Imahori H, Tamaki K, Guldi D M, Luo C, Fujitsuka M, Ito O, Sakata Y, Fukuzumi S
Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
J Am Chem Soc. 2001 Mar 21;123(11):2607-17. doi: 10.1021/ja003346i.
Photoinduced charge separation (CS) and charge recombination (CR) processes have been examined in various porphyrin-fullerene linked systems (i.e., dyads and triads) by means of time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. The investigated compounds comprise a homologous series of rigidly linked, linear donor-acceptor arrays with different donor-acceptor separations and diversified donor strength: freebase porphyrin-C60 dyad (H2P-C60), zincporphyrin-C60 dyad (ZnP-C60), ferrocene-zincporphyrin-C60 triad (Fc-ZnP-C60), ferrocene-freebase porphyrin-C60 triad (Fc-H2P-C60), and zincporphyrin-freebase porphyrin-C60 triad (ZnP-H2P-C60). Most importantly, the lowest lying charge-separated state of all the investigated systems, namely, that of ferrocenium ion (Fc+) and the C60 radical anion (C60.-) pair in the Fc-ZnP-C60 triad, has been generated with the highest quantum yields (close to unity) and reveals a lifetime as long as 16 micros. Determination of CS and CR rate constants, together with the one-electron redox potentials of the donor and acceptor moieties in different solvents, has allowed us to examine the driving force dependence (-DeltaG0ET) of the electron-transfer rate constants (kET). Hereby, the semilogarithmic plots (i.e., log kET versus -DeltaG0ET) lead to the evaluation of the reorganization energy (lambda) and the electronic coupling matrix element (V) in light of the Marcus theory of electron-transfer reactions: lambda = 0.66 eV and V = 3.9 cm(-1) for ZnP-C60 dyad and lambda = 1.09 eV and V = 0.019 cm(-1) for Fc-ZnP-C60, Fc-H2P-C60, and ZnP-H2P-C60 triads. Interestingly, the Marcus plot in Fc-ZnP-C60, Fc-H2P-C60, and ZnP-H2P-C60 has provided clear evidence for intramolecular CR located in both the normal and inverted regions of the Marcus parabola. The coefficient for the distance dependence of V (damping factor: betaCR = 0.58 A(-1) is deduced which depends primarily on the nature of the bridging molecule.
通过时间分辨瞬态吸收光谱和荧光寿命测量，已在各种卟啉 - 富勒烯连接体系（即二元体系和三元体系）中研究了光诱导电荷分离（CS）和电荷复合（CR）过程。所研究的化合物包括一系列具有不同供体 - 受体间距和多样化供体强度的刚性连接的线性供体 - 受体阵列：游离碱卟啉 - C60二元体系（H2P - C60）、锌卟啉 - C60二元体系（ZnP - C60）、二茂铁 - 锌卟啉 - C60三元体系（Fc - ZnP - C60）、二茂铁 - 游离碱卟啉 - C60三元体系（Fc - H2P - C60）以及锌卟啉 - 游离碱卟啉 - C60三元体系（ZnP - H2P - C60）。最重要的是，在Fc - ZnP - C60三元体系中，所有研究体系的最低电荷分离态，即二茂铁离子（Fc +）和C60自由基阴离子（C60· -）对，已以最高量子产率（接近1）生成，并且其寿命长达16微秒。通过测定CS和CR速率常数，以及不同溶剂中供体和受体部分的单电子氧化还原电位，我们得以研究电子转移速率常数（kET）对驱动力（-ΔG0ET）的依赖性。据此，根据电子转移反应的马库斯理论，半对数图（即log kET对 -ΔG0ET）可用于评估重组能（λ）和电子耦合矩阵元（V）：对于ZnP - C60二元体系，λ = 0.66 eV且V = 3.9 cm - 1；对于Fc - ZnP - C60、Fc - H2P - C60和ZnP - H2P - C60三元体系，λ = 1.09 eV且V = 0.019 cm - 1。有趣的是，Fc - ZnP - C60、Fc - H2P - C60和ZnP - H2P - C60中的马库斯图为位于马库斯抛物线正常和反转区域的分子内CR提供了明确证据。推导出了V的距离依赖性系数（阻尼因子：βCR = 0.58 Å - 1），它主要取决于桥连分子的性质。
