Vibrational dynamics in liquids and frozen matrices. Concentration and solvent effects in phenylacetylene by low temperature Raman spectroscopy Original Research Article

Raman spectra of the νs(CC) stretching mode of phenylacetylene (PA) dissolved in different solvents: methylcyclohexane, acetonitrile and benzene in frozen matrices at 77 K as a function of concentration have been recorded and compared with the spectra in the liquid phase. The optical measurements were complemented by the differential scanning calorimetry (DSC) scans. The results reveal some dramatic changes with solvent and concentration and are of potential relevance both to fundamental condensed phase modelling and to liquid crystal technology. We have discussed the origin of the splitting observed for the νs(CC) stretching mode of phenylacetylene (PA) and we have found that H-bond interactions are responsible for the observed substructure in the vibrational spectra. We have found a glass-like transition at 183 K and two melting-like transitions at 200 and 218 K for PA in acetonitrile. In methylcyclohexane a melting transition starts at 120 K, and does not change in PA solution in contrast to PA in acetonitrile. The DSC scan for PA in methylcyclohexane shows additional phase transition at about 220 K.