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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photoinduced energy and electron-transfer processes in porphyrin - Perylene bisimide symmetric triads
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Photoinduced energy and electron-transfer processes in porphyrin - Perylene bisimide symmetric triads

机译：卟啉-Per双酰亚胺对称三联体中的光诱导能量和电子转移过程

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摘要

The photophysics of two symmetric triads, (ZnP)(2)PBI and (H2P)(2)PBI, made of two zinc or free-base porphyrins covalently attached to a central perylene bisimide unit has been investigated in dichloromethane and in toluene. The solvent has been shown to affect not only quantitatively but also qualitatively the photophysical behavior. A variety of intercomponent processes (singlet energy transfer, triplet energy transfer, photoinduced charge separation, and recombination) have been time-resolved using a combination of emission spectroscopy and femtosecond and nanosecond time-resolved absorption techniques yielding a very detailed picture of the photophysics of these systems. The singlet excited state of the lowest energy chromophore (perylene bisimide in the case of (ZnP)(2)PBI, porphyrin in the case of (H2P)(2)PBI) is always quantitatively populated, besides by direct light absorption, by ultrafast singlet energy transfer (few picosecond time constant) from the higher energy chromophore. In dichloromethane, the lowest excited singlet state is efficiently quenched by electron transfer leading to a charge-separated state where the porphyrin is oxidized and the perylene bisimide is reduced. The systems then go back to the ground state by charge recombination. The four charge separation and recombination processes observed for (ZnP)(2)PBI and (H2P)(2)PBI in dichloromethane take place in the sub-nanosecond time scale. They obey standard free-energy correlations with charge separation lying in the normal regime and charge recombination in the Marcus inverted region. In less polar solvents, such as toluene, the energy of the charge-separated states is substantially lifted leading to sharp changes in photophysical mechanism. With (ZnP)(2)PBI, the electron-transfer quenching is still fast, but charge recombination takes place now in the nanosecond time scale and to triplet state products rather than to the ground state. Triplet-triplet energy transfer from the porphyrin to the perylene bisimide is also involved in the subsequent deactivation of the triplet manifold to the ground state. With (H2P)(2)PBI, on the other hand, the driving force for charge separation is too small for electron-transfer quenching, and the deactivation of the porphyrin excited singlet takes place via intersystem crossing to the triplet followed by triplet energy transfer to the perylene bisimide and final decay to the ground state.
机译：在二氯甲烷和甲苯中研究了由两个锌或游离碱卟啉共价连接到中心central双酰亚胺单元上的两个对称三单元组（ZnP）（2）PBI和（H2P）（2）PBI的光物理性质。已显示溶剂不仅在数量上而且在质量上影响光物理行为。结合发射光谱学和飞秒和纳秒时间分辨吸收技术，已经时间分辨了各种相互间的过程（单能量转移，三重态能量转移，光诱导的电荷分离和重组），从而获得了非常详细的光物理图像。这些系统。能量最低的发色团的单线激发态（对于（ZnP）（2）PBI，为per双酰亚胺;对于（H2P）（2）PBI，为卟啉），除了直接吸收光之外，还通过超快定量地填充高能发色团的单重态能量转移（几皮秒时间常数）。在二氯甲烷中，最低的激发单重态通过电子转移被有效地淬灭，从而导致电荷分离状态，其中卟啉被氧化，the二酰亚胺被还原。然后，系统通过电荷重组回到基态。观察到的（ZnP）（2）PBI和（H2P）（2）PBI在二氯甲烷中的四种电荷分离和重组过程是在亚纳秒级进行的。他们服从标准的自由能相关性，其中电荷分离处于正常状态，而Marcus反向区域中的电荷重组。在极性较小的溶剂（例如甲苯）中，电荷分离态的能量会大大提高，从而导致光物理机制发生急剧变化。使用（ZnP）（2）PBI，电子转移猝灭仍然很快，但现在电荷复合发生在纳秒级的时间范围内，并以三重态产物而不是基态发生。从卟啉到the二酰亚胺的三重态-三重态能量转移也参与了随后的三重态歧管失活至基态。另一方面，对于（H2P）（2）PBI，电荷分离的驱动力对于电子转移猝灭而言太小，并且卟啉激发的单重态的失活是通过与三重态的系统间交叉发生，然后进行三重态能量转移生成bi双酰亚胺，最终衰减至基态。

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