Molecular Structure of a Partly Deuterated Chiral Smectic Liquid Crystal Studied by Polarized FTIR Spectroscopy

Abstract

The molecular structure of a partly deuterated chiral smectic liquid crystal 4- in a homogeneously aligned sample is studied using polarized Fourier-transform infrared (FTIR) spectroscopy. The relative orientations of the chiral and deuterated achiral alkyl chains of molecules with respect to their long axes and some properties of the orientational distributions of the carbonyl groups are quantitatively analysed for the ferroelectric SmC * phase with a field unwound structure. The analysis is carried out in terms of the absorption anisotropy of several bands related to stretching vibrations of the phenyl C 6 H 4 fragment, the deuterated biphenyl C 12 D 8 fragment, two carbonyl groups situated in different parts of a molecule, the methylene groups CH 2 and CD 2 . It has been found that the chiral and achiral alkyl chains make substantially different angles (∼60 • and ∼36 • , respectively) with the molecular long axis. The rotational orientational distribution of the carbonyl groups about the molecular long axes has been found to have a comparatively low polar biasing.Keywords Infrared spectra of a deuterated FLC compound; biasing in a FLC compound; IR dichroism; mobility of chains in a FLC compound

Temperature-Dependent Infrared Spectroscopy Studies of a Novel Antiferroelectric Liquid-Crystalline Thiobenzoate

“…Most efforts were made to understand the recorded spectral data since most of the mesogens exhibit an extremely complex vibrational dynamics due to a large molecular size described by a low symmetry. − In the 1980s Fontana et al also proved the vibrational spectroscopy to be a valuable tool in the molecular dynamics studies of some simpler nematic systems. , The molecular reorientation studies in the far-infrared range were also reported by Janik’s team. , However, the rebirth of vibrational spectroscopy in the discussed field was observed in the 1990s, mainly along with the progression of the ferroelectric smectics studies. Since the early works by Kocot et al dealing with order parameters and molecular tilt angle, − many papers presenting successful application of infrared spectroscopy were reported. − In parallel, significant papers by Kim et al − have confirmed the applicability of Raman spectroscopy in related studies and opened the discussion for antiferroelectric liquid crystals. Most experiments have been performed for planar sample configuration; however, in the early 2000s, the alternative way of studying the most important order parameters and the molecular tilt angle was proposed. , Finally, vibrational spectroscopy has become a relevant tool in the studies of de Vries type or biaxial nematic phases. − As modern quantum chemistry allows us to predict the vibrational spectra with very good accuracy, the experimental data may be nowadays deeply understood and interpreted, giving even further information about the components of the related transition moments, despite the high complexity of the recorded data. − …”