Polarized Infrared Spectroscopic Study on Hindered Rotation around the Molecular Axis in the Smectic-<i>C</i>* Phase of a Ferroelectric Liquid Crystal with a Naphthalene Ring. Application of Two-Dimensional Correlation Spectroscopy to Polarization Angle-Dependent Spectral Variations

Abstract

Polarization angle-dependent infrared spectra of a ferroelectric liquid crystal with a naphthalene ring in the smectic-C* phase were measured at 60 °C under dc voltage of 40 V with positive and negative polarity for investigating the relative orientation of the alkyl chain, mesogen, and chiral segments. The obtained polarization angle-dependent infrared spectra were analyzed by two-dimensional (2D) correlation spectroscopy. The 2D correlation analysis clearly detects slight phase differences in the polarization angle dependence which are hardly recognized by ordinary plots of intensity changes in infrared bands. It has been revealed from the 2D correlation analysis that not only the two carbonyl groups, but also other parts of molecule, carry out hindered rotations about the long molecular axis. The 2D correlation analysis also allows us to separate a CH3 asymmetric stretching band due to the chiral methyl group from those arising from other methyl groups. The CO stretching bands due to the carbonyl group in the chiral part are also separated by 2D correlation spectroscopy into two bands, which may arise from the rotational isomerism around the O−C axis of the chiral part.