Control of photoinduced energy- and electron-transfer steps in zinc porphyrin-oligothiophene-fullerene linked triads with solvent polarity
Control of photoinduced energy- and electron-transfer steps in zinc porphyrin-oligothiophene-fullerene linked triads with solvent polarity
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DOI：
10.1021/jp044316v
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发表时间：
2005-08-04
影响因子：
3.3
通讯作者：
Otsubo, T
中科院分区：
文献类型：
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作者：
Nakamura, T;Ikemoto, J;Otsubo, T
锌卟啉（ZnP）-低聚噻吩（nT）-富勒烯（C-60）连接的三元组（ZnP-nT-C-60）在溶剂极性下证实了电荷分离（CS）态寿命的巨大变化。选择性激发 ZnP-nT-C60 的 ZnP 部分后，发生从 (ZnP)-Zn-1* 部分到 C-60 部分的能量转移，生成 ZnP-nT-C-1(60)*。在极性溶剂中，CS过程也直接通过(ZnP)-Zn-1*部分发生，生成ZnP.+-nT-C-60(.-)，以及能量转移到C60部分。能量转移后，C-1(60)* 部分发生间接 CS 过程。在极性较小的溶剂苯甲醚中，ZnP.+-nT-C-60(.-)的自由基阳离子（空穴）转移到nT部分；因此，nT部分起到了阳离子捕获剂的作用，并且空穴移动速率被评估为大约10(8) s(-1)；然后，最终的CS状态ZnP-nT(.+)-C-60(.-)持续6-7μs。在中等极性溶剂邻二氯苯(o-DCB)中，ZnP-nT(.+)-C-60(.-)和ZnP.+-nT-C60(.-)以平衡状态存在，因为两种状态具有几乎相同的热力学稳定性。这种平衡导致 o-DCB 中 CS 态的寿命相当长（450-910 μs）。在极性较大的苯甲腈中，ZnP-nT(.+)-C-60(.-)的生成被证实具有明显的短寿命（0.6-0.8μs），这可以通过空穴快速转移到更稳定的ZnP.+-nT-C-60(.-)以及随后更快的电荷重组来解释。结果表明，两个 CS 态能级之间的关系强烈依赖于溶剂极性，导致 ZnP-nT-C60 中 CS 态寿命发生巨大变化；也就是说，最适合长寿命 CS 态的溶剂是中等极性溶剂，例如 o-DCB。与我们之前的 H2P-nT-C-60 数据（其中 H2P 是游离碱卟啉）相比，ZnP-nT-C-60 的 CS 态寿命比 o-DCB 中的 CS 态寿命长 30 倍。
The dramatic changes of the lifetimes of the charge-separated (CS) states were confirmed in zinc porphyrin (ZnP)-oligothiophene (nT)-fullerene (C-60) linked triads (ZnP-nT-C-60) with the solvent polarity. After the selective excitation of the ZnP moiety of ZnP-nT-C60, an energy transfer took place from the (ZnP)-Zn-1* moiety to the C-60 moiety, generating ZnP-nT-C-1(60)*. In polar solvents, the CS process also took place directly via the (ZnP)-Zn-1* moiety, generating ZnP.+-nT-C-60(.-), as well as the energy transfer to the C60 moiety. After this energy transfer, an indirect CS process took place from the C-1(60)* moiety. In the less polar solvent anisole, the radical cation (hole) of ZnP.+-nT-C-60(.-) shifted to the nT moiety; thus, the nT moiety behaves as a cation trapper, and the rates of the hole shift were evaluated to be in the order of 10(8) s(-1); then, the final CS states ZnP-nT(.+)-C-60(.-) were lasting for 6-7 mu s. In the medium polar solvent o-dichlorobenzene (o-DCB), ZnP-nT(.+)-C-60(.-) and ZnP.+-nT-C60(.-) were present as an equilibrium, because both states have almost the same thermodynamic stability. This equilibrium resulted in quite long lifetimes of the CS states (450-910 mu s) in o-DCB. In the more polar benzonitrile, the generation of ZnP-nT(.+)-C-60(.-) was confirmed with apparent short lifetimes (0.6-0.8 mu s), which can be explained by the fast hole shift to more stable ZnP.+-nT-C-60(.-) followed by the faster charge recombination. It was revealed that the relation between the energy levels of two CS states, which strongly depend on the solvent polarity, causes dramatic changes of the lifetimes of the CS states in ZnP-nT-C60; that is, the most appropriate solvents for the long-lived CS state are intermediately polar solvents such as o-DCB. Compared with our previous data for H2P-nT-C-60, in which H2P is free-base porphyrin, the lifetimes of the CS states of ZnP-nT-C-60 are similar to 30 times longer than those in o-DCB.