Optically biaxial interdigitated smectic A phase: liquid crystalline dimeric bidentate ligands and their metal complexes

Abstract

A detailed study into the synthesis and characterization of achiral nonsymmetric dimeric bidentate ligands formed by combining salicylaldimine and cyanobiphenyl rodlike anisometric segments through a flexible spacer (varying in its length and parity) and their Cu(II) and Pd(II) complexes is reported. The spacer parity greatly influences the phase behavior of ligands; notably, the dimers with odd-parity spacer stabilize nematic, uniaxial smectic A and biaxial smetic A phases, while the even-members display nematic and / or smectic phase/s. Unlike ligands, both the metal complexes solely show nematic behavior. An odd–even effect, as noted for ligands, was observed for the nematic–isotropic transition temperatures and the associated entropy values of copper complexes, while such behavior was not found in the case of palladium complexes.