Conical intersections in solution: non-equilibrium versus equilibrium solvation

In this contribution we discuss some dynamical properties of a recently proposed protonated Schiff base model to study the solvation effect on conical intersection (CI) dynamics [I. Burghardt, L. S. Cederbaum, and J. T. Hynes, Faraday Discuss. 127, 395 (2004)]. We consider two dynamical solvation regimes: equilibrium and non-equilibrium. In the first regime, the solvent instantaneously equilibrates to the evolving solute charge distribution, an assumption of many schemes for quantum chemical calculations in solution. In the second regime, appropriate for describing the actual dynamics, account is taken of the (inertial) dynamics of the solvent electrical polarization field. In this regime, both the excited electronic state dynamics and the non-adiabatic transitions in the CI region leading from the excited state to the ground electronic state, calculated via a surface hopping method, are found to differ significantly from those which follow from an equilibrium solvation characterization. Nonetheless, an equilibrium solvation description is useful in locating the seam of CIs which results from the chromophore–solvent interaction.