New variants of polymorphism in banana-shaped mesogens with cyano-substituted central core

A new series of achiral five-ring banana-shaped compounds is presented whic h exhibit a cyano substituent in the 4-position of the central core. It fol lows from X-ray investigations and from NMR, microscopical and electro-opti cal measurements that all members of the series do not only form the chiral B-2 phase characteristic of a bent molecular shape, but also SmA and SmC ( in one case also nematic) phases. The electro-optical studies on the B-2 ph ase prove an antiferroelectric ground state which can be switched into ferr oelectric states. On the base of the experimental data plausible structure models have been proposed.