Field-induced inversion of chirality in SmCP A phases of new achiral bent-core mesogens

A new series of achiral bent-core mesogens is presented. The mesophase behaviour has been investigated using differential scanning calorimetry, polarizing microscopy, X-ray diffraction, and dielectric and electro-optical measurements. Depending on the length of the terminal chains the homologues form nematic phases, conventional smectic phases (SmA, SmC) and polar smectic phases (SmCPA). It was found that the switching mechanism of the SmCPA phase depends on the temperature. At lower temperature the switching takes place in the usual way by rotation of the director around the tilt cone. At higher temperatures the switching is based on a collective rotation around the long axes which corresponds to a field-induced inversion of the layer chirality. Surprisingly the SmC phase also shows an unusual electro-optical response.