Photo‐RAFT Polymerization Under Microwatt Irradiation via Unimolecular Photoinduced Electron Transfer

Abstract Photoinduced radical addition fragmentation chain transfer (PET‐RAFT) polymerization typically requires high light intensity (>5 mW cm − 2 ), limiting energy efficiency, and scalability. We demonstrate that adding a base to PET‐RAFT systems drastically enhances the reactivity of acidic chain transfer agents (CTAs) with Zn‐based photocatalysts (Zn porphyrin and Zn phthalocyanine). This approach enables complete polymerization under microwatt light intensity (0.25 mW cm − 2 ), a significant improvement over traditional PET‐RAFT, which showed no conversion under the same conditions. Both acrylates and methacrylates polymerized efficiently with excellent chain‐end fidelity. Reactivity was triggered chemically (via base addition) or electrochemically (via electrolytic reduction). Mechanistic studies reveal that base addition promotes a CTA‐Zn photocatalyst complex, shifting the activation from bimolecular to more efficient unimolecular PET‐RAFT.