Engineering Cyanoarene Photocatalysts to Resolve Deactivation Challenges in Organocatalyzed ATRP

Cyanoarene-based photocatalysts (PCs) have been widely utilized in organic transformations including photo-mediated controlled radical polymerization (CRP). Despite favorable photophysical and electrochemical properties, these PCs have exhibited limited efficacy in photoinduced organocatalyzed ATRP (O-ATRP). We identified that reduced performance arises from preferential formation of [PC^•+…Br^-] complexes, which facilitates detrimental back electron transfer (BET), generating bromine radicals and side reactions. To address this, we developed a new cyanoarene-based PC, 4DMDP-IPN, incorporating strongly electron-donating groups at donor moieties. This design effectively suppresses complex formation and alleviates BET, significantly improving O-ATRP performance. With 4DMDP-IPN, O-ATRP of methacrylates with high monomer conversion, narrow dispersity, and excellent chain-end fidelity, even at an ultra-low PC loading of 5 ppm. This represents the lowest reported PC loading that still ensures polymerization control, eliminating the need for post-polymerization catalyst removal. Moreover, we demonstrated successful O-ATRP of poly(methyl acrylate), a particularly challenging monomer, with decent levels of control and chain-end fidelity. This work not only overcomes intrinsic limitations of cyanoarene-based PCs in O-ATRP, but also establishes a new design strategy for next-generation PCs. We anticipate that these findings will contribute significantly to the advancement of photo-CRP and broaden the applicability of cyanoarene-based PCs in a wide range of organic transformations.