Molecular Sieving and Current Rectification Properties of Thin Organic Films

Abstract

For the purpose of preparing well-organized functional surfaces, carbon and gold substrates were modified using electroreduction of a tetrahedral-shape preorganized tetra-aryldiazonium salt, leading to the deposition of ultrathin organic films. Characterization of the modified surfaces has been performed using cyclic voltammetry, X-ray photoelectron spectroscopy, infrared absorption spectroscopy, ellipsometry, atomic force microscopy, and contact angle measurements. The specific design of the tetra-aryldiazonium salts leads to an intrinsic structuring of the resulting organic films, allowing molecular sieving and current rectification properties toward redox probes in solution.

Effect of Electrolyte Ions on the Formation, Electroactivity, and Rectification Properties of Films Obtained by Electrografting

“…The chemically irreversible behavior of the oxidation process of ferrocene has been previously observed for other modified electrodes and is known as a current rectification phenomenon . This phenomenon was recently re‐examined for electrodes modified by reduction of tetra‐aryldiazonium salts in the framework of both the redox probe size and bulky nature of the supporting electrolyte ions, whose transport inside the channels of the grafted films was proposed to be essential for the rectification behavior …”

“…[39][40][41] This phenomenon was recently re-examined for electrodes modified by reduction of tetra-aryldiazonium salts in the framework of both the redox probe size and bulky nature of the supporting electrolyte ions, whose transport inside the channels of the grafted films was proposed to be essential for the rectification behavior. [42] Therefore, considering the previous antecedents and the results shown in Figures 6C and 6D, an alternative approach to explain the rectification phenomenon was proposed. In these last two systems, the bulky and hydrophobic nature of both n-Bu 4 N + and n-Hx 4 N + cations allows a lower ionic occupation inside the film channels, which facilitates consequently the entrance of ferrocene inside these channels, a kind of surface inclusion complex that keep some analogy with the inclusion of redox active molecules inside the cavities of different compounds like the cyclodextrins.…”

Electrografting of Carbon Surfaces with Aliphatic Chains and its Effect on the Rectification of Ferrocene as Redox Probe in Solution

“…Contrasting with these features, the voltammogram of ferrocene on the electrode modified by mediated oxidation of octanoate shows a well‐defined oxidation peak, but without its corresponding reduction peak. This behavior corresponds to a rectification phenomenon, which can also be explained by changes in the mass transport properties inside the film channels (see next section) [30,31] . In this case, mass transport of ferrocene is favored by a higher size of these channels, which are formed during electrografting because of the major number of conformational freedom degrees of the heptyl chains in the polymeric film structure.…”

“…In agreement with this last property, the size of the redox probe as well as the size of the supporting electrolyte ions are regarded as determining factors of a rectification phenomenon observed during cyclic voltammograms of the redox probe [30] . This rectification was first associated with the behavior of redox probes on grafted electrodes bearing electrochemically active groups, however, it occurs also for films without redox groups, which means that the phenomenon could also be related to the hydrophilic or hydrophobic properties of the grafted film as well as the capability of the redox probes and the supporting electrolyte ions to permeate the channels in the grafted film [30,31] . Therefore, in this work, the surface of glassy carbon electrodes was modified with non‐electrochemically active films that bear saturated aliphatic chains of different length.…”

“…The permeation of the redox probe and the supporting electrolyte ions inside the film channels is also considered as an evidence of its sieving properties [28,29] . In agreement with this last property, the size of the redox probe as well as the size of the supporting electrolyte ions are regarded as determining factors of a rectification phenomenon observed during cyclic voltammograms of the redox probe [30] . This rectification was first associated with the behavior of redox probes on grafted electrodes bearing electrochemically active groups, however, it occurs also for films without redox groups, which means that the phenomenon could also be related to the hydrophilic or hydrophobic properties of the grafted film as well as the capability of the redox probes and the supporting electrolyte ions to permeate the channels in the grafted film [30,31] .…”