Organic semiconductor photocatalyst does double duty

Light-activated catalysts are increasingly used in reduction-oxidation reactions, generating radicals that selectively modify complex molecules. But most such photoredox catalysts rely on expensive, scarce metals like iridium and rubidium. Many are vulnerable to harsh reagents, and different reactions usually need custom catalysts. Chemists in Germany have developed an alternative that not only is cheap and stable but also can catalyze a broad range of radical-based redox reactions. The catalyst is a solid semiconductor material called mesoporous graphitic carbon nitride, an extended network of triazine-based aromatic rings that is easily prepared from cyanamide (Science 2019, DOI: 10.1126/science.aaw3254). “We believe it offers a significant improvement,” says Burkhard König at the University of Regensburg, part of the research team. Blue light separates charges on the catalyst’s surface, generating electrons that drive reduction reactions, and holes that handle oxidation reactions. This allows the catalyst to simultaneously add different chemical groups—from more than 20 options—to two distinct carbon-hydrogen sites in a wide range of aromatic molecules, such as pharmaceuticals, hormones, and other bioactive compounds (example reaction shown). Untroubled by extreme pHs or intense light, the solid catalyst was easily recovered by filtration or centrifugation and could be reused at least four times.