Département de Chimie Physique, Université de Genève, 30 quai Ernest-Ansermet, 1211 Genève 4, Switzerland.
Chemphyschem. 2013 Apr 15;14(6):1168-76. doi: 10.1002/cphc.201201069. Epub 2013 Feb 22.
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.
已经合成了两个具有酚和吡啶单元之间分子内氢键的吡啶基苯酚，并通过循环伏安法和紫外/可见光谱法对其进行了表征和研究。通过稳态和时间分辨发光光谱以及瞬态吸收光谱研究了[Re(CO)3(phen)(py)]+(phen=1,10-菲咯啉，py=吡啶)的三重态金属-配体电荷转移激发态与两个吡啶基苯酚和两个参比苯酚分子的还原猝灭。通过对发光猝灭数据的 Stern-Volmer 分析，提供了双分子激发态猝灭反应的速率常数。吡啶基苯酚的 H/D 动力学同位素效应约为 2.0，与参比苯酚相比，吡啶基苯酚的双分子猝灭反应快了 100 倍。这一观察结果归因于吡啶基苯酚的氧化电位明显比参比苯酚更正（约 0.5 V），这反过来又归因于苯酚氧化过程中的质子偶联。瞬态吸收光谱为酚氧自由基的光生成提供了明确的证据，即总光反应显然是一个质子耦合电子转移过程。
