Christian Amatore, Emmanuel Maisonhaute
in collaboration with H. D. Abruña ( Cornell University ) and J-F. Nierengarten (Université Louis Pasteur, Strasbourg )

In macromolecules bearing several redox centers, direct electron transfer between some redox centers and the electrode is sometimes extremely slow because of their large distance to the surface. This configuration favors a multistep electron transfer by electron hopping from site to site. Through this mecanism, all redox centers of the molecule may be attained by the electrochemical perturbation. The registered signal will then depend on the shape of the macromolecule, on the intra-molecular rate of electron transfer and also on the time for which the electrochemical perturbation is allowed to propagate.

This situation has been analysed quantitatively in the case of a PAMAM dendrimer functionalized by 64 Ru(terpy)₂ redox centers. Indeed, even if these compounds do not specifically possess an anchorage group, the sum of numerous Van der Waals interactions with the surface is so important that these compounds spontaneously adsorb on the electrode surface to form monolayers. For our PAMAM dendrimer, intramolecular electron hopping is very fast, so that voltammetric scan rates in the megavolt per second range are necessary to follow the electron transfer kinetics. This evidences an important mobility of the redox centers on the dendrimer surface.

Another dendrimer functionalised by 24 C₆₀ fullerenes can form bilayers onto the electrode. In this case, our work allowed to identify the redox communication between the first and the second layer, because the corresponding intermolecular electron exchange is slower than the intramolecular one.

References

Precise Adjustement of Nanometric-Scale Diffusion Layers Within a Redox Dendrimer Molecule by Ultrafast Cyclic Voltammetry : an Electrochemical Nanometric Microtome.
C. Amatore, Y. Bouret, E. Maisonhaute, H. D. Abruña, J. I. Goldsmith. Chemphyschem, 2, 2001, 130-134.

Ultrafast Voltammetry of Adsorbed Redox Active Dendrimers with Nanometric Resolution : An Electrochemical Microtome.
C. Amatore, Y. Bouret, E. Maisonhaute, H. D. Abruña, J. I. Goldsmith. Chem. Eur. J., 7, 2001, 2206-2226.

When Voltammetry Reaches Nanoseconds.
C. Amatore, E. Maisonhaute, Anal. Chem., 77, 2005, 303A-311A.

Synthesis and electrochemical properties of fullerene-rich nanoclusters resulting from the cobalt-catalysed cyclotrimerization of bis-arylalkyne fullerodendrimers.
U. Hahn, C. Amatore, E. Maisonhaute, J.-F. Nierengarten, Angew. Chem. Int. Ed., 46, 2007, 951-954. (Abstract + PDF)

Fullerodendrimers with a tris-isothiocyanate core allowing their anchoring onto gold electrodes.
J. A. Camerano, M. A. Casado, U. Hahn, J-F. Nierengarten, E. Maisonhaute, C. Amatore, New J. Chem., 31, 2007, 1395-1399. (Abstract + PDF)