Polarized FTIR spectroscopic study of a high-temperature ferrielectric phase of an antiferroelectric liquid crystal

The molecular orientational distribution for a homogeneously aligned cell of an antiferroelectric liquid crystal (R)-(-)- 1-methylheptyl-4-(4'-dodecyloxybiphenyl-4-ylcarbonyloxy)-3-fluorobenzoate (with acronym (R)-120BP1M7) in the high-temperature ferrielectric (FiLC) phase is studied using FTIR spectroscopy. For several characteristic bands, the polarization dependence of the absorbance is analyzed for different stages of the electrically induced transformations of the sample structure, including the phase transition from the RLC phase to the Sm-C* phase and the helix unwinding. A qualitative similarity of the voltage dependence of the angular shift of the absorbance profile for the "chiral" carbonyl band to that of the macroscopic polarization is found. The presence of rotational orientational biasing of C=O groups around the long molecular axis is confirmed by the IR dichroic data for the field induced Sm-C* phase.