Theoretical mechanistic study of self-sensitized photo-oxygenation and singlet oxygen thermal release in a dimethyldihydropyrene derivative

The self-sensitized photo-oxygenation and singlet oxygen thermal release mechanisms in a pyridinium-substituted dimethyldihydropyrene (DHP) derivative have been investigated using quantum chemical calculations. First, the main photophysical pathway for intersystem crossing was identified, allowing the production of a DHP triplet state. Second, the energy transfer pathway between this triplet state and the oxygen triplet ground state was computed revealing a very efficient route for the photosensitized generation of singlet oxygen. Finally, the thermal pathway for the formation of a metacyclophanediene endoperoxide and the singlet oxygen release was characterized. A concerted and a stepwise mechanism were identified, the first one being lower in energy. All these results are consistent with recent experimental results and confirm that this type of system could be attractive oxygen carriers and singlet oxygen delivery agents.