Direct probing of photoinduced electron transfer in a self- assembled biomimetic [2Fe2S]-hydrogenase complex using ultrafast vibrational spectroscopy

Li, P., Amirjalayer, S., Hartl, F. ORCID: https://orcid.org/0000-0002-7013-5360, Lutz, M., de Bruin, B., Becker, R., Woutersen, S. and Reek, J. N. H. (2014) Direct probing of photoinduced electron transfer in a self- assembled biomimetic [2Fe2S]-hydrogenase complex using ultrafast vibrational spectroscopy. Inorganic Chemistry, 53 (10). pp. 5373-5383. ISSN 0020-1669 doi: 10.1021/ic500777d

Abstract/Summary

A pyridyl-functionalized diiron dithiolate complex, [μ-(4-pyCH2−NMI-S2)Fe2(CO)6] (3, py = pyridine(ligand), NMI = naphthalene monoimide) was synthesized and fully characterized. In the presence of zinc tetraphenylporphyrin (ZnTPP), a self-assembled 3·ZnTPP complex was readily formed in CH2Cl2 by the coordination of the pyridyl nitrogen to the porphyrin zinc center. Ultrafast photoinduced electron transfer from excited ZnTPP to complex 3 in the supramolecular assembly was observed in real time by monitoring the ν(CO) and ν(CO)NMI spectral changes with femtosecond time-resolved infrared (TRIR) spectroscopy. We have confirmed that photoinduced charge separation produced the monoreduced species by comparing the time-resolved IR spectra with the conventional IR spectra of 3•− generated by reversible electrochemical reduction. The lifetimes for the charge separation and charge recombination processes were found to be τCS = 40 ± 3 ps and τCR = 205 ± 14 ps, respectively. The charge recombination is much slower than that in an analogous covalent complex, demonstrating the potential of a supramolecular approach to extend the lifetime of the chargeseparated state in photocatalytic complexes. The observed vibrational frequency shifts provide a very sensitive probe of the delocalization of the electron-spin density over the different parts of the Fe2S2 complex. The TR and spectro-electrochemical IR spectra, electron paramagnetic resonance spectra, and density functional theory calculations all show that the spin density in 3•− is delocalized over the diiron core and the NMI bridge. This delocalization explains why the complex exhibits low catalytic dihydrogen production even though it features a very efficient photoinduced electron transfer. The ultrafast porphyrin-to-NMIS2−Fe2(CO)6 photoinduced electron transfer is the first reported example of a supramolecular Fe2S2-hydrogenase model studied by femtosecond TRIR spectroscopy. Our results show that TRIR spectroscopy is a powerful tool to investigate photoinduced electron transfer in potential dihydrogen-producing catalytic complexes, and that way to optimize their performance by rational approaches.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/37100
Identification Number/DOI	10.1021/ic500777d
Refereed	Yes
Divisions	Interdisciplinary centres and themes > Chemical Analysis Facility (CAF) Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
Publisher	American Chemical Society
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