Selective triplet-state formation during charge recombination in a fullerene/Bodipy molecular dyad (Bodipy=borondipyrromethene).
Selective triplet-state formation during charge recombination in a fullerene/Bodipy molecular dyad (Bodipy=borondipyrromethene).
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DOI：
10.1002/chem.200900440
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发表时间：
2009-07
期刊：
影响因子：
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通讯作者：
R. Ziessel;Ben D. Allen;D. B. Rewinska;A. Harriman
中科院分区：
文献类型：
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作者：
R. Ziessel;Ben D. Allen;D. B. Rewinska;A. Harriman
合成了一种构象受限的分子二元体，并对其进行了详细的物理化学研究。二联体包含共价连接到巴克敏斯特富勒烯C60残基的硼二吡咯亚甲基（Bodipy）染料，并且在硼中心配备有十六炔单元以辅助溶解性。该连接由二苯基二苯乙炔组成，连接在Bodipy核心的内消旋位置，并通过C60表面的N-甲基吡咯烷环连接。位于两端的三重态基本上是等能的。循环伏安法表明，光诱导的电子转移从Bodipy到C60是化学上有利的，可以竞争在同一方向上的分子内能量转移。光诱导电子提取Bodipy的C60的单重激发态的驱动力取决于溶剂的极性。因此，在非极性溶剂中，光诱导的电子转移是缓慢的上坡，但快速的激发能量转移发生从Bodipy到C60，然后是系统间交叉和随后的两个三重激发态的平衡。移动到极性溶剂开关光诱导电子转移。现在，在苯甲腈中，电荷转移态（CTS）位于三重态能级之下，这样电荷复合就恢复了基态。然而，在CH 2Cl 2或甲基四氢呋喃中，CTS的能量略高于三重态能级，并且部分衰变以形成位于C60残基上的三重态。该步骤是高度特异性的，并且不会导致直接形成位于Bodipy单元上的三重激发态。随后的两个三联体的平衡发生在相对缓慢的时间尺度上。
A conformationally restricted molecular dyad has been synthesized and subjected to detailed photophysical examination. The dyad comprises a borondipyrromethene (Bodipy) dye covalently linked to a buckminsterfullerene C60 residue, and is equipped with hexadecyne units at the boron centre in order to assist solubility. The linkage consists of a diphenyltolane, attached at the meso position of the Bodipy core and through an N-methylpyrrolidine ring at the C60 surface. Triplet states localised on the two terminals are essentially isoenergetic. Cyclic voltammetry indicates that light-induced electron transfer from Bodipy to C60 is thermodynamically favourable and could compete with intramolecular energy transfer in the same direction. The driving force for light-induced electron abstraction from Bodipy by the singlet excited state of C60 depends critically on the solvent polarity. Thus, in non-polar solvents, light-induced electron transfer is thermodynamically uphill, but fast excitation energy transfer occurs from Bodipy to C60 and is followed by intersystem crossing and subsequent equilibration of the two triplet excited states. Moving to a polar solvent switches on light-induced electron transfer. Now, in benzonitrile, the charge-transfer state (CTS) is positioned slightly below the triplet levels, such that charge recombination restores the ground state. However, in CH2Cl2 or methyltetrahydrofuran, the CTS is slightly higher in energy than the triplet levels, and decays, in part, to form the triplet state localized on the C60 residue. This step is highly specific and does not result in direct formation of the triplet excited state localized on the Bodipy unit. Subsequent equilibration of the two triplets takes place on a relatively slow timescale.