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 (similar to 164%) of long-lived triplets (>300 mu s) is prepared and used to generate singlet oxygen (O-1(2)) and superoxide radicals (O-2(-)). Remarkably, O-1(2) and O-2(-) yields are boosted compared to the existing traditional PSs based on intersystem crossing (ISC). The O-1(2) yield reaches an unprecedented similar to 148%, representing the highest value ever reported so far. Thus, this SF PS shows an improved photooxidation activity over ISC PSs. Additionally, the O-1(2) and O-2(-) 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 O-1(2)/O-2(-) yield but also opens up a new field for the application of SF.