Through-space electronic energy transfer across proximal molecular dyads.
Through-space electronic energy transfer across proximal molecular dyads.
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DOI：
10.1002/anie.201302081
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发表时间：
2013-06
影响因子：
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通讯作者：
A. Harriman;Mohammed A. H. Alamiry;J. Hagon;Delphine Hablot;R. Ziessel
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文献类型：
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作者：
A. Harriman;Mohammed A. H. Alamiry;J. Hagon;Delphine Hablot;R. Ziessel
明确的发色团之间电子能量转移的速率常数 (kEET) 可用作确定所研究系统的结构信息的方法。最显着的例子来自生物化学，其中蛋白质结合的反应物相距 30 或更多，并且仅存在非常弱的电子相互作用。在这种情况下，Fçrster 库仑机制可能成立，多极相互作用可以忽略不计。在某些情况下，反应物对的间隔距离和/或相互取向可以从光谱观察中推断出来。人们通常认为这种理想的偶极子近似会在较短的间隔下崩溃，但这种行为的确凿的实验证据很少。事实上，事实证明，Fçrster 理论至少在某些情况下对 20 次分离的实验 kEET 值给出了可接受的解释，而当反应物具有异常短的跃迁偶极矩向量时，甚至更小的分离也是可能的。研究还表明，所谓的刚性有机框架在环境温度下的流体溶液中会遭受相当大的面外弯曲。如果最低能量构象对各自的跃迁偶极矩向量施加正交性，则这种结构波动可能对观察到的 kEET 值有显着贡献。用于在紧密间隔但弱耦合的反应物之间表达电子能量转移（EET）的替代方案是可用的，但尚未经过分子二元组的充分测试。这些处理方法包括库恩及其同事引入的扩展偶极子方法，其中 Fçrster 理论固有的点偶极子被固定长度的线性偶极子取代。更严格的处理包括原子方法，其中跃迁偶极矩被分解为每个原子的贡献，以及跃迁密度立方体在整个波函数上执行类似的工作。在这里，我们比较了三个精心挑选的分子二联体的实验和计算的 kEET 值，这三个分子二联体的中心连接器的几何形状不同。在每种情况下，供体 (D) 是二酮吡咯并吡咯 (DPP) 染料，而相应的受体 (A) 是带有乙烯基噻吩单元作为共轭延伸剂的延伸硼二吡咯亚甲基 (Bodipy) 染料（方案 1）；看
The rate constant (kEET) for electronic energy transfer between well-defined chromophores can be employed as a means to determine structural information about the system under investigation. The most notable examples arise from biochemistry where protein-bound reactants are separated by 30 or more and where there are only very weak electronic interactions. Under such conditions, the Fçrster coulombic mechanism is likely to hold and multipole interactions can be ignored. In certain cases, the separation distance and/or mutual orientation of the reactant pair can be deduced from spectroscopic observations. It is often considered that this ideal dipole approximation will breakdown at shorter separations but hard experimental evidence for such behavior is scarce. In fact, it has been shown that Fçrster theory gives an acceptable account of experimental kEET values at 20 separations, at least in certain situations, while even smaller separations become possible when the reactants possess unusually short transition dipole moment vectors. It has also been shown that supposedly rigid organic frameworks are subject to considerable out-of-plane bending in fluid solution at ambient temperature. Such structural fluctuations might contribute significantly to the observed kEET values if the lowest-energy conformation imposes orthogonality on the respective transition dipole moment vectors. Alternative protocols for expressing electronic energy transfer (EET) between closely spaced but weakly coupled reactants are available but have not been well-tested with molecular dyads. Such treatments include the extended dipole approach, introduced by Kuhn and co-workers, where the point dipoles inherent to Fçrster theory are replaced with a linear dipole of fixed length. More rigorous treatments include the atomistic approach, where the transition dipole moments are broken down into contributions for each atom, and the transition density cube that does a similar job over the entire wave function. Herein, we compare experimental and computed kEET values for three carefully selected molecular dyads that differ in terms of the geometry of the central connector. In each case, the donor (D) is a diketopyrrolopyrrole (DPP) dye while the corresponding acceptor (A) is an extended boron dipyrromethene (Bodipy) dye fitted with ethenylthiophene units as the conjugation extenders (Scheme 1); see