New variants of polymorphism in bananashaped mesogens with cyanosubstituted central core

Abstract

A new series of achiral five-ring banana-shaped compounds is presented which exhibit a cyano substituent in the 4-position of the central core. It follows from X-ray investigations and from NMR, microscopical and electro-optical measurements that all members of the series do not only form the chiral B2 phase characteristic of a bent molecular shape, but also SmA and SmC (in one case also nematic) phases. The electro-optical studies on the B2 phase prove an antiferroelectric ground state which can be switched into ferroelectric states. On the base of the experimental data plausible structure models have been proposed.