Fluorescence of the perylene radical cation and an inaccessible D(0)/D(1) conical intersection: An MMVB, RASSCF, and TD-DFT computational study.

The photophysics of the perylene radical cation (Pe(+)) was studied using the molecular mechanics-valence bond (MMVB) hybrid force field. Potential energy surfaces of the first three electronic states were investigated. Geometry optimizations of critical points-including conical intersections between the relevant electronic states-were performed using the MMVB analytical energy gradient for cations. No accessible planar conical intersection between the D(0) and D(1) states of Pe(+) was found; this is consistent with the experimentally observed D(1) lifetimes and the observation of D(1) emission from this cation in the condensed phase. Benchmark RASSCF and TD-DFT calculations support the reliability of the MMVB results.