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

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.