title: Laser-Induced Dynamics of Peroxodicopper(II) Complexes Vary with the Ligand Architecture. One-Photon Two-Electron O2 Ejection and Formation of Mixed-Valent Cu(I)Cu(II)-Superoxide Intermediates.
abstract: Photoexcitation of end-on trans-μ-1,2-peroxodicopper(II) complex [(tmpa)2Cu(II)2(O2)](2+) (1) (λmax = 525 and 600 nm) and side-on μ-η(2):η(2)-peroxodicopper(II) complexes [(N5)Cu(II)2(O2)](2+) (2) and [(N3)Cu(II)2(O2)](2+) (3) at -80 °C in acetone led to one-photon two-electron peroxide-to-dioxygen oxidation chemistry (O2(2-) + hν → O2 + 2e(-)). Interestingly, light excitation of 2 and 3 (having side-on μ-η(2):η(2)-peroxo ligation) led to release of dioxygen, while photoexcitation of 1 (having an end-on trans-1,2-peroxo geometry) did not, even though spectroscopic studies revealed that both reactions proceeded through previously unknown mixed-valent superoxide species: [Cu(II)(O2(•-))Cu(I)](2+) (λmax = 685-740 nm). For 1, this intermediate underwent further fast intramolecular electron transfer to yield an "O2-caged" dicopper(I) adduct, Cu(I)2-O2, and a barrierless stepwise back electron transfer to regenerate 1 occurred. Femtosecond laser excitation of 2 and 3 under the same conditions still led to [Cu(II)(O2(•-))Cu(I)](2+) intermediates that, instead, underwent O2 release with a quantum yield of 0.14 ± 0.1 for 3. Such remarkable differences in reaction pathways likely result from the well-known ligand-derived stability of 2 and 3 vs 1 indicated by ligand-Cu(II/I) redox potentials; (N5)Cu(I) and (N3)Cu(I) complexes are far more stable than (tmpa)Cu(I) species. The fast Cu(I)2/O2 rebinding kinetics was also measured after photoexcitation of 2 and 3, with the results closely tracking those known for the dicopper proteins hemocyanin and tyrosinase, for which the synthetic dicopper(I) precursors [(N5)Cu(I)2](2+) and [(N3)Cu(I)2](2+) and their dioxygen adducts serve as models. The biological relevance of the present findings is discussed, including the potential impact on the solar water splitting process.
authors.affiliation: Department of Chemistry, The Johns Hopkins University , Baltimore, Maryland 21218, United States.
authors.forename: Claudio
authors.initials: C
authors.lastname: Saracini
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA and SENTAN, Japan Science and Technology Agency (JST) , Suita, Osaka 565-0871, Japan.|Department of Chemistry and Nano Science, Ewha Womans University , Seoul 120-750, Korea.
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA and SENTAN, Japan Science and Technology Agency (JST) , Suita, Osaka 565-0871, Japan.
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Suenobu
authors.affiliation: Department of Chemistry, The Johns Hopkins University , Baltimore, Maryland 21218, United States.
authors.forename: Gerald J
authors.initials: GJ
authors.lastname: Meyer
authors.affiliation: Department of Chemistry, The Johns Hopkins University , Baltimore, Maryland 21218, United States.
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA and SENTAN, Japan Science and Technology Agency (JST) , Suita, Osaka 565-0871, Japan.|Department of Chemistry and Nano Science, Ewha Womans University , Seoul 120-750, Korea.|Faculty of Science and Engineering, Meijo University, ALCA and SENTAN, Japan Science and Technology Agency (JST) , Nagoya, Aichi 468-0073, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
mesh_terms: D003300:Copper / Q000737:chemistry*; D007700:Kinetics; D007834:Lasers; D008024:Ligands; D010100:Oxygen / Q000737:chemistry*; D017785:Photons; D013481:Superoxides / Q000737:chemistry*
chemical_list: D008024:Ligands; D013481:Superoxides; D003300:Copper; D010100:Oxygen