Interexcited State Photophysics II: A Qualitative Excited State Dynamics Model from First-Principles

In Part <b>I</b> of this series [<i>J. Chem. Theory Comput.</i> <b>2023</b>, <i>19</i>(1), 271-292], a benchmarking study of nuclear-electronic couplings was performed using 15 density functionals across two basis sets. From these, five density functional and basis set combinations (data sets) yielded results that agreed with experiments for the <i>S</i>₁ → <i>S</i>₀ internal conversion (IC) rate in perylene. In this Part II, we use those five data sets to calculate the excited state dynamics in perylene up to the second excited state within a density functional theory (DFT) framework. Interexcited state IC was found to be generally overestimated by 10 orders of magnitude at ∼10²⁰ s^-1 in the best case for the <i>S</i>₂ → <i>S</i>₁ pathway. Probing of the methodology using a multireference method found DFT to overestimate the nuclear-electronic coupling between excited states, with CASSCF(8,8) overestimating the IC rate by 3 orders of magnitude in the best case. Therefore, we applied a faux-damping function, which reduced the rates by 10 orders of magnitude on the singlet manifold and 20 on the triplet manifold. With this correction, the IC rate constants for <i>S</i>₂ → <i>S</i>₁ compared well to the experimental value of 302 ± 5 fs calculated in this work. Photoluminescence quantum yields (PLQYs) and anti-Kasha quantum yields (AKQYs) were calculated; the PBE0/def2-TZVP data set yielded the most accurate PLQY and AKQY (0.907 and 5.07 × 10^-5, respectively). Although there is room for refinement in the method, we have shown a qualitative prediction of the excited state dynamics of perylene.