Atom-transfer radical polymerization, or ATRP, has proven to be a popular process for making polymers. The reaction uses a catalyst to reversibly generate a radical from an alkyl halide initiator. This radical then goes on to react with the double bond of a monomer, such as styrene or methyl methacrylate, a reaction that propagates until the monomer supply is exhausted. ATRP offers precise control over polymer chain growth, but the metal catalysts usually used are tough to remove, making most of the synthesized polymers unsuitable for biomedical or electronics applications. In recent years, chemists have developed organic catalysts for ATRP, but these require ultraviolet light to activate them and aren’t as good as metal catalysts at making certain types of polymers. Garret M. Miyake and colleagues of the University of Colorado, Boulder, now report an organocatalyzed ATRP that’s driven by visible light (Science 2016, DOI: 10.1126/science.aaf3935). Because the reaction runs with visible light, sunlight can mediate the reaction instead of UV lamps, thereby cutting costs. Miyake’s team used computational studies to develop its diaryl dihydrophenazine catalysts (example shown). These catalysts work as well as their metal catalyst counterparts for ATRP of methyl methacrylate.