Influence of molecular structure on phase transitions in liquid crystal binary mixtures: The role of the orientation of the central ester

Two series of liquid crystals containing a tolane-core surrounded by an ester and a sulfinic ester, with different paraffinic side chains, were synthesized and characterized. The rigid core includes an internal ester and a terminal sulfinic ester. The two series differ in the orientation of the internal ester, being either parallel or antiparallel to the sulfinic ester. It is shown that the orientation of the central ester, which modulates dipole-dipole interactions, and the length of the flexible side chains greatly influence their mesogenic properties. Binary mixtures of the two series have been prepared and phase diagrams are reported. The results provide insight into the role of these structural features which extend the thermal stability of the smectic C phase. Behavior of these series is compared to previous results on homolog series containing two esters, in order to better understand the role of the central ester orientation on the liquid crystal polymorphism.