Time–oxygen & light indicating via photooxidation mediated up-conversion
Photooxidation is a major threat to perishable products. Therefore, an effective monitoring system for photooxidation reactions is urgently needed due to safety concerns. Herein, a time–oxygen & light indicator (TOLI) from a non-emissive stealth upconversion system is demonstrated to address this issue. Under photooxidation stress, a nonluminous precursor 9,10-bis(diphenylphosphino)anthracene (M1) is photo-oxidized to an efficient emitter 9,10-bis(diphenylphosphoryl)anthracene (M2), and triplet–triplet annihilation (TTA)-based upconversion emission is observed. The reaction rate is easily tunable and responsive to oxygen concentration and light intensity. Over a period of time, the enhanced emission related to the degree of photooxidation is ultimately used as an indicating signal. Thus a TOLI based on the TTA-upconversion process is achieved. This work not only develops a rational approach to the visualization and monitoring of photooxidation, but also demonstrates the varied control of the TTA-upconversion process.