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

✍ Scribed by K. Vikram; Sunil K. Srivastava; Animesh K. Ojha; S. Schlücker; W. Kiefer; Ranjan K. Singh

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 271 KB
• Volume: 40
• Category: Article
• ISSN: 0377-0486
• DOI: 10.1002/jrs.2188

✦ Synopsis

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 (Φ) between the adjacent phenyl ring planes, which also shows a double well potential at room temperature. Copyright © 2009 John Wiley & Sons, Ltd.