Model Calculations on the Srereoseleethity of the Triplet Photoreaction of 1,2-Dimethyltriniethylene

摘要

In a nonadiabatic photoreaction, excitation from the ground state (S_0) into the lowest singlet state (S_1) or triplet state (T_1) brings about geometrical changes followed by return from S_1 to S_0 by a conical intersection or from T_1 to S_0 by intersystem crossing (ISC), and thermal equilibration in the ground state. Although the structures of the products and the efficiencies of their formation depend on the nature of the motions in the excited state, on the geometry of return to the S_0 state,and the final steepest descent motion on the S_0 surface, the geometry of return is of a paramount importance in solution reactions. For a nonadiabatic singlet reaction, this is the conical intersection, which from a mechanistic point of view plays a similar role as the transition state in a thermal reaction.