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Ruthenium-Manganese Complexes for Artificial Photosynthesis: Factors Controlling Intramolecular Electron Transfer and Excited State Quenching Reactions
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
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2002 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 41, no 6, 1534-1544 p.Article in journal (Refereed) Published
Abstract [en]

Continuing our work toward a system mimicking the electron-transfer steps from manganese to P(680)(+) in photosystem II (PS II), we report a series of ruthenium(II)-manganese(II) complexes that display intramolecular electron transfer from manganese(II) to photooxidized ruthenium(III). The electron-transfer rate constant (k(ET)) values span a large range, 1 x 10(5)-2 x 10(7) s(-1), and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (lambda = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically lambda approximately 1.0 eV). This result indicates that the inner reorganization energy is relatively large and, consequently, that at moderate driving force values manganese complexes are not fast donors. Both the type of manganese ligand and the link between the two metals are shown to be of great importance to the electron-transfer rate. In contrast, we show that the quenching of the excited state of the ruthenium(II) moiety by manganese(II) in this series of complexes mainly depends on the distance between the metals. However, by synthetically modifying the sensitizer so that the lowest metal-to-ligand charge transfer state was localized on the nonbridging ruthenium(II) ligands, we could reduce the quenching rate constant in one complex by a factor of 700 without changing the bridging ligand. Still, the manganese(II)-ruthenium(III) electron-transfer rate constant was not reduced. Consequently, the modification resulted in a complex with very favorable properties.

Place, publisher, year, edition, pages
2002. Vol. 41, no 6, 1534-1544 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-89491DOI: 10.1021/ic0107227PubMedID: 11896722OAI: oai:DiVA.org:uu-89491DiVA: diva2:161005
Available from: 2001-10-19 Created: 2001-10-19 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Electron Transfer in Ruthenium-Manganese Complexes for Artificial Photosynthesis: Studies in Solution and on Electrode Surfaces
Open this publication in new window or tab >>Electron Transfer in Ruthenium-Manganese Complexes for Artificial Photosynthesis: Studies in Solution and on Electrode Surfaces
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In today’s society there is an increasing need for energy, an increase which for the most part is supplied by the use of fossil fuels. Fossil fuel resources are limited and their use has harmful effects on the environment, therefore the development of technologies that produce clean energy sources is very appealing. Natural photosynthesis is capable of converting solar energy into chemical energy through a series of efficient energy and electron transfer reactions with water as the only electron source. Thus, constructing an artificial system that uses the same principles to convert sunlight into electricity or storable fuels like hydrogen is one of the major forces driving artificial photosynthesis research.

This thesis describes supramolecular complexes with the intention of mimicking the electron transfer reactions of the donor side in Photosystem II, where a manganese cluster together with a tyrosine catalyses the oxidation of water. All complexes are based on Ru(II)-trisbipyridine as a photosensitizer that is covalently linked to electron donors like tyrosine or manganese. Photochemical reactions are studied with time-resolved transient absorption and emission measurements. Electrochemical techniques are used to study the electrochemical behavior, and different photoelectrochemical techniques are used to investigate the complexes adsorbed onto titanium dioxide surfaces. In all complexes, intramolecular electron transfer occurs from the linked donor to photo-oxidized Ru(III). It is also observed that coordinated Mn(II) quenches the excited state of Ru(II), a reaction that is found to be distance dependent. However, by modifying one of the complexes, its excited state properties can be tuned in a way that decreases the quenching and keeps the electron transfer properties. The obtained results are of significance for the development of multinuclear Ru-Mn complexes that are capable of multi-electron transfer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2001. 69 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 669
Keyword
Physics, Artificial photosynthesis, electron transfer, energy transfer, ruthenium, manganese, titanium dioxide, Fysik
National Category
Physical Sciences
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-1468 (URN)91-554-5154-3 (ISBN)
Public defence
2001-11-09, The Svedberg Lecture Hall, Institute of Chemistry, Uppsala University, Uppsala, 10:15
Opponent
Available from: 2001-10-19 Created: 2001-10-19Bibliographically approved

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Hammarström, Leif

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