Modulating Charge Separation and Charge Recombination Dynamics in Porphyrin-Fullerene Linked Dyads and Triads: Marcus-Normal versus Inverted Region
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- 作者：Hiroshi Imahori ; Koichi Tamaki ; Dirk M. Guldi ; Chuping Luo ; Mamoru Fujitsuka ; Osamu Ito ; Yoshiteru Sakata ; and Shunichi Fukuzumi
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：March 21, 2001
- 年：2001
- 卷：123
- 期：11
- 页码：2607 - 2617
- 全文大小：164K
- 年卷期：v.123,no.11(March 21, 2001)
- ISSN：1520-5126
文摘
Photoinduced charge separation (CS) and charge recombination (CR) processes have been examinedin various porphyrin-fullerene linked systems (i.e., dyads and triads) by means of time-resolved transientabsorption spectroscopy and fluorescence lifetime measurements. The investigated compounds comprise ahomologous series of rigidly linked, linear donor-acceptor arrays with different donor-acceptor separationsand 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), andzincporphyrin-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) andreveals a lifetime as long as 16 
s. Determination of CS and CR rate constants, together with the one-electronredox potentials of the donor and acceptor moieties in different solvents, has allowed us to examine the drivingforce dependence (-
G0ET) of the electron-transfer rate constants (kET). Hereby, the semilogarithmic plots(i.e., log kET versus -G0ET) lead to the evaluation of the reorganization energy (
) and the electronic couplingmatrix element (V) in light of the Marcus theory of electron-transfer reactions: = 0.66 eV and V = 3.9cm-1 for ZnP-C60 dyad and = 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 clearevidence for intramolecular CR located in both the normal and inverted regions of the Marcus parabola. Thecoefficient for the distance dependence of V (damping factor: 
CR = 0.58 Å-1) is deduced which dependsprimarily on the nature of the bridging molecule.
-) pair in the Fc-ZnP-C60 triad, has been generated with the highest quantum yields (close to unity) andreveals a lifetime as long as 16 s. Determination of CS and CR rate constants, together with the one-electronredox potentials of the donor and acceptor moieties in different solvents, has allowed us to examine the drivingforce dependence (-G0ET) of the electron-transfer rate constants (kET). Hereby, the semilogarithmic plots(i.e., log kET versus -G0ET) lead to the evaluation of the reorganization energy () and the electronic couplingmatrix element (V) in light of the Marcus theory of electron-transfer reactions: = 0.66 eV and V = 3.9cm-1 for ZnP-C60 dyad and = 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 clearevidence for intramolecular CR located in both the normal and inverted regions of the Marcus parabola. Thecoefficient for the distance dependence of V (damping factor: CR = 0.58 Å-1) is deduced which dependsprimarily on the nature of the bridging molecule.