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Issue 8, 2012
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Photoinduced electron transfer in covalent ruthenium–anthraquinone dyads: relative importance of driving-force, solvent polarity, and donor–bridge energy gap

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Abstract

Four rigid rod-like molecules comprised of a Ru(bpy)32+ (bpy = 2,2′-bipyridine) photosensitizer, a 9,10-anthraquinone electron acceptor, and a molecular bridge connecting the two redox partners were synthesized and investigated by optical spectroscopic and electrochemical means. An attempt was made to assess the relative importance of driving-force, solvent polarity, and bridge variation on the rates of photoinduced electron transfer in these molecules. Expectedly, introduction of tert-butyl substituents in the bipyridine ligands of the ruthenium complex and a change in solvent from dichloromethane to acetonitrile lead to a significant acceleration of charge transfer rates. In dichloromethane, photoinduced electron transfer is not competitive with the inherent excited-state deactivation processes of the photosensitizer. In acetonitrile, an increase in driving-force by 0.2 eV through attachment of tert-butyl substituents to the bpy ancillary ligands causes an increase in electron transfer rates by an order of magnitude. Replacement of a p-xylene bridge by a p-dimethoxybenzene spacer entails an acceleration of charge transfer rates by a factor of 3.5. In the dyads from this study, the relative order of importance of individual influences on electron transfer rates is therefore as follows: solvent polarity ≥ driving-force > donor–bridge energy gap.

Graphical abstract: Photoinduced electron transfer in covalent ruthenium–anthraquinone dyads: relative importance of driving-force, solvent polarity, and donor–bridge energy gap

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Article information


Submitted
14 Oct 2011
Accepted
13 Dec 2011
First published
19 Jan 2012

Phys. Chem. Chem. Phys., 2012,14, 2685-2692
Article type
Paper

Photoinduced electron transfer in covalent ruthenium–anthraquinone dyads: relative importance of driving-force, solvent polarity, and donor–bridge energy gap

J. Hankache and O. S. Wenger, Phys. Chem. Chem. Phys., 2012, 14, 2685
DOI: 10.1039/C2CP23240E

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