Organocatalyzed atom transfer radical polymerization (O-ATRP) is a controlled radical polymerization methodology mediated by an organic photoredox catalyst, enabling light to drive the synthesis of polymers with defined composition and architecture. Unique to other photoredox catalyzed variants of this polymerization method, O-ATRP employs organic catalysts rather than transition metal-containing catalysts, providing several benefits. For example, O-ATRP avoids issues with metal contamination from residual catalyst which can limit the application scope of polymers synthesized using these methods. In addition, O-ATRP presents a more sustainable platform for polymer synthesis since it avoids the use of precious-metal containing catalysts and renewable, solar energy can be used to drive the reaction.
While O-ATRP exhibits several advantages over metal catalyzed polymerization methods, the use of organic catalysts to activate polymer chains through a photoinduced electron transfer mechanism presents several challenges. In particular, to engage in the necessary redox reactions to catalyze O-ATRP an organic molecule must exhibit certain photophysical and electrochemical properties. Moreover, compared to their metal counterparts, organic catalysts have been less well studied in this domain so there remains a need to design new organic photoredox catalysts and understand their reactivity.
In pursuit of designing new organic photoredox catalysts and understanding their reactivity in O-ATRP, our group reported perylene as the first visible-light absorbing O-ATRP catalyst in 2014. Since then we have studied N,N-diaryl dihydrophenazines and N-aryl phenoxazines as O-ATRP catalysts which exhibit superior performance compared with the initial perylene system. Our ongoing work in this area lies at the interface of organic, computational, photophysical, and polymer chemistries with continued understanding of these systems stemming from our interdisciplinary approach.