Different nematic phases and a switchable SmCP phase formed by homologues of a new class of asymmetric bent-core mesogens

Abstract

Ten homologues of a new class of asymmetric bent-shaped compounds have been synthesized. Their mesophase behaviour was investigated by polarizing microscopy, X-ray diffraction, dielectric and electro-optical measurements. The long-chain members of the series C₈–C₁₆ exhibit the switchable antiferroelectric SmCP phase. The short-chain members C₄–C₈ form a nematic phase. The homologues C₅ and C₆ show a transition from the nematic into a low-temperature phase which is indicated by a sharp peak in the DSC trace. Whereas the textures point to a nematic–smectic transition, the X-ray studies definitely prove a structure without any long range (or quasi long range) positional order in the low-temperature phase. A molecular model is described which exhibits structural features similar to those of a N_Col phase, which can be regarded as the precursor of the following columnar phase (B₁ phase).