Over the last decade, photoinduced atom transfer radical polymerization (photo-ATRP) techniques have been developed to harness the energy of light to generate radicals. Most of these methods require the use of UV light to initiate polymerization. However, UV light has several disadvantages: it can degrade proteins, damage DNA, cause undesirable side reactions, and has low penetration depth in reaction media.
In the present work, we have developed a dual photoredox/copper catalysis that allowed a well-controlled ATRP under low-energy green light. Eosin Y (EY) was used as an organic photocatalyst to trigger and drive the polymerization, while the copper species provided control over the radical propagation via ATRP equilibrium. Importantly, no polymer formation was observed in the absence of EY. In this dual catalysis, photoexcited EY undergoes reductive quenching by the ATRP ligand to form the EY radical anion (EY^●⁻). The EY^●⁻ reduces Cu^II/L by single electron transfer, leading to the formation of the Cu^I/L activator. Since Cu^I/L and EY^●⁻ can react with molecular oxygen, the continuous regeneration of the activator and the generation of EY radical anion itself provide high oxygen tolerance, allowing ATRP in an open vessel at stirring rates up to 1000 rpm. This method proved to be highly efficient for the synthesis of polymers without the need for deoxygenation. We envision that this versatile method will greatly facilitate the synthesis of complex polymeric materials by non-experts.

Sushil Lathwal

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