title: Photodynamics of Schiff base salicylideneaniline: trajectory surface-hopping simulations.
abstract: We report a computational study on the photochemistry of the prototypical aromatic Schiff base salicylideneaniline in the gas phase using static electronic structure calculations (TDDFT, OM2/MRCI) and surface-hopping dynamics simulations (OM2/MRCI). Upon photoexcitation of the most stable cis-enol tautomer into the bright S1 state, we find an ultrafast excited-state proton transfer that is complete within tens of femtoseconds, without any C═N double bond isomerization. The internal conversion of the resulting S1 cis-keto species is initiated by an out-of-plane motion around the C-C single bond, which guides the molecule toward a conical intersection that provides an efficient deactivation channel to the ground state. We propose that the ease of this C-C single bond rotation regulates fluorescence quenching and photocoloration in condensed-phase environments. In line with previous work, we find the S1 cis-keto conformer to be responsible for fluorescence, especially in rigid surroundings. The S0 cis-keto species is a transient photoproduct, while the stable S0 trans-keto photoproduct is responsible for photochromism. The trajectory calculations yield roughly equal amounts of the S0 cis-enol and trans-keto photoproducts. Methodologically, full-dimensional nonadiabatic dynamics simulations are found necessary to capture the preferences among competitive channels and to gain detailed mechanistic insight into Schiff base photochemistry.
authors: Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
authors: Lasse
authors: L
authors: Spörkel
authors: Ganglong
authors: G
authors: Cui
authors: Walter
authors: W
authors: Thiel