Photoinduced charge separation in indole–water clusters

Ab initio (RHF, MP2, CASSCF and CASPT2) calculations in the ground and the lowest excited singlet states have been performed for indole–water clusters. The calculations reveal a remarkable role of the lowest 1πσ∗ state in the photochemistry of these systems: indole in the 1πσ∗ state ejects an electron into the aqueous environment, leading to the formation of a charge-separated state. The computational results indicate that indole–water clusters are good models for the investigation of the mechanistic details of the electron solvation process occurring upon UV photoexcitation of indole and tryptophan in liquid water.