Molecular arrangement in a chiral smectic liquid crystal cell studied by polarized infrared spectroscopy

The structure of the chiral smectic C phase (SmC^*) of the mesogen MHP10CBC in a homogeneously aligned thin cell, that exhibits V-shaped-like switching in a certain frequency range, was studied using polarized Fourier-transform infrared spectroscopy and optical microscopy. The molecular orientational distributions were analysed quantitatively in terms of dichroic parameters of the absorbance profiles, by taking into account the orientational properties of the transition moments for several phenyl and carbonyl bands. The polar angles of the transition moments, with respect to the molecular long axis and their azimuthal orientational parameters used in calculations, were determined from the infrared dichroic data for helical and electrically unwound structures in a thicker cell of this material. For a sufficiently thin cell in the SmC^* phase at zero electric field, the results on the azimuthal orientational distribution of the director over a ferroelectric liquid crystal cone, with respect to the substrate normal, are in agreement with the model of a partly twisted SmC^* structure. The voltage-dependent dichroic parameters in relation to the direction and the degree of the preferable orientation of the molecules in a sample are compared for the SmC^* and the SmC^*_A phases.