文摘
The photophysics of 8-azaadenine (8-AA) has been studied with the CASPT2//CASSCF protocol and ANO-L double-味 basis sets. Stationary equilibrium structures, surface crossings, minimum energy paths, and linear interpolations have been used to study possible mechanisms to populate the lowest triplet state, T13(蟺蟺*), capable of sensitizing molecular oxygen. Our results show that two main mechanisms can occur after photoexcitation to the S21(蟺蟺*) state. The first one is through the S2/S1 conical intersection ((1蟺蟺*/1n蟺*)CI), leading to the S1 (1n蟺*) state minimum, (S1 (1n蟺*))min, where a singlet鈥搕riplet crossing, (1n蟺*/3蟺蟺*)STC, is accessible. The second one starts with the (1蟺蟺*/3n蟺*)STC at the (S2(1蟺蟺*))min, from which the system can evolve to the (T2 (3n蟺*))min, with subsequent population of the T1 excited electronic state, due to the (3n蟺*/3蟺蟺*)CI conical intersection.