Ruthenium-manganese complexes for artificial photosynthesis: Factors controlling intramolecular electron transfer and excited-state quenching reactions

Malin L.A. Abrahamsson, Helena Berglund Baudin, Anh Tran, Christian Philouze, Katja E. Berg, Mary Katherine Raymond-Johansson, Licheng Sun, Björn Åkermark, Stenbjörn Styring, Leif Hammarström

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Abstract

Continuing our work toward a system mimicking the electron-transfer steps from manganese to P680+ 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 (kET) values span a large range, 1 × 105-2 × 107 S-1, and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (λ = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically λ ≈ 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.

Original languageEnglish
Pages (from-to)1534-1544
Number of pages11
JournalInorganic Chemistry
Volume41
Issue number6
DOIs
Publication statusPublished - Mar 25 2002

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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    Abrahamsson, M. L. A., Berglund Baudin, H., Tran, A., Philouze, C., Berg, K. E., Raymond-Johansson, M. K., Sun, L., Åkermark, B., Styring, S., & Hammarström, L. (2002). Ruthenium-manganese complexes for artificial photosynthesis: Factors controlling intramolecular electron transfer and excited-state quenching reactions. Inorganic Chemistry, 41(6), 1534-1544. https://doi.org/10.1021/ic0107227