Orientational transition of a bent-core dopant in an anticlinic liquid crystal matrix

Abstract

Small quantities of the bent-core mesogen P-7PIMB were dissolved in an anticlinic liquid crystal consisting of a mixture of left- and right-handed TFMHPOBC, with enantiomer excess X=0.2. For bent-core concentrations above C=3 wt %, differential scanning calorimetry shows the disappearance of the higher temperature synclinic phase, as well as the appearance of a new peak at a low temperature T _c. Polarized infrared absorption measurements indicate that the new DSC peak is due to an orientational transition of the bent-core molecules, analogous to the transition previously observed in a smectic A matrix. For T>T _c the plane of the bent-core molecules lies in the tilt plane of the anticlinic matrix, with the arrow (the symmetry axis) of the bent-core molecules parallel to the smectic layers. For T<T _c we deduce that the bent-core molecules lie within a single smectic layer, with the polar tilt of the arrow approximately equal to the polar tilt of the TFMHPOBC molecule and the vector connecting the two ends of the bent-core molecule perpendicular to the anticlinic tilt plane. Additionally, T _c was found to be an increasing function of bent-core concentration.