Watching a Full Photocatalytic Cycle by Electron Paramagnetic Resonance

Molecular photocatalysis has shown tremendous success in sustainable energy and chemical synthesis. However, visualizing the intricate mechanisms in photocatalysis is a significant and long-standing challenge. By employing our recently developed sensitivity-enhanced time-resolved electron paramagnetic resonance technique, we directly observed all radicals and radical ions involved in the photocatalytic addition of a tertiary amine to tert-butyl acrylate. The full picture of the photocatalytic cycle has been vividly illustrated by the fine structures, chemical kinetics, and dynamic spin polarization of all open-shell intermediates directly observed in this prototypical system. Given the universality of this methodology, we believe it greatly empowers the research paradigm of direct observation in both photocatalysis and radical chemistry.