In recent years, in-situ generated organic radicals have been used as highly potent photoinduced electron transfer (PET) agents resulting in catalytic systems as reducing as alkaline metals that can activate remarkably stable bonds. However, the transient nature of these doublet state open-shell species has led to debatable mechanistic studies, hindering adoption and development. Herein, we document the use of an isolated and stable neutral organic radical as a highly photoreducing species with a reduction potential lower than – 3.5 V vs SCE. The isolated radical offers a unique platform to investigate the mechanism behind the photocatalytic activity of organic radicals. Our mechanistic study supports the involvement of solvated electrons formed by single electron transfer (SET) between the short-lived excited state organic radical and the solvent.
In this new version, we are mostly focusing on the mechanism involved during photocatalysis using organic radical as photocatalyst. As a result, we have remove some of the scope of transformation and added mechanistic experiments such as UV-VIs absorption and emission spectroscopy, Transient Absorption spectroscopy, characterization of intermediates and isotope scrambling experiments. This version of the manuscript offers a complete picture of the mechanism involved during consecutive photoelectron transfer (ConPET), and highlight the involvement of solvated electrons.
ESI for Isolated Neutral Helicene Radical Provides Insight into Consecutive Two-Photon Excitation Photocatalysis