Probing field-induced submolecular motions in a ferroelectric liquid crystal mixture with time-resolved two-dimensional infrared spectroscopy

Time-resolved two-dimensional infrared (2D IR) spectroscopy has been applied to analyse an electro-optic switching ferroelectric liquid crystal (FLC) mixture. The 2D IR correlation technique clearly shows that the Goldstone mode in the SmC* phase is suppressed by an applied electric field. The field-induced reorientation process initiates from intramolecular motions in about 10 mu s. The intramolecular motions then propagate from the molecular segments attached to the same molecule to those fragments on other surrounding molecules. During the field-induced switching, the IR dipoles undergo a collective reorientation but with hindered rotation about the molecular long axis.