title: Excitation-wavelength-dependent, ultrafast photoinduced electron transfer in bisferrocene/BF2-chelated-azadipyrromethene/fullerene tetrads.
abstract: Donor-acceptor distance, orientation, and photoexcitation wavelength are key factors in governing the efficiency and mechanism of electron-transfer reactions both in natural and synthetic systems. Although distance and orientation effects have been successfully demonstrated in simple donor-acceptor dyads, revealing excitation-wavelength-dependent photochemical properties demands multimodular, photosynthetic-reaction-center model compounds. Here, we successfully demonstrate donor- acceptor excitation-wavelength-dependent, ultrafast charge separation and charge recombination in newly synthesized, novel tetrads featuring bisferrocene, BF2 -chelated azadipyrromethene, and fullerene entities. The tetrads synthesized using multistep synthetic procedure revealed characteristic optical, redox, and photo reactivities of the individual components and featured "closely" and "distantly" positioned donor-acceptor systems. The near-IR-emitting BF2-chelated azadipyrromethene acted as a photosensitizing electron acceptor along with fullerene, while the ferrocene entities acted as electron donors. Both tetrads revealed excitation-wavelength-dependent, photoinduced, electron-transfer events as probed by femtosecond transient absorption spectroscopy. That is, formation of the Fc(+)-ADP-C60(.-) charge-separated state upon C60 excitation, and Fc(+)-ADP(.-)-C60 formation upon ADP excitation is demonstrated.
authors.affiliation: Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, TX 76203-5017, USA.
authors.forename: Venugopal
authors.initials: V
authors.lastname: Bandi
authors.forename: Mohamed E
authors.initials: ME
authors.lastname: El-Khouly
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Nesterov
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Zandler
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza
mesh_terms: D001896:Boron Compounds / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004579:Electron Transport; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D000075163:Metallocenes; D008956:Models, Chemical; D055668:Photochemical Processes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D002614:Chelating Agents; D005296:Ferrous Compounds; D037741:Fullerenes; D000075163:Metallocenes; D045322:Photosynthetic Reaction Center Complex Proteins; C069837:fullerene C60; C004998:ferrocene