Unusual mesomorphic behaviour in bent-core compounds derived from 5-cyanoresorcinol

We describe the synthesis and mesomorphic properties of the first two homologous series of bent-core compounds derived from 5-cyanoresorcinol. The lower homologues in both series show a normal B 1 phase, and the mesophase of higher homologues exhibits very unusual textures and electro-optical switching behaviour. The observation of spiral growth patterns under a polarizing microscope, and only layer reflections from X-ray diffraction studies for these homologues, suggests that this mesophase is different from a B 2 phase. This mesophase shows chiral domains of opposite handedness which can be identified from electric field experiments. Under a triangular-wave electric field, at lower voltages although the mesophase shows a ferroelectric type switching behaviour it is actually antiferroelectric in nature. The observation of helical structures and spontaneously formed chiral domains suggests that the mesophase is a variant of the B 2 phase.