinnamic acid derivatives with branched alkoxy tail that were turned out to exhibit either SD phase or hexagonal columnar phase. We tried biphenyl or azobenzene core analogues which were found to produce a highly ordered smectic phase or no mesophase, respectively. At this stage, we suppose it plays an important role that the branch is introduced into the terminal chain and a certain dipole moment is located within the mesogenic core. These factors may allow the peculiar molecular packing that causes an optically isotropic property.