Stepwise Charge Separation and Charge Recombination in Ferrocene-meso,meso-Linked Porphyrin Dimer-Fullerene Triad
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- 作者：Hiroshi Imahori ; Koichi Tamaki ; Yasuyuki Araki ; Yuji Sekiguchi ; Osamu Ito ; Yoshiteru Sakata ; and Shunichi Fukuzumi
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：May 8, 2002
- 年：2002
- 卷：124
- 期：18
- 页码：5165 - 5174
- 全文大小：165K
- 年卷期：v.124,no.18(May 8, 2002)
- ISSN：1520-5126
文摘
A meso,meso-linked porphyrin dimer [(ZnP)2] as a light-harvesting chromophore has beenincorporated into a photosynthetic multistep electron-transfer model for the first time, including ferrocene(Fc), as an electron donor and fullerene (C60) as an electron acceptor to construct the ferrocene-meso,meso-linked porphyrin dimer-fullerene system (Fc-(ZnP)2-C60). Photoirradiation of Fc-(ZnP)2-C60 results inphotoinduced electron transfer from the singlet excited state of the porphyrin dimer [1(ZnP)2*] to the C60moiety to produce the porphyrin dimer radical cation-C60 radical anion pair, Fc-(ZnP)2
+-C60-. Incompetition with the back electron transfer from C60- to (ZnP)2+ to the ground state, an electron transferfrom Fc to (ZnP)2+ occurs to give the final charge-separated (CS) state, that is, Fc+-(ZnP)2-C60-, whichis detected as the transient absorption spectra by the laser flash photolysis. The quantum yield of formationof the final CS state is determined as 0.80 in benzonitrile. The final CS state decays obeying first-orderkinetics with a lifetime of 19 
s in benzonitrile at 295 K. The activation energy for the charge recombination(CR) process is determined as 0.15 eV in benzonitrile, which is much larger than the value expected fromthe direct CR process to the ground state. This value is rather comparable to the energy difference betweenthe initial CS state (Fc-(ZnP)2+-C60-) and the final CS state (Fc+-(ZnP)2-C60-). This indicates that theback electron transfer to the ground state occurs via the reversed stepwise processes,that is, a rate-limitingelectron transfer from (ZnP)2 to Fc+ to give the initial CS state (Fc-(ZnP)2+-C60-), followed by a fastelectron transfer from C60- to (ZnP)2+ to regenerate the ground state, Fc-(ZnP)2-C60. This is in sharpcontrast with the extremely slow direct CR process of bacteriochlorophyll dimer radical cation-quinoneradical anion pair in bacterial reaction centers.
+-C60-. Incompetition with the back electron transfer from C60- to (ZnP)2+ to the ground state, an electron transferfrom Fc to (ZnP)2+ occurs to give the final charge-separated (CS) state, that is, Fc+-(ZnP)2-C60-, whichis detected as the transient absorption spectra by the laser flash photolysis. The quantum yield of formationof the final CS state is determined as 0.80 in benzonitrile. The final CS state decays obeying first-orderkinetics with a lifetime of 19 s in benzonitrile at 295 K. The activation energy for the charge recombination(CR) process is determined as 0.15 eV in benzonitrile, which is much larger than the value expected fromthe direct CR process to the ground state. This value is rather comparable to the energy difference betweenthe initial CS state (Fc-(ZnP)2+-C60-) and the final CS state (Fc+-(ZnP)2-C60-). This indicates that theback electron transfer to the ground state occurs via the reversed stepwise processes,that is, a rate-limitingelectron transfer from (ZnP)2 to Fc+ to give the initial CS state (Fc-(ZnP)2+-C60-), followed by a fastelectron transfer from C60- to (ZnP)2+ to regenerate the ground state, Fc-(ZnP)2-C60. This is in sharpcontrast with the extremely slow direct CR process of bacteriochlorophyll dimer radical cation-quinoneradical anion pair in bacterial reaction centers.