At the boundary to banana-shaped liquid crystals: polar properties of phases formed by new asymmetric achiral four-ring bent-core mesogens

New asymmetric four-ring bent-core compounds derived from N-benzoylpiperazine are presented. The mesophases were characterized by polarizing microscopy, DSC, X-ray diffraction, dielectric, electro-optical and SHG measurements. In some homologues the SmA as well as SmC phase can be transformed into a polar structure by applying an electric field. It was found for the first time that the polar SmI phase shows a ferroelectric switching which is obviously based on the collective rotation of the bent molecules around their long axes. It is remarkable that the ferroelectric structure is preserved on cooling into the solid state.