Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17-19, 44121 Ferrara, Italy.
Chemistry. 2013 Jul 8;19(28):9261-71. doi: 10.1002/chem.201300133. Epub 2013 Jun 3.
A noble-metal-free system for photochemical hydrogen production is described, based on ascorbic acid as sacrificial donor, aluminium pyridyl porphyrin as photosensitizer, and cobaloxime as catalyst. Although the aluminium porphyrin platform has docking sites for both the sacrificial donor and the catalyst, the resulting associated species are essentially inactive because of fast unimolecular reversible electron-transfer quenching. Rather, the photochemically active species is the fraction of sensitizer present, in the aqueous/organic solvent used for hydrogen evolution, as free species. As shown by nanosecond laser flash photolysis experiments, its long-lived triplet state reacts bimolecularly with the ascorbate donor, and the reduced sensitizer thus formed, subsequently reacts with the cobaloxime catalyst, thereby triggering the hydrogen evolution process. The performance is good, particularly in terms of turnover frequencies (TOF=10.8 or 3.6 min(-1), relative to the sensitizer or the catalyst, respectively) and the quantum yield (Φ=4.6%, that is, 9.2% of maximum possible value). At high sacrificial donor concentration, the maximum turnover number (TON=352 or 117, relative to the sensitizer or the catalyst, respectively) is eventually limited by hydrogenation of both sensitizer (chlorin formation) and catalyst.
描述了一种基于抗坏血酸作为牺牲供体、铝吡啶卟啉作为光敏剂和钴卟啉作为催化剂的光化学制氢的无贵金属体系。尽管铝卟啉平台具有牺牲供体和催化剂的结合位点，但由于快速的单分子可逆电子转移猝灭，形成的配合物基本上是无活性的。相反，光化学活性物质是在用于制氢的水/有机溶剂中以游离形式存在的敏化剂的一部分。如纳秒激光闪光光解实验所示，其长寿命三重态与抗坏血酸供体发生双分子反应，形成的还原敏化剂随后与钴卟啉催化剂反应，从而引发制氢过程。性能良好，特别是在周转率（TOF=10.8 或 3.6 min(-1)，相对于敏化剂或催化剂）和量子产率（Φ=4.6%，即最大可能值的 9.2%）方面。在高牺牲供体浓度下，最大周转率（TON=352 或 117，相对于敏化剂或催化剂）最终受到敏化剂（氯形成）和催化剂加氢的限制。
