Using Density Functional Theory Based Methods to Investigate the Photophysics of Polycyclic Aromatic Hydrocarbon Radical Cations: A Benchmark Study on Naphthalene, Pyrene and Perylene Cations

Abstract

AbstractUnrestricted DFT (UDFT), time‐dependent DFT (TDDFT) and spin‐flip TDDFT (SF‐TDDFT) were used to investigate the potential energy surfaces of the ground and first two electronic excited states of the naphthalene, pyrene and perylene radical cations. In particular, conical intersections (which play a central role in the photophysics of these cations) were located with these DFT‐based methods. The results are consistent with accurate multiconfigurational wavefunction‐based ab initio methods. These show that naphthalene and pyrene cations can quickly relax nonradiatively from their excited states back down to the original ground state species through easily accessible conical intersections, but the perylene cation cannot do so, due to the absence of any accessible funnels between the lowest excited state and the ground state, leaving radiative decay as the most probable photophysical pathway. This study paves the way for using computationally efficient density functional theory (DFT)‐based methods in future investigations of the photophysics of much larger polycyclic aromatic hydrocarbons, for which multiconfigurational wavefunction‐based methods become prohibitively expensive.