Department of Chemistry, University of Rochester, Rochester, New York 14627, USA.
J Am Chem Soc. 2010 Nov 10;132(44):15480-3. doi: 10.1021/ja1057357.
Rhodamine photosensitizers (PSs) substituting S or Se for O in the xanthene ring give turnover numbers (TONs) as high as 9000 for the generation of hydrogen via the reduction of water using [Co(III)(dmgH)(2)(py)Cl] (where dmgH = dimethylglyoximate and py = pyridine) as the catalyst and triethanolamine as the sacrificial electron donor. The turnover frequencies were 0, 1700, and 5500 mol H(2)/mol PS/h for O, S, and Se derivatives, respectively (Φ(H(2)) = 0%, 12.2%, and 32.8%, respectively), which correlates well with relative triplet yields estimated from quantum yields for singlet oxygen generation. Phosphorescence from the excited PS was quenched by the sacrificial electron donor. Fluorescence lifetimes were similar for the O- and S-containing rhodamines (∼2.6 ns) and shorter for the Se analog (∼0.1 ns). These data suggest a reaction pathway involving reductive quenching of the triplet excited state of the PS giving the reduced PS(-) that then transfers an electron to the Co catalyst. The longer-lived triplet state is necessary for effective bimolecular electron transfer. While the cobalt/rhodamine/triethanolamine system gives unprecedented yields of hydrogen for the photoreduction of water, mechanistic insights regarding the overall reaction pathway as well as system degradation offer significant guidance to developing even more stable and efficient photocatalytic systems.
罗丹明类光敏剂（PSs）将氧原子替换为硫或硒原子，可使通过还原水产生氢气的转化率（TON）高达 9000，所用催化剂为[Co(III)(dmgH)(2)(py)Cl]（其中 dmgH = 二甲基乙二肟，py = 吡啶），牺牲电子供体为三乙醇胺。TON 分别为氧、硫和硒衍生物的 0、1700 和 5500 mol H2/mol PS/h（相应的 Φ(H2)分别为 0%、12.2%和 32.8%），这与从单线态氧生成量子产率估算的相对三重态产率很好地相关。受牺牲电子供体的影响，激发 PS 的磷光被猝灭。含氧和硫的罗丹明的荧光寿命相似（约 2.6 ns），而硒类似物的荧光寿命较短（约 0.1 ns）。这些数据表明存在涉及 PS 的三重态激发态还原猝灭的反应途径，从而生成还原 PS(-)，然后将电子转移至 Co 催化剂。长寿命的三重态对于有效的双分子电子转移是必要的。虽然钴/罗丹明/三乙醇胺体系为水的光还原提供了前所未有的氢气产率，但对整个反应途径以及系统降解的机制见解为开发更稳定和高效的光催化体系提供了重要指导。
