Individual Marcus-type kinetics controls singlet and triplet oxygen evolution from superoxide

Oxygen evolution from superoxide is a critical aspect of oxygen redox chemistry. However, the factors determining the formation of often harmful singlet oxygen are unclear. Here, we report that the release of triplet or singlet oxygen is governed by individual Marcus normal and inverted region behavior. Using a wide range of chemical oxidants, we found that as the driving force increases, the initially dominant evolution of triplet oxygen slows down, and singlet oxygen evolution becomes predominant with higher maximum kinetics. This behavior also applies to superoxide disproportionation, the oxidation of one superoxide by another, in both non-aqueous and aqueous systems, where Lewis and Brønsted acidity control driving forces. Our findings suggest ways to understand and control spin states and kinetics in oxygen redox chemistry.