Sensitization-Initiated Electron Transfer Mechanism in Photoredox Catalysis Using a Ru-Py Dyad as a Dual Sensitizer and Reductant

The sensitization-initiated electron transfer (SenI-ET) mechanism is a well-established concept in photoredox catalysis, yet its kinetic intricacies remain to be fully elucidated. In this study, we have successfully designed and synthesized a dyad, Ru(bpy)₃²⁺–pyrene (Ru-Py), which functions dually as a sensitizer and a reductant. By the use of the rapid intramolecular triplet and singlet energy transfer of Ru-Py, the complex decay pathway of the SenI-ET process was effectively simplified. Notably, we have demonstrated that direct electron transfer from ³Ru*-Py to diisopropyl ethylamine generates Ru(I)-Py, which further drives the catalytic process, rather than the catalytic reaction being driven by the formation of a Ru-Py^•- through electron transfer from Ru-³Py* to diisopropyl ethylamine. Furthermore, we employed Ru-Py as a catalyst for the C–H oxidation of an activated aryl bromide, demonstrating superior catalytic efficiency compared to that of the conventional Ru(bpy)₃²⁺/pyrene system.