Theoretical Investigation of Excited State Proton Transfer Process in the N-Salicylidene-2-bromoethylamine

Excited state reaction coordinate and the consequent energy profiles of a new Schiff base, N-salicylidene-2-bromoethylamine, have been investigated at the CC2 level of theory. The electron-driven proton transfer and torsional deformation have been identified as the most important photochemical reaction coordinates. In contrast to the ground state, the excited state potential energy profile shows a barrierless dissociation pattern along the O-H stretching coordinate, which verifies the proton transfer reaction along the O-H coordinate at the S(1) state. The calculations showed that the PT is electron driven and that the S(1) transition has charge transfer character. The keto-type S(1) state attained by barrierless proton transfer is found to be unstable via a torsional motion, which provides fast access to a S(1)-S(0) conical intersection. From the conical intersection, a barrierless reaction path directs the system back to the enol-type minimum of the S(0) potential energy surface, thus closing the photocycle.