Intramolecular Electron Transfer Reactions Observed for Dawson-Type Polyoxometalates Covalently Linked to Porphyrin Residues
Intramolecular Electron Transfer Reactions Observed for Dawson-Type Polyoxometalates Covalently Linked to Porphyrin Residues
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DOI：
10.1021/jp900643m
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发表时间：
2009-04-09
影响因子：
3.7
通讯作者：
Odobel, Fabrice
中科院分区：
文献类型：
--
作者：
Harriman, Anthony;Elliott, Kristopher J.;Odobel, Fabrice
三个光活性，多组分超分子已被合成和表征，其中卟啉单元共价连接到道森型杂多磷钨酸盐（POM）。这种连接是通过Huisgen反应进行的，该反应在所有情况下都能得到良好的产率，并经过修饰以提供内部灵活性程度不同的连接。来自卟啉单元的荧光被附加的POM猝灭，其效率随着连接体的柔性增加而增加。除了最严格的连接，荧光衰减曲线是非指数的，并解释在多个家庭的构象，不同的能力进行光诱导的电子转移。基态构象的分布进行了检查，通过高压发射光谱。循环伏安法和光谱电化学研究提供了热力学驱动力的定量数据和氧化还原产物的光谱数据。在所有情况下，卟啉上的第一激发单重态能够将电子转移到POM。卟啉的相应三重态的电子转移速率非常慢。在三乙醇胺存在下，作为牺牲电子供体的卟啉的光解导致卟啉π-自由基阴离子的形成。后一种物质能够还原POM，但反应速率非常慢。在这里，双分子电子转移与分子内途径有效竞争，证实了三唑接头是电子的不良导管。在这些条件下，不可能使POM负载多于一个电子。POM的单电子还原形式将电子转移到卟啉的单重激发态，从而形成相对长寿命的电荷移位态。
Three photoactive, multicomponent supermolecules have been synthesized and characterized whereby a porphyrin unit is covalently linked to a Dawson-type heteropolyphosphotungstate (POM). The connection has been made via a Huisgen reaction, which gives good yields in all cases, and modified to provide linkages that vary in their degree of internal flexibility. Fluorescence from the porphyrin unit is quenched by the appended POM, for which the efficiency increases with increasing flexibility of the linker. Except for the most rigid connection, fluorescence decay profiles are nonexponential and are interpreted in terms of multiple families of conformers that differ in their ability to undergo light-induced electron transfer. The distribution of ground-state conformers was examined by high-pressure emission spectroscopy. Cyclic voltammetry and spectro-electrochemical studies provide quantitative data for the thermodynamic driving forces and spectral data for the redox products. In all cases, the first-excited singlet state resident on the porphyrin is capable of transferring an electron to the POM. The rate of electron transfer is very slow for the corresponding triplet state of the porphyrin. Photolysis of the porphyrin in the presence of triethanolamine, present as a sacrificial electron donor, leads to formation of the porphyrin pi-radical anion. This latter species is able to reduce the POM, but the rate of reaction is remarkably slow. Here, bimolecular electron transfer competes effectively with the intramolecular route, confirming that the triazole linker is a poor conduit for electrons. It was not possible, under these conditions, to load the POM with more than a single electron. The one-electron reduced form of the POM transfers an electron to the singlet-excited-state of the porphyrin so as to form a relatively long-lived charge-shift state.