Recent advances in photoredox catalytic transformations by using continuous-flow technology

Photoredox catalysis is regarded as an economically appealing method for highly efficient and sustainable chemical syntheses. Nevertheless, numerous recent studies have revealed several unresolved disadvantages; for example, based on the Bouguer-Lambert-Beer law, the short propagation distance of photons in traditional batch reactors hampers the scalability of photocatalytic reactions. The introduction of continuous-flow technology for photochemical synthesis has resolved several of these problems. The use of photochemistry in microreactors has resulted in various transformations. Superior mixing ability, more effective heat transfer, and the easier magnification of continuous-flow chemical reactions are key to its success. Continuous-flow technology has allowed the optimization of several different types of conversion. Photoredox catalysts are effective under various reaction conditions because of their single-electron transfer properties. Common photocatalysts include transition metal complexes containing ruthenium, iridium, copper, iron, or manganese; organic photocatalysts; and heterogeneous photocatalysts. This review covers the types of photocatalysts that have recently been used in continuous-flow photochemistry.