Effect of Molecular Structure on Mesomorphic Behavior. 17.¹Cyano Terminated Twin Liquid Crystals

Abstract

Three homologous series of cyano terminated liquid crystalline Siamese Twins (imines, esters and biphenyls) having a rigid-flexible-rigid molecular structure have been synthesized and studied. All three series exhibit a strong odd: even alternation in N-I temperatures with the differences in chemical linkage between aromatic rings being of secondary importance. For one series (the biphenyls) transition enthalpies and entropies were obtained. The N-I transition is accompanied by a strong and regular odd: even alternation of both ΔH and ΔS values as the flexible segment is increased.