Photoejection of electrons from pyrrole into an aqueous environment: ab initio results on pyrrole-water clusters

Ab initio (RHF, CASSCF and CASPT2) calculations in the ground and lowest excited singlet states have been performed on pyrrole and pyrrole–water clusters. Full geometry optimization in the 1πσ∗ state, which is energetically accessible from the optically allowed 1ππ∗ state, reveals the flow of the electronic charge from pyrrole towards the water molecules, i.e., the formation of a charge transfer-to-solvent state. The computational results indicate that pyrrole–water clusters are good models for the investigation of the mechanistic details of the electron solvation process occurring upon ultraviolet photoexcitation of organic chromophores in liquid water.