Experimental (FT-IR, FT-RS) and theoretical (DFT) studies of vibrational dynamics and molecular structure of 4-n-pentylphenyl-4′-n-octyloxythiobenzoate (8OS5)

Fourier transform Raman (FT-RS) and infrared (FT-IR) spectra were recorded for the 8OS5 samples in the solid state. The equilibrium geometries, harmonic vibrational frequencies, infrared and the Raman scattering intensities were computed using the Gaussian 03 package. Computations were made using density functional theory (DFT) with the following functionals: B3LYP, B3PW91, PBEPBE, mPW1PW91 and SVWN at the 6-31+G(d) basis set level. Calculations for B3LYP functional, chosen as giving the most reliable results in this case, were followed with the 6-311+G(d,p) basis set. Results obtained at this level of theory were used for a detailed interpretation of the infrared and Raman spectra, based on the potential energy distribution (PED) of the normal modes. The good agreement between the observed and calculated frequencies is shown. Liquid crystalline polymorphism of 8OS5 was explored by FT-MIR measurements as a function of temperature. Noticeable spectral changes with temperature indicating the phase transitions are reported.