Photoinduced Storage and Thermal Release of Singlet Oxygen from 1,2-Dihydropyridine Endoperoxides

The quest for molecules able to trap, store, and release singlet oxygen is of utmost interest due to their applicability in various domains such as materials science and photomedicine. The aim of this study was to prepare and study a new family of singlet oxygen donors based on the 1,2-dihydropyridine motif. The experiments demonstrated the influence of substituents and solvents on the photooxygenation rate constants. The process can be operated reversibly by thermolysis of the in situ formed endoperoxide leading to a release of singlet oxygen and formation of the parent 1,2-dihydropyridine compound. A bifunctional structure based on a phenalenone photosensitizer covalently connected to a 1,2-dihydropyridine module was synthesized via a multi-step sequence. Upon irradiation with blue light, singlet oxygen was produced leading to the formation of the endoperoxide intermediate. In the dark cycle, the endoperoxide underwent cycloreversion reaction affording the parent 1,2-dihydropyridine unit paving the way to a continuous production of singlet oxygen during the light/dark cycles.