<i>ETHos</i> – A Swiss‐Made Open‐Source Modular Photoreactor for Laboratory‐Scale Photochemical Reactions

Abstract The emergence of photoredox chemistry has enabled the development of previously inaccessible synthetic transformations. Despite the popularity of photoredox chemistry, commercial photoreactors remain expensive. As a result, most academic research groups resort to self‐built, not easily replicable reactor designs, jeopardizing the reproducibility and accessibility of photochemical research. To address these issues, this work introduces an easily replicable and modular open‐source photoreactor optimized for lab‐scale photochemical synthesis. The reactor is operationally simple, operates consistently and reproducibly, and is inexpensive to manufacture. Our design integrates active temperature regulation, an exchangeable vial rack, and customizable light sources into a hybrid structure of machined aluminum, 3D‐printed parts, and commercially available components. The open‐source reactor with detailed 3D CAD files on GitHub is designed to make research in the field of photochemistry more accessible and reproducible.