title: Experimental study of the interplay between long-range electron transfer and redox probe permeation at self-assembled monolayers: evidence for potential-induced ion gating.
abstract: Evidence for the competition between long-range electron transfer across self-assembled monolayers (SAMs) and incorporation of the redox probe into the film is reported for the electroreduction of Ru(NH(3)) at hydroxyl- and carboxylic-acid-terminated SAMs on a mercury electrode, by using electrochemical techniques that operate at distinct time scales. Two limiting voltammetric behaviors are observed, consistent with a diffusion control of the redox process at mercaptophenol-coated electrodes and a kinetically controlled electron transfer reaction in the presence of neutral HS-(CH(2))(10)-COOH and HS-(CH(2))(n)()-CH(2)OH (n = 3, 5, and 10) SAMs. The monolayer thickness dependence of the standard heterogeneous electron transfer rate constant shows that the electron transfer plane for the reduction of Ru(NH(3)) at hydroxyl-terminated SAMs is located outside the film | solution interface at short times. However, long time scale experiments provide evidence for the occurrence of potential-induced gating of the adsorbed structure in some of the monolayers studied, which takes the form of a chronoamperometric spike. Redox probe permeation is shown to be a kinetically slow process, whose activation strongly depends on redox probe concentration, applied potential, and chemical composition of the intervening medium. The obtained results reveal that self-assembled monolayers made of mercaptobutanol and mercaptophenol preserve their electronic barrier properties up to the reductive desorption potential of a fully grown SAM, whereas those of mercaptohexanol, mercaptoundecanol, and mercaptoundecanoic acid undergo an order/disorder transition below a critical potential, which facilitates the approach of the redox probe toward the electrode surface.
authors.affiliation: Departamento de Quimica Fisica, Facultad de Quimica, Universidad de Sevilla, 41012, Sevilla, Spain.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Calvente
authors.forename: German
authors.initials: G
authors.lastname: López-Pérez
authors.forename: Pablo
authors.initials: P
authors.lastname: Ramírez
authors.forename: Héctor
authors.initials: H
authors.lastname: Fernández
authors.forename: María Alicia
authors.initials: MA
authors.lastname: Zón
authors.forename: Willem H
authors.initials: WH
authors.lastname: Mulder
authors.forename: Rafael
authors.initials: R
authors.lastname: Andreu