Electron transfer at electrodes through conjugated 'molecular wire' bridges

Stephen Creager*, C. J. Yu, Cindy Bamdad, Steve O'Connor, Tanya MacLean, Eric Lam, Yoochul Chong, Gary T. Olsen, Jiye Luo, Michael Gozin, Jon Faiz Kayyem

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

419 Scopus citations

Abstract

Electron-transfer rates and electronic coupling factors for ferrocene groups attached to gold electrodes via oligo(phenylethynyl) 'molecular wire' bridges of variable length and structure are reported. Attachment to gold was achieved via thiol groups at the end of the bridge opposite the ferrocene. Bridge structures were designed to promote strong coupling between gold and ferrocene, thereby promoting rapid electron transport over long distances. The effects of bridge length and of substituents on the phenyl rings in the bridge were addressed. Bridges containing between three and six phenylethynyl units were studied, and a 'beta' value of 0.36 Å-1 describing the exponential distance dependence of bridge-mediated electron-transferrates was obtained. The effect on the rates of adding two propoxy groups onto one of the phenyl rings in the bridge was examined and found to be minimal. The standard electron-transfer rate constant of 350 s-1 obtained for the adsorbate with the longest bridge (six phenylethynyl units, corresponding to an electron-transfer distance of approximately 43 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 series and for a related monolayer series in which ferrocene groups were linked to gold via aliphatic bridges. The extrapolated rate constants at short distance also agree with a calculated rate constant for the limiting case of adiabatic electron transfer at an electrode.

Original languageEnglish
Pages (from-to)1059-1064
Number of pages6
JournalJournal of the American Chemical Society
Volume121
Issue number5
DOIs
StatePublished - 10 Feb 1999
Externally publishedYes

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