Dynamics of electric-field-induced molecular reorientation of a surface-stabilized antiferroelectric liquid crystal in the smectic-C* phase probed by time-resolved infrared spectroscopy.

Polarization dependent and time-resolved Fourier transform infrared studies have been carried out on the electric-field-induced ferroelectric phase (Sm-C*) of a chiral, antiferroelectric liquid crystal at different temperatures. Polarization dependent infrared spectra under dc electric field reveal that the average alkyl chain axis does not coincide with the mesogen axis and is less tilted with respect to the layer normal than the mesogen. The analysis of the various absorbance profiles obtained from temporal response of absorption changes of infrared bands at different time delays provides clear evidence for biased orientation and hindered rotation of almost all the molecular segments around the average molecular long axis and the rotation of the whole molecule around its axis is also hindered. It is further inferred that the mesogen, the chiral segment, and the alkyl chains reach their equilibrium orientations at nearly the same time on switching the polarity of the ac electric field but the different molecular segments reorient through different angles.