Time-resolved infrared spectroscopic study of molecular reorientation during ferroelectric liquid-crystal electro-optic switching

Polarized Fourier transform infrared (IR) absorption spectroscopy is used t o probe molecular conformation in a ferroelectric liquid crystal during the large-scale collective reorientation induced by an externally applied elec tric field. The absorption spectra of the planar-aligned cells of the ferro electric liquid crystals (FLC) W317 and 6OB(E)BB(3CN)O8* are measured as fu nctions of IR polarizer orientation and time following the reversal of the electric field applied to the FLC. The time evolution of the dichroism of t he absorbance profile due to the specific molecular vibration modes. partic ularly from the biphenyl core and alkyl tail, is observed. The reorientatio n rates of the core and the tail are found to be the same to within experim ental uncertainty. The dynamic experiments show that this rigid rod structu re is firmly maintained while the molecular axis rotates about the layer no rmal during field-induced switching.