Monte Carlo Quantum Mechanical-Configuration Interaction and Molecular Mechanics Simulation of Solvent Effects on the n → π∗ Blue Shift of Acetone

A Monte Carlo simulation method, making use of a combined quantum mechanical-configuration interaction and molecular mechanics (QM-CI/MM) potential, is described to examine the solvatochromic blue shifts of the n → π∗ transition of acetone in aqueous and organic solvents. The calculation correctly predicts the spectral blue shifts of acetone in polar solvents, while the experimentally-observed dispersion red shift in nonpolar solvents was not reproduced. The discrepancy is attributed to the use of nonpolarizable potential functions for the solvent, which exclude explicit solute-solvent dispersion interactions. Nevertheless, the results reported in this paper demonstrate the viability of simulation studies of solvent effects on electronic excitation. The method provides the opportunity to investigate photochemical processes and reactions in solution.