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Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex
Author(s) -
Herzog William,
Bronner Catherine,
Löffler Susanne,
He Bice,
Kratzert Daniel,
Stalke Dietmar,
Hauser Andreas,
Wenger Oliver S.
Publication year - 2013
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201201069
Subject(s) - chemistry , photochemistry , quenching (fluorescence) , electron transfer , absorption spectroscopy , intramolecular force , pyridine , ultrafast laser spectroscopy , excited state , cyclic voltammetry , proton coupled electron transfer , hydrogen bond , rhenium , spectroscopy , molecule , inorganic chemistry , stereochemistry , fluorescence , organic chemistry , electrochemistry , physics , electrode , quantum mechanics , nuclear physics
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.