Benchmarking Density Functionals for Ground- and Excited-State Reduction and Oxidation Potentials of Organic...

Photoredox catalysis enables chemical reactions under mild reaction conditions; single-electron transfer is a common key step. Quantum mechanical calculations has accelerated the increasing numbers of photoredox catalysts because of its straightforward implementation in many softwares. Unfortunately, computing the redox potentials of molecular excited states is difficult. While density functional theory (DFT) offers a cost-effective way to compute ground- and excited-state redox potentials, a benchmarking study identifying the best density functional has not yet been conducted. In this report, we evaluate 147 combinations of density functionals and basis sets (i.e., model chemistries) to compute the S₀, S₁, and T₁ reduction and oxidation potentials for nine organic photoredox catalysts (cyanoarenes, benzophenones, xanthenes, and acridinium) with experimentally determined ground- and excited-state redox potentials. We provide recommendations for predicting ground- and excited-state reduction and oxidation potentials. We find that the best model chemistry for excited-state reduction and oxidation potentials, with PBE0-D3BJ/6-311+G(d,p) and N12-SX/6-311+G(d,p) excelling for S₁ states and ωB97X/6-311+G(d,p) and BHandH/6-311+G(d,p) perform best for T₁ states. Guidance is provided for balancing accuracy and CPU time, especially for T₁ and S₁ redox potentials.