title: Intramolecular Charge Transfer and Ion Pairing in N,N-Diaryl Dihydrophenazine Photoredox Catalysts for Efficient Organocatalyzed Atom Transfer Radical Polymerization.
abstract: Photoexcited intramolecular charge transfer (CT) states in N,N-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 energy excited state, we observe its population through significant solvatochromic shifts in emission wavelength across the visible spectrum by varying solvent polarity. We propose the importance of accessing CT states for photoredox catalysis of atom transfer radical polymerization lies in their ability to minimize fluorescence while enhancing electron transfer rates between the photoexcited photoredox catalyst and the substrate. Additionally, solvent polarity influences the deactivation pathway, greatly affecting the strength of ion pairing between the oxidized photocatalyst and the bromide anion and thus the ability to realize a controlled radical polymerization. Greater understanding of these photoredox catalysts with respect to CT and ion pairing enables their application toward the polymerization of methyl methacrylate for the synthesis of polymers with precisely tunable molecular weights and dispersities typically lower than 1.10.
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: Matthew D
authors.initials: MD
authors.lastname: Ryan
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: Jordan C
authors.initials: JC
authors.lastname: Theriot
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: Steven M
authors.initials: SM
authors.lastname: Sartor
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: Niels H
authors.initials: NH
authors.lastname: Damrauer
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.identifier: 0000-0003-2451-7090
authors.initials: GM
authors.lastname: Miyake
mesh_terms: D002384:Catalysis; D004579:Electron Transport; D005453:Fluorescence; D005609:Free Radicals / Q000138:chemical synthesis / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010619:Phenazines / Q000737:chemistry*; D055668:Photochemical Processes; D058105:Polymerization; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D005609:Free Radicals; D007477:Ions; D009942:Organometallic Compounds; D010619:Phenazines; D011108:Polymers