Effects of metal ions on photoinduced electron transfer in zinc porphyrin-naphthalenediimide linked systems.
Effects of metal ions on photoinduced electron transfer in zinc porphyrin-naphthalenediimide linked systems.
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DOI：
10.1002/chem.200305239
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发表时间：
2004-01
期刊：
影响因子：
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通讯作者：
K. Okamoto;Y. Mori;H. Yamada;H. Imahori;S. Fukuzumi
中科院分区：
文献类型：
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作者：
K. Okamoto;Y. Mori;H. Yamada;H. Imahori;S. Fukuzumi
采用锌卟啉-萘二酰亚胺（ZnP-NIm）二元体系和锌卟啉-均苯四甲酸二酰亚胺-萘二酰亚胺（ZnP-Im-NIm）三元体系研究了金属离子（三氟甲磺酸钪（Sc（OTf）（3））和三氟甲磺酸镥（Lu（OTf）（3））存在下，金属离子对光诱导电荷分离（CS）和电荷复合（CR）过程的影响。通过ZnP（.）（+）和NIm（.）(-)在不存在金属离子和由于ZnP（.）（+）和NIm（.）(-)本文研究了Sc（3+）存在时，Sc（3+）/Sc（3+）配合物的二价体和三价体的时间分辨瞬态吸收光谱。存在1.0 x 10（-3）M Sc（3+）时，电荷分离态的寿命（ZnP-NIm为14微米，ZnP-Im-NIm为8.3微米）比不存在金属离子时的寿命（ZnP-NIm为1.3微米，ZnP-Im-NIm为0.33微米）长十倍以上。与此相反，CS步骤的荧光寿命测量所确定的速率常数是相同的，无论存在或不存在的金属离子。这表明，在Sc（3+）存在下，从（1）ZnP（*）到NIm的光诱导电子转移在没有金属离子参与的情况下发生，以产生ZnP（.）（+）-NIm（.）(-)然后与Sc（3+）络合得到ZnP（.）（+）-NIm（.）(-)/Sc（3+）配合物。在金属离子存在下，NIm部分的单电子还原电位（E（红色））随着金属离子浓度的增加而在正方向上移动，遵守能斯特方程，而ZnP部分的单电子氧化电位保持不变。CS和CR过程中所观察到的速率常数（k（ET））的驱动力依赖性的情况下，在金属离子的存在下，以及在电子转移的Marcus理论的评价。在存在金属离子的情况下，CS过程的驱动力与不存在金属离子的情况下的驱动力相同，而CR过程的驱动力随着金属离子浓度的增加而减小。当CR速率常数变得与金属离子浓度无关时，CR过程的重组能也随着金属离子浓度的增加而减小。
Zinc porphyrin-naphthalenediimide (ZnP-NIm) dyads and zinc porphyrin-pyromellitdiimide-naphthalenediimide (ZnP-Im-NIm) triad have been employed to examine the effects of metal ions on photoinduced charge-separation (CS) and charge-recombination (CR) processes in the presence of metal ions (scandium triflate (Sc(OTf)(3)) or lutetium triflate (Lu(OTf)(3)), both of which can bind with the radical anion of NIm). Formation of the charge-separated states in the absence and in the presence of Sc(3+) was confirmed by the appearance of absorption bands due to ZnP(.) (+) and NIm(.) (-) in the absence of metal ions and of those due to ZnP(.) (+) and the NIm(.) (-)/Sc(3+) complex in the presence of Sc(3+) in the time-resolved transient absorption spectra of dyads and triad. The lifetimes of the charge-separated states in the presence of 1.0 x 10(-3) M Sc(3+) (14 micros for ZnP-NIm, 8.3 micros for ZnP-Im-NIm) are more than ten times longer than those in the absence of metal ions (1.3 micros for ZnP-NIm, 0.33 micros for ZnP-Im-NIm). In contrast, the rate constants of the CS step determined by the fluorescence lifetime measurements are the same, irrespective of the presence or absence of metal ions. This indicates that photoinduced electron transfer from (1)ZnP(*) to NIm in the presence of Sc(3+) occurs without involvement of the metal ion to produce ZnP(.) (+)-NIm(.) (-), followed by complexation with Sc(3+) to afford the ZnP(.) (+)-NIm(.) (-)/Sc(3+) complex. The one-electron reduction potential (E(red)) of the NIm moiety in the presence of a metal ion is shifted in a positive direction with increasing metal ion concentration, obeying the Nernst equation, whereas the one-electron oxidation potential of the ZnP moiety remains the same. The driving force dependence of the observed rate constants (k(ET)) of CS and CR processes in the absence and in the presence of metal ions is well evaluated in terms of the Marcus theory of electron transfer. In the presence of metal ions, the driving force of the CS process is the same as that in the absence of metal ions, whereas the driving force of the CR process decreases with increasing metal ion concentration. The reorganization energy of the CR process also decreases with increasing metal ion concentration, when the CR rate constant becomes independent of the metal ion concentration.