Orientational and Vibrational Relaxation Dynamics of Perylene in the Cyclohexane-Ethanol Binary Solvent System

The rotational dynamics and vibrational population relaxation of the nonpolar probe molecule perylene have been studied in a series of ethanol-cyclohexane binary solvent mixtures, with the goal of relating solvent system composition to local organization. Steady-state spectroscopic data show that there is a discontinuous dependence of the spectroscopic origin on binary solvent system composition for perylene. Both rotational diffusion and vibrational population relaxation time constants show a clear discontinuity between 5% and 7.5% (v/v) ethanol in cyclohexane, suggesting a discontinuous change on molecular scale rearrangement in the chromophore local environment. We interpret these results in the context of the chromophore residing in an environment that is not homogeneous on the molecular scale and changes in its average conformation with binary solvent system composition.