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Photosynthesis, Artificial: Progress in Swedish Consortium

  1. Sascha Ott,
  2. Stenbjörn Styring,
  3. Leif Hammarström,
  4. Olof Johansson

Published Online: 15 DEC 2011

DOI: 10.1002/9781119951438.eibc0462

Encyclopedia of Inorganic and Bioinorganic Chemistry

Encyclopedia of Inorganic and Bioinorganic Chemistry

How to Cite

Ott, S., Styring, S., Hammarström, L. and Johansson, O. 2011. Photosynthesis, Artificial: Progress in Swedish Consortium. Encyclopedia of Inorganic and Bioinorganic Chemistry. .

Author Information

  1. Uppsala University, Uppsala, Sweden

Publication History

  1. Published Online: 15 DEC 2011

Abstract

Mimicking energy conversion processes in nature using molecular systems is a promising approach for future solar fuel production. The Swedish Consortium for Artificial Photosynthesis is involved in the design, preparation and functional study of many of the key components needed for a homogeneous approach to artificial photosynthesis, building on principles from photosystem II (PSII) and [FeFe] hydrogenases. Ruthenium(II) polypyridyl complexes have played an important role as photosensitizers. Several strategies have been developed for their preparation, and a novel approach to improve the photophysical properties of bistridentate complexes involving six-membered chelates for more octahedral coordination was recently introduced. The [Ru(dqp)2]2+ complexes (dqp is 2,6-di(quinolin-8-yl)pyridine) combine the desired structural properties for easy access to linear donor–acceptor assemblies, while maintaining microsecond luminescent lifetimes of their 3MLCT (metal-to-ligand charge transfer) excited states. The synthesis of these chromophores is now well established, and the recent realization of donor–photosensitizer–acceptor assemblies shows that photoproduced charge-separated states can be formed in high yields (ϕ ≥ 95%). Beyond such single-photon/single-electron events, charge accumulation at potential catalytic sites is crucial for multielectron redox reactions. Covalently linked RuII[BOND]Mnx (x = 1,2) complexes as PSII mimics have been investigated to understand chromophore–quencher (Mn quenchers) interactions, to promote desired electron transfer processes, and suppress undesired competing reactions. The Mn units often have large inner reorganization energies upon oxidation or reduction, which make them unusually slow electron donors and/or acceptors in photoinduced charge-separation schemes. Charge accumulation and water splitting, however, require the management of both protons and electrons, which controls the electron transfer processes by proton-coupled electron transfer (PCET). Studies on RuII[BOND]Tyr complexes incorporating pendant bases led to an understanding of the effect of hydrogen-bonding on electron transfer rates. In analogy to the electron donor side, bioinorganic models of the [FeFe] H2ase active site are targeted for the electron acceptor side, with the ultimate goal to realize molecular catalysts that produce H2 at similar high rates and low overpotential as the enzymes. Certain ligand sets create basic sites around the Fe centers that are protonated in the presence of acid and are thus models of late intermediates in the enzymatic catalytic cycle. Furthermore, synthetic Fe2 complexes catalyze the electrochemical reduction of protons. In combination with a photosensitizer, they can also be used in photochemical schemes and are currently used to produce H2 photochemically, with turnover rates up to 200.

Keywords:

  • biomimetic chemistry;
  • water oxidation;
  • hydrogen production;
  • ruthenium polypyridine;
  • PSII;
  • hydrogenase;
  • electron transfer;
  • donor–acceptor