A comparative laser Raman study on TB4A, TB7A and TB10A

Abstract

The basic structural di erences between three thermotropic liquid crystals TB4A, TB7A and TB10A have been interpreted by analysing their Raman spectra. Three spectral regions, 925± 1025, 1275± 1475 and 1525± 1650 cmÕ 1 , have been chosen in this context to incorporate their structural dissimilarity. The induced planarity of the backbone, as an e ect of increasing chain length, has been studied by observing the changes in the respective Raman spectra of the three compounds. A tentative assignment of all the modes observed in the region 400± 1700 cmÕ 1 is made in this context. The molecular conformations of the three compounds have been predicted in their solution states, and are compared with the molecular environment that exists in their liquid crystalline states. Structural disorder at the solid± SmG transition is discussed and the changes are incorporated systematically.

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

“…The temperature-dependent Raman spectra of two liquid crystalline systems TBBA and TB7A belonging to the same series as TBDA, which undergo Crystal ® CrystalG transitions 11 at 334.8 and 385.5 K, respectively, were recorded. Raman spectra were obtained using a Spex 1404 double monochromator equipped with a 2400 lines/mm grating and a charge-coupled device (CCD) detector.…”

“…A good amount of work has been done [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] to study the phase transitions in liquid cr ystals through linear and nonlinear Raman spectroscopy. The importance of the Raman spectroscopic method is that it is a m icroscopic technique whereby a trace of molecular rearrangement in different m esophases can be established, whereas the most widely used traditional techniques 13 to investigate and characterize liquid crystalline phases, viz.…”

“…14 The members of terephthalidine-bis-alkylaniline (TBAA) homologous series demonstrate a very clear Crystal-SmG transition in Raman measurements. 1,2,6,11,12 Two m embers of this series, namely TBBA and TB7A, have been selected for the present study. The Cr ystalG phase, also known as the sm ecticG (Sm G) phase, is an improper liquid crystalline phase with almost no liquidity, where three-dimensional positional ordering remains, but there is considerable disorder in molecular orientation.…”

Study of a high-temperature Raman-sensitive mode of TBDA at the solid-smectic G transition

“…2. In the two earlier Raman studies, 10,11 this mixed order nature of the solid-SmG transition was not explicitly exhibited. 10 Considering the band at ca 975 cm 1 , the solid-SmG transition is confirmed both by splitting of the band and the linewidth vs temperature plot.…”

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

“…[13] In this study the temperature-dependent Raman spectra of TB7A, which undergoes a Crystal II → SmG transition at 334.8 K, [14] were recorded on a Spex 1404 double monochromator equipped with two 2400 lines/mm gratings, a liquid N 2 cooled charge-coupled device (CCD) detector (Photometrics) and a microscope. The radiation of the 647 nm line from a krypton ion laser with a power of 5 mW at the sample was used.…”