Electron Transfer at Electrodes through Conjugated "Molecular Wire" Bridges

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• 作者：Stephen Creager ; C. J. Yu ; Cindy Bamdad ; Steve O'Connor ; Tanya MacLean ; Eric Lam ; Yoochul Chong ; Gary T. Olsen ; Jiye Luo ; Michael Gozin ; and Jon Faiz Kayyem
• 刊名：Journal of the American Chemical Society
• 出版年：1999
• 出版时间：February 10, 1999
• 年：1999
• 卷：121
• 期：5
• 页码：1059 - 1064
• 全文大小：198K
• 年卷期：v.121,no.5(February 10, 1999)
• ISSN：1520-5126

文摘

Electron-transfer rates and electronic coupling factors for ferrocene groups attached to gold electrodesvia oligo(phenylethynyl) "molecular wire" bridges of variable length and structure are reported. Attachmentto gold was achieved via thiol groups at the end of the bridge opposite the ferrocene. Bridge structures weredesigned to promote strong coupling between gold and ferrocene, thereby promoting rapid electron transportover long distances. The effects of bridge length and of substituents on the phenyl rings in the bridge wereaddressed. Bridges containing between three and six phenylethynyl units were studied, and a "beta" value of0.36 Å^-1 describing the exponential distance dependence of bridge-mediated electron-transfer rates was obtained.The effect on the rates of adding two propoxy groups onto one of the phenyl rings in the bridge was examinedand found to be minimal. The standard electron-transfer rate constant of 350 s^-1 obtained for the adsorbatewith the longest bridge (six phenylethynyl units, corresponding to an electron-transfer distance of approximately43 Å) corresponds to an electronic coupling factor between ferrocene and gold of approximately 0.7 cm^-1.The extrapolated rate constants at very short distances were nearly the same for the conjugated bridge seriesand for a related monolayer series in which ferrocene groups were linked to gold via aliphatic bridges. Theextrapolated rate constants at short distance also agree with a calculated rate constant for the limiting case ofadiabatic electron transfer at an electrode.