title: Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines as Photoredox Catalysts.
abstract: N-Aryl phenoxazines have been synthesized and introduced as strongly reducing metal-free photoredox catalysts in organocatalyzed atom transfer radical polymerization for the synthesis of well-defined polymers. Experiments confirmed quantum chemical predictions that, like their dihydrophenazine analogs, the photoexcited states of phenoxazine photoredox catalysts are strongly reducing and achieve superior performance when they possess charge transfer character. We compare phenoxazines to previously reported dihydrophenazines and phenothiazines as photoredox catalysts to gain insight into the performance of these catalysts and establish principles for catalyst design. A key finding reveals that maintenance of a planar conformation of the phenoxazine catalyst during the catalytic cycle encourages the synthesis of well-defined macromolecules. Using these principles, we realized a core substituted phenoxazine as a visible light photoredox catalyst that performed superior to UV-absorbing phenoxazines as well as previously reported organic photocatalysts in organocatalyzed atom transfer radical polymerization. Using this catalyst and irradiating with white LEDs resulted in the production of polymers with targeted molecular weights through achieving quantitative initiator efficiencies, which possess dispersities ranging from 1.13 to 1.31.
authors.affiliation: Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, and §Materials Science and Engineering Program, University of Colorado Boulder , Boulder, Colorado 80309, United States.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Pearson
authors.affiliation: Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, and §Materials Science and Engineering Program, University of Colorado Boulder , Boulder, Colorado 80309, United States.
authors.forename: Chern-Hooi
authors.initials: CH
authors.lastname: Lim
authors.affiliation: Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, and §Materials Science and Engineering Program, University of Colorado Boulder , Boulder, Colorado 80309, United States.
authors.forename: Blaine G
authors.initials: BG
authors.lastname: McCarthy
authors.affiliation: Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, and §Materials Science and Engineering Program, University of Colorado Boulder , Boulder, Colorado 80309, United States.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Musgrave
authors.affiliation: Department of Chemistry and Biochemistry, ‡Department of Chemical and Biological Engineering, and §Materials Science and Engineering Program, University of Colorado Boulder , Boulder, Colorado 80309, United States.
authors.forename: Garret M
authors.initials: GM
authors.lastname: Miyake
mesh_terms: D002384:Catalysis; D004579:Electron Transport; D008958:Models, Molecular; D008968:Molecular Conformation; D010078:Oxazines / Q000737:chemistry*; D055668:Photochemical Processes; D058105:Polymerization
chemical_list: D010078:Oxazines; C039203:phenoxazine