In 1997 we published the first compounds where a manganese electron donor was linked to a photosensitizer Ru-complex. We showed that the photooxidized Ru-complex was regenerated by electron transfer from manganese. We learned about the factors that control both this desired electron transfer and the unproductive quenching reactions. We have showed that at least three electrons can be taken from manganese by light oxidation of the appended Ru-complex. This is close to the four electrons needed for water oxidation. It is a rare example of accumulative light-induced electron transfer in a synthetic system, and mimics the proton-coupled oxidation of the CaMn4 cluster of Photosystem II (see below). We are currently attempting complete photochemical water oxidation with different molecular catalysts.
R. Lomoth et al. Photosynthesis Research (2006) 87, 25-40;
Leif Hammarström and Stenbjörn Styring, Phil. Trans. B, (2008) 363, 1283-1291;
Ann Magnuson et al. Acc. Chem. Res. (2009) 42, 1899-1909.
A Ru-complex with a manganese donor and two naphthalene diimide acceptors showing very long-lived charge separation. Our analysis showed that the unusually slow recombination is due to a high inner reorganization energy of the manganese complex. M. Borgström et al. J. Am. Chem. Soc. (2005), 127, 17504-17515.