Dynamics of FLCs with a tilted bookshelf structure using time-resolved FTIR spectroscopy

Time-resolved FTIR spectroscopy with microsecond resolution was applied to the switching process of FLCs using an IR polarizer attached to a microscope whose axis was set along the aligning direction (direction of SiO flux). A tilted bookshelf geometry with a layer tilt angle of approximately 34° was obtained by alignment using obliquely evaporated SiO layers in a CaF₂ cell with about 1.7 μm gap. Six kinds of FLC mixtures were prepared by mixing 5 wt % of a chiral molecule with host mixtures of phenylpyrimidines. By monitoring an absorption band at 1432 cm^-1, assigned to vibrational modes of the pyrimidine skeleton, it was found that the molecular long axis either rotates along the upper side or along the lower side of the cone during switching. Moreover, we investigated the relationship between the rotational direction of the directors and the stability of the dark level transmission during multiplexing. The dark level transmission during rotation along the upper side of the cone may fluctuate less than that during rotation along the lower side of the cone. We found that the bias stability of the dark level transmission is closely related to the direction of the rotation along the cone. The direction of the rotation of FLCs along the cone was therefore found to play an important role in realizing high contrast ratios during multiplexing.