Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex |
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| Authors: | Dr William Herzog Dr Catherine Bronner Susanne Löffler Dr Bice He Daniel Kratzert Prof Dietmar Stalke Prof Andreas Hauser Prof Oliver S Wenger |
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| Institution: | 1. Département de Chimie Physique, Université de Genève, 30 quai Ernest‐Ansermet, 1211 Genève 4 (Switzerland);2. Departement für Chemie, Universit?t Basel, Spitalstrasse 51, 4056 Basel (Switzerland);3. Institut für Anorganische Chemie, Georg‐August Universit?t, Tammannstrasse 4, 37077 G?ttingen (Germany) |
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| Abstract: | Two pyridylphenols with intramolecular hydrogen bonds between the phenol and pyridine units have been synthesized, characterized crystallographically, and investigated by cyclic voltammetry and UV/Vis spectroscopy. Reductive quenching of the triplet metal‐to‐ligand charge‐transfer excited state of the Re(CO)3(phen)(py)]+ complex (phen=1,10‐phenanthroline, py=pyridine) by the two pyridylphenols and two reference phenol molecules is investigated by steady‐state and time‐resolved luminescence spectroscopy, as well as by transient absorption spectroscopy. Stern–Volmer analysis of the luminescence quenching data provides rate constants for the bimolecular excited‐state quenching reactions. H/D kinetic isotope effects for the pyridylphenols are on the order of 2.0, and the bimolecular quenching reactions are up to 100 times faster with the pyridylphenols than with the reference phenols. This observation is attributed to the markedly less positive oxidation potentials of the pyridylphenols with respect to the reference phenols (≈0.5 V), which in turn is caused by proton coupling of the phenol oxidation process. Transient absorption spectroscopy provides unambiguous evidence for the photogeneration of phenoxyl radicals, that is, the overall photoreaction is clearly a proton‐coupled electron‐transfer process. |
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| Keywords: | electron transfer luminescence photochemistry proton transfer transient absorption |
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