<p>Singlet oxygen (<sup>1</sup>O<sub>2</sub>), a widely used reactive oxygen species (ROS) in industry and biomedical applications, plays a fundamental role throughout nature. We report a novel method to generate <sup>1</sup>O<sub>2</sub>selectively and efficiently through copper-based Fenton chemistry under circumneutral conditions enhanced by chloride as co-catalyst, with reactivity completely different than that observed in classical iron-based Fenton chemistry. The mechanism of its formation was elucidated through the kinetic studies of orthogonally reactive reporter molecules, i.e., singlet oxygen sensor green, 4-hydroxy-2,2,6,6-tetramethylpiperidine, and phenol, and selective ROS quenchers. This method selectively generates <sup>1</sup>O<sub>2</sub><i>in situ</i>neither relying on photosensitization nor resulting in side reactions, and together with the mechanistic understanding of the Cu-Fenton reaction, not only opens new possibilities in many industries, such as organic synthesis and antimicrobial treatments, but also provides insight into Cu and H<sub>2</sub>O<sub>2</sub>containing chemical, environmental, and biological systems.</p>
Singlet Oxygen Sensor Green is not a Suitable Probe for 1O2 in the Presence of Ionizing Radiation
