1.5 Photochemistry and Radical Generation: Approaches in Mechanism Elucidation

Abstract

The development of photocatalytic reactions has reemerged as an active area of research in organic synthesis. A large variety of synthetically valuable transformations have now been developed that take advantage of the ease by which photocatalysts generate a variety of open-shelled reactive intermediates. The study of the mechanisms of these reactions, however, is a challenge, especially in increasingly sophisticated reactions that often involve multiple steps and complex reaction mixtures. Multiple complementary techniques often need to be utilized in tandem in order to develop a detailed understanding of these reactions. The first part of this review outlines many of the most common techniques that are used to interrogate the initiation and product-formation steps of a photocatalytic transformation. The second part describes case studies that provide contextual examples of how photophysical, electrochemical, physical organic, and computational investigations can be used together to provide insights into the mechanisms of complex photocatalytic reactions.

Key words

radicals - photochemistry - photochemical - mechanism - quenching - absorption - emission - electrochemistry - excited-state potential - UV-vis - transient absorption - time resolved - Stern–Volmer - quantum yield - hydrogen-atom transfer (HAT) - proton-coupled electron transfer (PCET) - metallaphotoredox - EDA complexes - enantioselectivity - chiral photocatalysts - cycloaddition - initiation - propagation

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