title: Artificial photosynthetic reaction center with a coumarin-based antenna system.
abstract: In photosynthesis, sunlight is absorbed mainly by antenna chromophores that transfer singlet excitation energy to reaction centers for conversion to useful electrochemical energy. Antennas may likewise be useful in artificial photosynthetic systems that use sunlight to make fuels or electricity. Here, we report the synthesis and spectroscopic properties of a molecular hexad comprising two porphyrin moieties and four coumarin antenna chromophores, all organized by a central hexaphenylbenzene core. Light absorbed by any of the coumarins is transferred to a porphyrin on the 1-10 ps time scale, depending on the site of initial excitation. The quantum yield of singlet energy transfer is 1.0. The energy transfer rate constants are consistent with transfer by the Förster dipole-dipole mechanism. A pyridyl-bearing fullerene moiety self-assembles to the form of the hexad containing zinc porphyrins to yield an antenna-reaction center complex. In the resulting heptad, energy transfer to the porphyrins is followed by photoinduced electron transfer to the fullerene with a time constant of 3 ps. The resulting P(•+)-C60(•-) charge-separated state is formed with an overall quantum yield of 1.0 and decays with a time constant of 230 ps in 1,2-difluorobenzene as the solvent.
authors.affiliation: Department of Chemistry and Biochemistry, Center for Bio-Inspired Solar Fuel Production, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: Vikas
authors.initials: V
authors.lastname: Garg
authors.forename: Gerdenis
authors.initials: G
authors.lastname: Kodis
authors.forename: Paul A
authors.initials: PA
authors.lastname: Liddell
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Terazono
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Moore
authors.forename: Ana L
authors.initials: AL
authors.lastname: Moore
authors.forename: Devens
authors.initials: D
authors.lastname: Gust
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry* / Q000378:metabolism; D003374:Coumarins / Q000737:chemistry*; D004579:Electron Transport; D004735:Energy Transfer; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D011166:Porphyrins / Q000737:chemistry; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D001672:Biocompatible Materials; D003374:Coumarins; D045322:Photosynthetic Reaction Center Complex Proteins; D011166:Porphyrins; C030123:coumarin