Electronic couplings for singlet oxygen photosensitization and its molecular orbital overlap description

The reaction of triplet fusion, also named triplet-triplet annihilation, has attracted a lot of research interests because of its wide applications in photocatalytic, solar cells, and bioimaging. As for the singlet oxygen photosensitization, the reactive singlet oxygen species are generated through the energy transfers from photosensitizer (PS) to ground triplet oxygen molecule. In this work, we computed the electronic coupling for singlet oxygen photosensitization using the nonadiabatic coupling from the quantum chemical calculation. Then we utilized the molecular orbital (MO) overlaps to approximate it, where the MOs were computed from isolated single molecules. As demonstrated with quantitative results, this approach well describes the distribution of the coupling strength as the function of the intermolecular distance between the sensitizer and O2, providing us a simple but effective way to predict the coupling of triplet fusion reactions.