Flow Electrophotocatalysis in Organic Synthesis: Advantages and Challenges

In the past few years, the immense synthetic capability of electrophotocatalysis, the hybrid methodology of electrochemistry and photochemistry, has been realized owing to advancements in each field over the past couple of decades. This has been driven by the desire to obtain more efficient and sustainable synthetic practices, which is made possible by using two of the most abundant and well-known substances as traceless reagents, namely electrons and photons. It has been realized that while electrosynthesis and photoredox catalysis are imperfect, their respective strengths can nearly perfectly compensate for the weaknesses of the other. Moreover, continuous flow chemistry has also emerged as an improved strategy in which to conduct chemical transformations, particularly in terms of reaction screening and scale-up. In this review, we cover advancements in electrophotocatalysis but do so while predominantly focusing on those conducted through continuous flow reactors. This is then taken a step further by taking an engineering approach to reactor design. We discuss two configurations of reactor setups, one in which multiple photo- and electrochemical reactors are connected in series, termed “Sequential Electrophotochemical Flow”, and the other in which the design and materials of a single reactor are such that electrochemical and photochemical reactions occur simultaneously, termed “Electrophotochemical Flow with Transparent Electrodes”. The examples associated with each are taken from academic works for the purposes of proof of concept and reaction scope; where available, they are compared to a batch counterpart.