Solvent induced charge separation in the excited states of symmetrical ethylene: A direct reaction field study

The polarization of the excited states of near-perpendicularly twisted ethylene in the condensed phase has been investigated by means of direct reaction field (DRF) calculations. In these calculations, five organic solvents with variable polarity and polarizability were simulated by 50 discrete, classically described solvent molecules. The excited states of near-perpendicular ethylene were described by ab initio methods at the CISD level of theory using a DZV basis set. It is demonstrated that there is a distinct correlation between the polarity of the solvent and the occurrence and stabilization of charge separated excited states of ethylene. Large dipole moments were observed for ethylene excited states in polar solvents, indicating that an asymmetric distribution of polar solvent molecules around the ethylene can introduce enough symmetry breaking to cause charge separation. This behavior was not observed for (models of) nonpolar solvents. This charge separation process can be designated as unbiased "sudden polarization" since the solvent shells used were in equilibrium with the nonpolarized ethylene solute.