Two pyridylphenols with intramolecular hydrogen bonds between the phenol and pyridine units were synthesized, characterized crystallographically, and investigated by cyclic voltammetry and UVvis spectroscopy. Reductive quenching of the 3 MLCT excited state of the [Re(phen)(CO)3(py)]+ complex (phen = 1,10-phenanthroline, py = pyridine) by the two pyridylphenols and two reference phenol molecules was 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 (KIEs) 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 (ca. 0.5 V), which in turn is caused by protoncoupling of the phenol oxidation process. Transient absorption spectroscopy provides unambiguous evidence for the photogeneration of phenoxyl radicals, i. e., the overall photoreaction is clearly a PCET process

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