Ultrashort orientational dynamics of liquid crystals in the smectic-A phase

A femtosecond time-resolved optical Kerr effect experiment was carried out to study the reorientational motion of a series of cyanobiphenyl molecules around their long axis in the smectic-A phase. The Kerr effect was found to mainly result from the reorientation of the cyanobiphenyl core of the liquid crystal molecule. Three relaxation times were observed in the subpicosecond and picosecond range. They appear to be associated with libration and diffusive reorientations of chromorphores of individual and paired molecules. The analysis on several temporal scales reveals the existence of strong molecular interactions within the smectic-A layers.