Crystal—Smectic G Transformation Investigated by Temperature-Dependent Raman Study

Abstract

We report on a temperature-dependent Raman study of terephthalidine-bis-butylaniline (TBBA) and terephthalidine-bis-heptylaniline (TB7A) in the temperature range 10–406 K and in the wavenumber regions 1120–1240 cm⁻¹ and 1500–1700 cm⁻¹. The variations of peak positions and linewidths of several Raman marker bands with temperature, which clearly show crystal–SmG transition at ∼334 K, have been used to discuss the dynamics of this phase transition. The temperature-dependent Raman study revealed that the increased vibration of the long alkyl tail and the rotation around the long molecular axis are the two primary phenomena responsible for the crystal–SmG transition. Density functional theory (DFT) at the B3LPY/6-31G(d) level was employed to obtain the optimized geometry and the harmonic vibrational wavenumbers of TBBA. The eigenvectors of the modes corresponding to these marker bands were also calculated.