Liquid crystalline transition or liquid–solid interface vibrational dynamics of diphenylacetylene in solutions by Raman spectroscopy? Original Research Article

Raman spectra of the stretching mode νS(CC) (Ag) at 2224 cm−1, the C–Ph bending in plane mode (B3g) at 535 cm−1, the low frequency Raman region from 15–200 cm−1 of diphenylacetylene (DPA) in methylcyclohexane and acetonitrile as well as the rocking mode of methylcyclohexane (A′) at 547 cm−1 in isotropic liquids, liquid ordered phases, and solid matrices as a function of temperature have been recorded in the range 293–77 K. We have found that DPA–methylcyclohexane system exhibits isotropic liquid–anisotropically aligned liquid phase transition at 258 K and liquid–solid transition at 150 K. Mechanisms of vibrational relaxation and band broadening around 258 and 150 K transitions have been discussed. We have found that DPA molecules modify significantly reorientation order of the host solvent molecules in the phase below 258 K that strongly deviates from isotropic alignment observed in the liquid phase above 258 K. This anisotropic alignment may come from liquid crystalline properties of DPA or liquid–solid interface interactions between methylcyclohexane molecules adsorbed on surfaces of DPA crystals.