Emerging Activation Modes and Techniques in Visible-Light-Photocatalyzed Organic Synthesis

Abstract Visible light photocatalysis has evolved into a promising mild and sustainable strategy to access radicals. This field unlocks formerly challenging or even previously inaccessible organic transformations. In this review, an overview of some lesser-known modes of photochemical activation of organic molecules and several emerging techniques within the versatile field of visible light photocatalysis are discussed. These are illustrated by selected photocatalytic reactions, with particular attention given to the reaction mechanism. 1 Introduction 2 Advanced Photoactivation Modes 2.1 Photoinduced Hydrogen-Atom Transfer 2.2 Proton-Coupled Electron Transfer 2.3 Electron Donor-Acceptor Photoactivation of Organic Substrates 2.4 Excited-State Transition Metal Catalysis 3 Emerging Techniques 3.1 Dual Catalysis 3.2 Excited Radical Ion Photocatalysis 3.3 Upconversion Strategies and Other Two-Photon Mechanisms 3.4 Red and Near-Infrared Photocatalysis 4 Conclusions and Outlook