A temperature-dependent Raman study of 5CB, fully deuterated 5CB, and aromatically deuterated 5CB combining experimental and theoretical approaches

This article exhibits a comprehensive examination and investigation of temperature-dependent Raman spectra, including theoretical Raman spectra derived from quantum mechanical density functional theory. The compounds used in this investigation comprised pure 4'-pentyl-4-biphenylcarbonitrile (5CB) liquid crystal, encompassing its fully deuterated form (5CB full D) and its aromatic deuterated variant (5CB aromatic D). The research is significantly influenced by temperature, examining the effects of deuterated systems on intricate phase transitions, molecular reorientations, and the vibrational properties of molecules within the 800-2500 cm^-1 spectral range. This study analyses the variations in Raman spectral characteristics, including peak position, integral intensity, linewidth, area, and height, during transitions among the crystal, isotropic, and nematic phases. Raman spectral data for pure 5CB, 5CB full D, and 5CB aromatic D were collected across temperatures spanning the isotropic and nematic phases. The results reveal significant alterations and fluctuations in the intensity of several vibrational peaks, providing insights into molecular interactions, order parameters, and the effects of deuteration on the structural dynamics of pure 5CB liquid crystal. The outcomes indicate that alterations in hydrogen and deuterium significantly affect molecular vibrations, particularly in the aromatic and alkyl regions, and elucidate the consequences of these changes on phase transition processes.