Density functional theory and two-dimensional correlation polarized infrared spectroscopy studies on the anti-ferroelectric liquid crystal (1-methylheptyl)4-(4′-decyloxy-4-biphenyl) oxymethylene benzoate

The structure and vibrational frequencies of the chiral anti-ferroelectric liquid crystal molecule (AFLC) (1-methylheptyl)4-(4′-decyloxy-4-biphenyl) oxymethylene benzoate (MHDBOB) have been investigated by using the density functional theory (DFT) with the B3LYP/6-31G(d,p) level. The observed vibrational spectra have been resolved and assigned in detail by comparison to the computed values. The results indicate that the computed and observed spectra are in good agreement with each other. The molecular stable structure obtained by using DFT theory, shows that the two hydrocarbon chains are all-trans zigzag conformer and nearly perpendicular to each other. The orientation of the mesogen part and the hydrocarbon chains for MHDBOB at 109 °C was investigated by employing the polarization-angle-dependent infrared spectra in the electric field induced and the two-dimensional (2D) correlation spectroscopy. To combine the experimental with theoretical results, it can be concluded that the azimuth of the achiral and chiral chain is opposite to each other, the orientation of the achiral chain is in the same direction as the mesogen core and that of the chiral chain is perpendicular to the mesogen part. Their axes are parallel and perpendicular to the average molecular long axis, respectively. Two CH2 chains (achiral and chiral) are both a probable all-trans zigzag conformer. These results are quite new and different from the previous results, which show that the hydrocarbon chains of AFLC and/or ferroelectric liquid crystals (FLC) are in disorder.