Excited-state proton transfer in 7-hydroxy-4-methylcoumarin along a hydrogen-bonded water wire

The TDDFT, RI-CC2 and CIS calculations are performed for the nondissociative excited-state proton transfer (ESPT) in the [S.sub.1] state of 7-hydroxy-4-methylcoumarin (7H4MC) along a H-bonded water wire of three water molecules bridging the proton donor (OH) and the proton acceptor (C=O) groups. The TDDFT and RI-CC2 methods appear to be reliable approaches to describe the energy surfaces of ESPT.