Vibrational spectroscopy of structure transformation in two isomers of mezogenic 4-alcoxyphenyl-4′-alcoxybenzoates

For substances 4-(n-hexyloxy)phenyl-4′-(n-octyloxy)benzoate and 4-(n-octyloxy)phenyl-4′-(n-hexyloxy)benzoate forming liquid–crystalline mesophases the Raman spectra in the region of 1000–3000 cm−1 were measured and assigned. The information on molecular geometry was obtained by quantum-chemical simulation. The calculations were made using the Gaussian-03 package at the HF/3-21G level of theory. Separately we investigated the temperature dependence of Raman spectra for the vibrational bands in the spectral range 1100–1350 and 1550–1750 cm−1 during the cooling process. The cooling rate was 1–2 K/min, and quasi-static condition of appropriate temperature processes was achieved in such a way. Noticeable changes in Raman spectra with temperature changing indicating the phase transitions are reported.