Excited State Proton Transfer Process In The 2-hydroxy –N-Salicylidene Schiff Base

The Excited state reaction coordinates and the consequent energy profiles of a new Schiff Base N- Salicylidene-2-Bromoethylamine (NSBA) 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. The potential energy profiles of the ground and the lowest excited singlet state are calculated. In contrast to the ground state, the excited state potential energy profile shows a barrier-less dissociation pattern along the O–H stretching coordinate which verifies the proton transfer reaction at the S1 (ππ*) state. The calculations indicate S1/S0 conical intersections (CIs) which provide non-adiabatic gates for radiation-less decay to the ground state. At the CI, barrier-free reaction coordinates direct the excited system to the ground state of enol-type minimum. According to calculation results, a trans- keto type structure obtained from photoexcitation of the enol, can be responsible for the photo chromoic effect of title compound. Furthermore, our results confirm the suggestion that aromatic Schiff Bases are potential candidates for optically driven molecular switches.