Polar smectogens: polymorphism of some cyanoalkoxybiphenylalkoxybenzoates and related compounds

A series of new cyanoalkoxybiphenylalkoxybenzoates containing a highly dipolar end group electrically and mechanically decoupled from the rigid moiety has been synthesized. The thermal behaviour of these compounds and their precursors (cyanoalkoxyhydroxybiphenyls) has been investigated by means of differential scanning calorimetry and optical polarizing microscopy. It has been found that such compounds often exhibit double melting behaviour through isotropic or smectic phases. A rather rich polymorphism (N, S_A, S_B and S_E phases) is observed at high temperature (100-200°C).