Quantum chemistry is used to design photoredox catalysts with desirable lifetimes, absorption wavelengths, reduction potentials and intramolecular charge transfer to catalyze atom transfer radical polymerization. Photoexcited intramolecular charge transfer (CT) states in <i>N,N</i>-diaryl dihydrophenazine photoredox catalysts are accessed through catalyst design and investigated through combined experimental studies and density functional theory (DFT) calculations. These CT states are reminiscent of the metal to ligand charge transfer (MLCT) states of ruthenium and iridium polypyridyl complexes. For cases where the polar CT state is the lowest excited state, we observed its population through significant solvatochromic shifts in emission wavelength across the visible spectrum by varying solvent polarity. The importance of accessing CT states for photoredox catalysis of atom transfer radical polymerization is hypothesized to enhance electron transfer for radical activation while minimizing non-productive back electron transfer and fluorescence. The influence of solvent polarity on the ion pairing strength between the oxidized photocatalyst and the bromide anion provides further evidence of the polymerization mechanism because it affects the radical deactivation pathway and thus the ability to realize a controlled radical polymerization. Greater understanding of these photoredox catalysts in CT and ion pairing enables their application toward the polymerization of methyl methacrylate for the synthesis of polymers with precisely tuneable molecular weights and dispersities typically lower than 1.10.          <br/><br/>

Design of photoredox catalysts for efficient organocatalyzed atom transfer radical polymerization

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.