Structures and dynamics of phenol clusters in benzene solutions

Structures and dynamics of phenol clusters ((PhOH)n, n = 1-3) in benzene (Benz) solutions ([(PhOH)n]Benz) at 298 K were studied using intermolecular potentials derived from the Test-particle model (T-model) and molecular dynamics (MD) simulations. Although Benz molecules interact weakly among themselves and with PhOH, the average three-dimensional structures and interaction energy distributions obtained from MD simulations showed that, they could form well-defined solvent cages in [(PhOH)n]Benz. At infinite dilution, some solvent-separated structures, in which a Benz molecule linked between two PhOH molecules, were observed in [(PhOH)2]Benz, whereas hydrogen bond (H-bond) structures dominated in [(PhOH)3]Benz. Based on the observation that, under thermal equilibrium conditions and at short time, the exchange dynamics between the associated and dissociated forms involved periodic motions of the O-H⋯π H-bond, the lifetimes of the PhOH-Benz 1:1 complex were estimated and in reasonable agreement with 2D-IR vibrational echo experiment. Due to high potential energy barriers on the average potential energy landscapes, solvent exchanges in [(PhOH)n]Benz could take place through large-amplitude intermolecular vibrations of molecules in the first solvation shell. In order to provide insights into structures and dynamics in [(PhOH)n]Benz, it was shown that, explicit solvent molecules have to be included in the theoretical models.