Light has received increased attention for various chemical reactions but also in combination with biocatalytic reactions. Because currently only a few enzymatic reactions are known, which per se require light, most transformations involving light and a biocatalyst exploit light either for providing the cosubstrate or cofactor in an appropriate redox state for the biotransformation. In selected cases, a promiscuous activity of known enzymes in the presence of light could be induced. In other approaches, light-induced chemical reactions have been combined with a biocatalytic step, or light-induced biocatalytic reactions were combined with chemical reactions in a linear cascade. Finally, enzymes with a light switchable moiety have been investigated to turn off/on or tune the actual reaction. This Review gives an overview of the various approaches for using light in biocatalysis.

Photobiocatalysis is an alternative approach in synthesis that has received much attention in the recent years. Due to the youth of the topic, only few reactor systems are commercially available. To allow a parallel parameter‐screening approach as often used in the optimization of biocatalytic processes, a photoreactor was developed that can illuminate up to 24 samples at well‐defined reaction conditions. The device‘s optical features and temperature regulation have been thoroughly characterized and its application was demonstrated in four examples, specifically three photobiocatalytic and one photocatalytic process: (i) Light‐dependent decarboxylation using a photodecarboxylase; (ii) Reduction of protochlorophyllide using a protochlorophyllide oxidoreductase; (iii) Photosynthetic oxygen production performed by cyanobacteria; and (iv) (−)‐Riboflavin‐catalyzed (E/Z)‐isomerization of cinnamic acid derivatives.

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