Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
J Phys Chem A. 2010 Apr 1;114(12):4156-62. doi: 10.1021/jp9119342.
In the present study, photoinduced electron transfer (ET) processes of supramolecular donor-acceptor dyads of Zn 2,3,7,8,11,12,17,18-octaethylhemiporphycene (ZnHPc) and axial ligands were investigated by using various spectroscopic methods. The formation of 1:1 dyads was confirmed by absorption spectral change during titration of axial ligand. The association constants were determined from the spectral change. Quenching of the fluorescence intensity was observed when electron acceptor ability of the axial ligand increased. The driving forces for ET were estimated based on the estimated redox potentials and structural parameters. It became clear that various ZnHPc dyads showed ET because of slightly higher donor-ability and larger excitation energy of ZnHPc when compared to the corresponding dyads of Zn porphycene (ZnPcn). The transient absorption spectra during the sub-picosecond laser flash photolysis showed the formation of charge separated state, that is, radical cation of ZnHPc and radical anion of axial ligand, from the singlet excited ZnHPc. The observed ET rates were compared with the previously reported values for Zn porphyrins and ZnPcn. The ET rates of ZnHPc were located between those observed with porphyrins and ZnPcn supramolecular dyads, even when the -DeltaG values were similar to each other. This observation was explained on the basis of the variation in reorganization energy and electronic coupling (V) values. Furthermore, distribution of HOMO electron density gave a plausible explanation for the variation in V values of these dyads.
在本研究中，通过各种光谱方法研究了锌 2,3,7,8,11,12,17,18-辛基半卟啉（ZnHPc）和轴向配体的超分子给体-受体二聚体的光诱导电子转移（ET）过程。通过滴定轴向配体时吸收光谱的变化证实了 1:1 二聚体的形成。从光谱变化确定了结合常数。当轴向配体的电子接受能力增加时，观察到荧光强度猝灭。根据估计的氧化还原电位和结构参数估算了 ET 的驱动力。清楚的是，与相应的锌卟啉（ZnPcn）二聚体相比，各种 ZnHPc 二聚体由于稍高的给体能力和较大的 ZnHPc 的激发能而显示出 ET。在亚皮秒激光闪光光解期间的瞬态吸收光谱表明，从 ZnHPc 的单重激发态形成了电荷分离态，即 ZnHPc 的自由基阳离子和轴向配体的自由基阴离子。观察到的 ET 速率与先前报道的锌卟啉和 ZnPcn 的值进行了比较。即使 -DeltaG 值彼此相似，ZnHPc 的 ET 速率也位于观察到的卟啉和 ZnPcn 超分子二聚体之间。这种观察结果基于重组能和电子耦合（V）值的变化进行了解释。此外，HOMO 电子密度的分布为这些二聚体的 V 值的变化提供了合理的解释。
