Ultrafast Photoinduced Electron Transfer in Directly Linked Porphyrin-Ferrocene Dyads

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• 作者：Minoru Kubo ; Yukie Mori ; Masana Otani ; Masataka Murakami ; Yukihide Ishibashi ; Masakazu Yasuda ; Kohei Hosomizu ; Hiroshi Miyasaka ; Hiroshi Imahori ; Satoru Nakashima
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：June 21, 2007
• 年：2007
• 卷：111
• 期：24
• 页码：5136 - 5143
• 全文大小：253K
• 年卷期：v.111,no.24(June 21, 2007)
• ISSN：1520-5215

文摘

The ultrafast electron transfer occurring upon Soret excitation of three new porphyrin-ferrocene (XP-Fc)dyads has been studied by femtosecond up-conversion and pump-probe techniques. In the XP-Fc dyads(XP-Fcs) designed in this study, the ferrocene moiety is covalently bonded to the meso positions of 3,5-di-tert-butylphenyl zinc porphyrin (BPZnP-Fc), pentafluorophenyl zinc porphyrin (FPZnP-Fc), and 3,5-di-tert-butylphenyl free-base porphyrin (BPH₂P-Fc). Charge separation and recombination in the XP-Fcswere confirmed by transient absorption spectra, and the lifetimes of the charge-separated states were estimatedfrom the decay rate of the porphyrin radical anion band to be approximately 20 ps. The charge-separationrates of the XP-Fcs were found to be >10¹³ s^-1 from the S₂ state and 6.3 × 10¹² s^-1 from the S₁ state.Charge separation from the S₂ state was particularly efficient for BPZnP-Fc, whereas the main reactionpathway was from the S₁ state for BPH₂P-Fc. Charge separation from the S₂ and S₁ states occurred at virtuallythe same rate in benzene and tetrahydrofuran and was much faster than their solvation times. Analysis ofthese results using semiquantum Marcus theory indicates that the magnitude of the electronic-tunneling matrixelement is rather large and far outside the range of nonadiabatic approximation. The pump-probe data showthe presence of vibrational coherence during the reactions, suggesting that wavepacket dynamics on the adiabaticpotential energy surface might regulate the ultrafast reactions.