Bent-core mesogens with biphenyl moieties:: observation of a B7 to B4 phase transition

Four new bent-core mesogens containing biphenyl moieties are reported. All these, except the first homologue, exhibit B-7 and B-4 banana phases, both of which are known to have a helical structure. The B-7 to B-4 phase transition is very rare, this being perhaps only the second report of the observation of such a phase sequence. The first homologue exhibits only one mesophase X-1 with textural features reminiscent of the B-1 phase. All the compounds synthesized are characterized by spectral data. The mesophases exhibited by these compounds are characterized by polarizing optical microscopy, differential scanning calorimetry and X-ray studies.