Publication 685

J. Am. Chem. Soc., 133 (19), 7509-7516, 2011 DOI: 10.1021/ja201042h
Do molecular conductances correlate with electrochemical rate constants? experimental insights

Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua, Zhejiang 321004, China - Chemistry Department and State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China - UMR CNRS 8640 Pasteur, Ecole Normale Supérieure, Université Pierre et Marie Curie Paris 06, 24 rue Lhomond, 75231 Paris Cedex 05, France - Laboratoire de Chimie Analytique et d’Electrochimie, Département de Chimie, Faculté des Sciences de Tunis, Université El-Manar, 2092 Tunis El-Manar, Tunisia - LISE-Laboratoire Interfaces et Systêmes Electrochimiques, UPR 15 du CNRS, Université Pierre et Marie Curie Paris 06, Case Courrier no. 133, 4 place Jussieu, 75252 Paris Cedex 05, France - Laboratoire d’Electrochimie Moléculaire, UMR CNRS 7591, Université Paris Diderot, 15 rue Jean-Antoine de Baïf, 75205 Paris Cedex 13, France

We measured single-molecule conductances for three different redox systems self-assembled onto gold by the STMBJ method and compared them with electrochemical heterogeneous rate constants determined by ultrafast voltammetry. It was observed that fast systems indeed give higher conductance. Monotonous dependency of conductance on potential reveals that large molecular fluctuations prevent the molecular redox levels to lie in between the Fermi levels of the electrodes in the nanogap configuration. Electronic coupling factors for both experimental approaches were therefore evaluated based on the superexchange mechanism theory. The results suggest that coupling is surprisingly on the same order of magnitude or even larger in conductance measurements whereas electron transfer occurs on larger distances than in transient electrochemistry.