Exploration of a 7.O4O.7 dimeric liquid crystal using temperature-dependent Raman spectroscopy and comparison with density functional theory.

Context: This article focuses on the temperature-dependent Raman spectroscopy analysis of a 7.O4O.7 dimeric liquid crystal, a single molecule. This dimeric compound consists of two symmetric monomers linked by a spacer. This compound exhibits two liquid crystalline phases: SmF and SmA. The article includes the shifting of peak position, variations in integral intensity, and changes in full width at half maximum (FWHM) with temperature fluctuations. The variations in Raman spectral characteristics with temperature provide evidence of charge displacement during phase transitions of the liquid crystal. The orientational and vibrational freedoms of molecules related to Raman bands in relation to temperature variation are also examined. Density functional theoretical approaches were employed to optimise the compound and to compare the Raman spectra at room temperature with experimental Raman data. The experimental and theoretical Raman results align exactly at room temperature, indicating that the basis set and functional employed in this investigation were valid for the 7.O4O.7 dimeric liquid crystal molecule analysed. The assignment of vibrational modes, observed in both experimental and DFT-generated data, was based on potential energy distribution (PED) utilising vibrational energy distribution analysis (VEDA) calculations.

Methods: All theoretical calculations conducted for the study utilised the Gaussian 09 software package. Gauss View 06 and VEDA 4 were employed for the analysis and visualisation of the compounds. The compound had been tuned for optimal performance using the B3LYP functional with the 6-31G (d,p) basis set. Experimental Raman spectroscopy was conducted using the Horiba Lab RAM HR Evolution Raman Spectrometer to obtain temperature-dependent Raman spectra.