Tunable Aza-BODIPY Photocatalysts for Near-Infrared Metallaphotoredox Atom Transfer Radical Polymerization

Abstract The merger of photoredox and transition-metal catalysis has significantly advanced radical and redox transformations, yet its reliance on UV or visible light continues to limit applications in optically complex and spatially confined environments. Herein, we introduce a modular family of tetraaryl aza-boron-dipyrromethene (aza-BODIPY) organic photocatalysts (PCs) for near-infrared (NIR) metallaphotoredox atom transfer radical polymerization (ATRP). We systematically modulated peripheral electronics and core bromination, evaluating the dyes through quantum-chemical, electrochemical, and spectroscopic methods. This approach identified the key parameters governing catalytic performance: a delicate interplay between triplet-state accessibility, redox properties, and photostability. The optimized aza-BODIPY dye enables well-controlled ATRP of diverse acrylates and methacrylates at ultralow catalyst loadings, down to 5 ppm PC and 50 ppm copper complex. The system is further translated to open-air aqueous conditions, enabling rapid, high-throughput synthesis of water-soluble polymers in a 96-well plate format. Taking advantage of the enhanced penetration of NIR light, we demonstrate controlled polymerization through challenging physical barriers, including ex vivo tissue. Overall, this work defines design principles for far-red/NIR-absorbing aza-BODIPY PCs and expands the scope of NIR-mediated polymer synthesis to optically turbid, spatially restricted, and aqueous environments.