Reconfiguration of Active Species under Light for Enhanced Photocatalysis

Photocatalysis has emerged as a cornerstone of synthetic chemistry, enabling mild and selective transformations by using sustainable light sources. A common assumption persists that most photocatalysts are taken for granted to function as monomorphic species throughout the catalytic cycle. Our findings challenge this premise and discover a new mechanistic picture, demonstrating that the evolution of the catalyst under light is not a degradation artifact but a productive and exploitable transformation pathway. Using phenothiazine (PHT) as a model, we demonstrate that light triggers <i>in situ</i> formation of a diverse "cocktail" of catalytically active dimer, trimer, oligomers and their oxides with unique photophysical and redox properties. These reconfigured species expand the usable light spectrum, including red light, and exhibit better catalytic performance in oxidative coupling and sulfide oxidation reactions. The reconfigured catalysts unlock multiwave activation, driving oxidative coupling and sulfide oxidation reactions with remarkable efficiency (up to 99% yield) across UV to red light (λ = 650 nm), far beyond the capabilities of the parent PHT. We introduce the ReAct-Light concept (Reconfigurable Active species under Light) to capture this dynamic, wavelength-adaptive behavior. The work provides an example of key mechanistic insight into dynamic catalyst evolution, opening the way for the design of next-generation adaptive catalysts with enhanced efficiency.