Employing Singlet Fission into Boosting the Generation of Singlet Oxygen and Superoxide Radicals for Photooxidation Reactions

Developing highly efficient heavy-metal-free photosensitizers (PSs) for the production of reactive oxygen species (ROS) is urgent to achieve wide applications of ROS, yet it remains a great challenge. As a proof of concept, singlet fission (SF), possessing the exciton multiplication ability with a maximum 200% triplet yield, is employed to generate ROS. Herein, a metal-free tetracene dimer with a high yield (∼164%) of long-lived triplets (>300 μs) is prepared and used to generate singlet oxygen (1O2) and superoxide radicals (O2·–). Remarkably, 1O2 and O2·– yields are boosted compared to the existing traditional PSs based on intersystem crossing (ISC). The 1O2 yield reaches an unprecedented ∼148%, representing the highest value ever reported so far. Thus, this SF PS shows an improved photooxidation activity over ISC PSs. Additionally, the 1O2 and O2·– generation mechanisms are described clearly by combining TA spectra and controlled experiments. This represents the first example of utilizing the two triplet states produced by SF to generate ROS and catalyze related reactions. The work not only presents a strategy for generating and enhancing the 1O2/O2·– yield but also opens up a new field for the application of SF.