| 1. |
- Duan, Lele, et al.
(författare)
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Isolated Seven-Coordinate Ru(IV) Dimer Complex with HOHOH (-) Bridging Ligand as an Intermediate for Catalytic Water Oxidation
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:30, s. 10397-
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Tidskriftsartikel (refereegranskat)abstract
- With the inspiration from an oxygen evolving complex (OEC) in Photosystern II (PSII), a mononuclear Ru(II) complex with a tetradentate ligand containing two carboxylate groups has been synthesized and structurally characterized. This Ru(II) complex showed efficient catalytic properties toward water oxidation by the chemical oxidant cerium(IV) ammonium nitrate. During the process of catalytic water oxidation, Ru(III) and Ru(IV) species have been successfully isolated as intermediates. To our surprise, X-ray crystallography together with HR-MS revealed that the Ru(IV) species is a seven-coordinate Ru(IV) dimer complex containing a [HOHOH](-) bridging ligand. This bridging ligand has a short O center dot center dot center dot O distance and is hydrogen bonded to two water molecules. The discovery of this very uncommon seven-coordinate Ru(IV) dimer together with a hydrogen bonding network may contribute to a deeper understanding of the mechanism for catalytic water oxidation. It will also provide new possibilities for the design of more efficient catalysts for water oxidation, which is the key step for solar energy conversion into hydrogen by tight-driven water splitting, the ultimate challenge in artificial photosynthesis.
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| 2. |
- Nonomura, Kazuteru, et al.
(författare)
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The effect of UV-irradiation (under short-circuit condition) on dye-sensitized solar cells sensitized with a Ru-complex dye functionalized with a (diphenylamino)styryl-thiophen group
- 2009
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Ingår i: International Journal of Photoenergy (Online). - : Hindawi Limited. - 1110-662X .- 1687-529X. ; :471828
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Tidskriftsartikel (refereegranskat)abstract
- A new ruthenium complex, cis-di(thiocyanato)(2,2'-bipyridine-4,4'-dicarboxylic acid)(4,4'-bis(2-(5-(2-(4-diphenylaminophenyl) ethenyl)-thiophen-2-yl)ethenyl)-2,2'-bipyridine)ruthenium(II) (named E322) has been synthesized for use in dye-sensitized solar cells (DSCs). Higher extinction coeff. and a broader absorption compared to the std. Ru-dye, N719, were aimed. DSCs were fabricated with E322, and the efficiency was 0.12% initially (4.06% for N719, as ref.). The efficiency was enhanced to 1.83% by exposing the cell under simulated sunlight contg. UV-irradn. at short-circuit condition. The reasons of this enhancement are (1) enhanceing electron injection from sensitizer to TiO2 following a shift toward pos. potentials of the conduction band of TiO2 by the adsorption of protons or cations from the sensitizer, or from the redox electrolyte and (2) improving the regeneration reaction of the oxidized dye by the redox electrolyte by the dissoln. of aggregated dye from the surface of TiO2 following the treatment.
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| 3. |
- Sjödin, Martin, et al.
(författare)
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Switching the redox mechanism : Models for proton coupled electron transfer from tyrosine and tryptophan
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 127:11, s. 3855-3863
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Tidskriftsartikel (refereegranskat)abstract
- The coupling of electron and proton transfer is an important controlling factor in radical proteins, such as photosystem II, ribinucleotide reductase, cytochrome oxidases, and DNA photolyase. This was investigated in model complexes in which a tyrosine or tryptophan residue was oxidized by a laser-flash generated trisbipyridine-Ru-III moiety in an intramolecular, proton-coupled electron transfer (PCET) reaction. The PCET was found to proceed in a competition between a stepwise reaction, in which electron transfer is followed by deprotonation of the amino acid radical (ETPT), and a concerted reaction, in which both the electron and proton are transferred in a single reaction step (CEP). Moreover, we found that we could analyze the kinetic data for PCET by Marcus' theory for electron transfer. By altering the solution pH, the strength of the Ru-III oxidant, or the identity of the amino acid, we could induce a switch between the two mechanisms and obtain quantitative data for the parameters that control which one will dominate. The characteristic pH-dependence of the CEP rate (M. Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932) reflects the pH-dependence of the driving force caused by proton release to the bulk. For the pH-independent ETPT on the other hand, the driving force of the rate-determining ET step is pH-independent and smaller. On the other hand, temperature-dependent data showed that the reorganization energy was higher for CEP, while the pre-exponential factors showed no significant difference between the mechanisms. Thus, the opposing effect of the differences in driving force and reorganization energy determines which of the mechanisms will dominate. Our results show that a concerted mechanism is in general quite likely and provides a low-barrier reaction pathway for weakly exoergonic reactions. In addition, the kinetic isotope effect was much higher for CEP (k(H)/k(D) > 10) than for ETPT (k(H)/k(D) = 2), consistent with significant changes along the proton reaction coordinate in the rate-determining step of CEP.
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| 4. |
- Sun, S. G., et al.
(författare)
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Studies of a series of novel rhenium(I) bipyridyl dyes for solar cells
- 2005
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Ingår i: Chinese Chemical Letters. - 1001-8417 .- 1878-5964. ; 16:5, s. 677-680
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel rhenium(I) 2,2'-bipyridyl complexes [fac-Re(4,4'-di-COOEt-bpy)-(CO)(3)(Xpy)PF6], where bpy is 2,2'-bipyridine, py is pyridine and X is 3-methyl, 3-hydroxy, or 3-amino, were synthesized, their photophysical and electrochemical properties were studied. The Re(II/I) oxidation potentials decreased as the X group becomes more electron donating from H to 3-methyl, 3-hydroxy, or 3-amino, which might be a very convenient ways for adjusting the electron transfer driving force.
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| 5. |
- Xu, Yunhua, et al.
(författare)
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A New Dinuclear Ruthenium Complex as an Efficient Water Oxidation Catalyst
- 2009
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 48:7, s. 2717-2719
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Tidskriftsartikel (refereegranskat)abstract
- A dinuclear ruthenium complex, which acts as a molecular catalyst for water oxidation, has been synthesized and characterized. The electronic and electrochemical properties were studied by UV-vis spectroscopy and cyclic voltammetry. The oxidation potentials of the complex are significantly lowered by introducing a negatively charged carboxylate ligand, in comparison with those of the reported complexes that have neutral ligands. The catalytic activity of the complex toward water oxidation using Ce(NH4)(2)(NO3)(6) as a chemical oxidant was investigated by means of an oxygen electrode and mass spectrometry. The turnover number of this catalyst with Ce-IV as the chemical oxidant was found to be ca. 1700. The mass spectroscopic analysis of the isotopomer distribution in oxygen evolved from O-18-labeled water indicates that O atoms in the evolved oxygen originate from water.
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| 6. |
- Xu, Y. H., et al.
(författare)
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Synthesis and characterization of dinuclear ruthenium complexes covalently linked to Ru-II tris-bipyridine : An approach to mimics of the donor side of photosystem II
- 2005
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 11:24, s. 7305-7314
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Tidskriftsartikel (refereegranskat)abstract
- To mimic the electron-donor side of photosystem II (PSII), three trinuclear ruthenium complexes (2, 2a, 2b) were synthesized. In these compl plexes, a mixed-valent dinuclear Ru-2(II,III) moiety with one phenoxy and two acetato bridges is covalently linked to a Ru-II tris-bipyridine photosensitizer. The properties and photoinduced electron/energy transfer of these complexes were studied. The results show that the Ru-2(II,III) moieties in the complexes readily undergo reversible one-electron reduction and one-electron oxidation to give the Ru-2(II,II) and Ru-2(II,III) states, respectively. This could allow for photooxidation of the sensitizer part with an external acceptor and subsequent electron transfer from the dinuclear ruthenium moiety to regenerate the sensitizer. However, all trinuclear ruthenium complexes have a very short excited-state lifetime, in the range of a few nanoseconds to less than 100 ps. Studies by femtosecond time-resolved techniques suggest that a mixture of intramolecular energy and electron transfer between the dinuclear ruthenium moiety and the excited [Ru(bpy)(3)](2+) photosensitizer is responsible for the short lifetimes. This problem is overcome by anchoring the complexes with ester- or carboxyl-substituted bipyridine ligands (2a, 2b) to nanocrystalline TiO2, and the desired electron transfer from the excited state of the [Ru(bPY)(3)](2+) moiety to the conduction band of TiO2, followed by intramolecular electron transfer from the dinuclear Ru-2(II,III) moiety to photogenerated Ru-III was observed. The resulting long-lived Ru-2(III,III) state decays on the millisecond timescale.
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| 7. |
- Xu, Yunhua, 1964-
(författare)
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Synthesis and Photoinduced Electron Transfer of Donor-Sensitizer-Acceptor Systems
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Artificial systems involving water oxidation and solar cells are promising ways for the conversion of solar energy into fuels and electricity. These systems usually consist of a photosensitizer, an electron donor and / or an electron acceptor. This thesis deals with the synthesis and photoinduced electron transfer of several donor-sensitizer-acceptor supramolecular systems.The first part of this thesis describes the synthesis and properties of two novel dinuclear ruthenium complexes as electron donors to mimic the donor side reaction of Photosystem II. These two Ru2 complexes were then covalently linked to ruthenium trisbipyridine and the properties of the resulting trinuclear complexes were studied by cyclic voltammetry and transient absorption spectroscopy.The second part presents the synthesis and photoinduced electron transfer of covalently linked donor-sensitizer supramolecular systems in the presence of TiO2 as electron acceptors. Electron donors are tyrosine, phenol and their derivatives, and dinuclear ruthenium complexes. Intramolecular electron transfer from the donor to the oxidized sensitizer was observed by transient absorption spectroscopy after light excitation of the Ru(bpy)32+ moiety. The potential applications of Ru2-based electron donors in artificial systems for water oxidation and solar cells are discussed.In the final part, the photoinduced interfacial electron transfer in the systems based on carotenoids and TiO2 is studied. Carotenoids are shown to act as both sensitizers and electron donors, which could be used in artificial systems to mimic the electron transfer chain in natural photosynthesis.
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| 8. |
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