Dynamics and mechanism of the Crystal II → smecticG phase transition in TB7A by a temperature‐dependent micro‐Raman study and DFT calculations

Abstract

The solid to smecticG (SmG) phase transition in a Schiff base liquid crystalline compound, terepthal-bis-heptylaniline (TB7A), is monitored in situ by temperature-dependent Raman microspectroscopy, using the band of a C-H in-plane bending mode as a marker. Contrary to the earlier report of a sudden wavenumber shift, the in situ measurement shows very clearly that a new Raman band at ∼1160 cm −1 appears at the Crystal II → SmG transition. The dynamics of this phase transition is discussed in terms of a triple well potential below 210 K and a double well potential above 210 K. The phase transition essentially takes place as a result of intra-molecular rotation about the long molecular axis. The optimization energy at various fixed dihedral angles, (-C-C-C N-) are calculated using density functional theory (DFT) at the B3LYP/6-31G * level of theory. The relative energy at each dihedral angle is calculated relative to optimization energy obtained without any constraints and plotted as a function of dihedral angle ( ) between the adjacent phenyl ring planes, which also shows a double well potential at room temperature.

Study of phase transitions in a bent-core liquid crystal probed by infrared spectroscopy

“…The very strong peak in this region at 1204 cm À1 is associated with coupled mode of ring C6-O55 stretching along with phenyl ring CC stretching, CH in-planebending and trigonal deformation of the ring. This region also showed the spectral changes during all the three phase transitions due to the change in relative orientation of four phenyl rings facilitating the intramolecular charge transfer [4].…”

“…The combination of vibrational spectroscopy and quantum chemical approach has been widely used to understand the mechanism of phase transitions in liquid crystals at molecular level [3][4][5]. The crystal !…”

A combined experimental and theoretical approach to study SmC → NcybC phase transition in a four-ring bent-core liquid crystal

“…be a sensitive indicator of the phase transition [16][17][18] in liquid crystals. be a sensitive indicator of the phase transition [16][17][18] in liquid crystals.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part IV

“…Phase transitions were described by Vikram et al [242] involving the dynamics and mechanism of the crystal II smectic G phase transition for erepthal-bis-heptylaniline by a temperature-dependent micro-Raman study and DFT calculations. Yang et al [243] investigated the mechanism of solid-state polymorphic transition of p-aminobenzoic acid (PABA) using in situ Raman spectroscopy.…”