Visible Light‐Regulated Ring‐Opening Polymerization of Lactones by Employing Indigo as a Photoacid Catalyst

The development of visible light‐regulated polymerizations for precision synthesis of polymers has drawn considerable attention in the past years. In this study, an ancient dye, indigo, is successfully identified as a new and efficient photoacid catalyst, which can readily promote the ring‐opening polymerization of lactones under visible light irradiation in a well‐controlled manner, affording the desired polyester products with predictable molecular weights and narrow dispersity. The enhanced acidity of indigos by excitation is crucial to the H‐bonding activation of the lactone monomers. Chain extension and block copolymer synthesis are also demonstrated with this method.