The redox properties of electroactive self-assembled monolayers (SAMs) on gold in the organic phase were investigated by using the thin-film voltammetry approach, i.e., imposing a thin layer of nitrobenzene between the electrode and the bulk aqueous electrolyte. It was discovered that the structures of binary Fc(CH2)11S-/CH3(CH2)10S-Au SAMs became more homogeneous than in aqueous medium, as indicated by the appearance of a single pair of redox peaks even at high ferrocenylalkanethiolate surface densities. Intermolecular interactions became much weaker and eventually negligible (at low Fc surface density) as confirmed by simulating the experimental cyclic voltammograms (CVs) based on theoretical i-E relationship upon considering a Frumkin isotherm. The formation constant of iFc+⋅ClO4−on pairs in the organic phase was found to be much larger than that in aqueous medium, which reaffirms the predominant influence of the microenvironment around the redox centers (organic medium vs. aqueous electrolyte).

The correlation between redox properties and structural nature in a complete set of mono-ferrocenylpyrimidine derivatives (2-ferrocenylpyrimidine, 2-FcPy; 4-ferrocenylpyrimidine, 4-FcPy; 5-ferrocenylpyrimidine, 5-FcPy) was evaluated by investigating the intramolecular electronic communications. Both conventional electrochemical measurements in organic solvents and thin-film voltammetric studies of these compounds were carried out. It was discovered that their formal potentials are significantly different from each other, and shift negatively in the order of 4-FcPy > 5-FcPy > 2-FcPy. This result suggests that the intramolecular electronic communication is dictated by the delocalization effect of the p-bonding systems in 2-FcPy, and that the electron-withdrawing effect of the nitrogen atoms in the pyrimidine ring plays the key role in 4-FcPy and 5-FcPy. The single crystal X-ray structure analyis and Density Functional Theory (DFT) calculation provided additional evidence (e.g., different torsion angles between the cyclopentadienyl and pyrimidine rings) to support the observed correlation between the redox properties and structural nature. (C) 2014 Elsevier Ltd. All rights reserved.

Ferrocenylalkanethiols are excellent probes to study the structure and properties of mixed self-assembled monolayers (SAMs) on gold; in this paper, the molecular heterogeneity in binary redox-active SAMs on gold prepared via postassembly exchange and coadsorption processes is revealed electrochemically. The exchange process of single-component 11-ferrocenyl-1-undecanethiolate SAMs on gold (FcC11S-Au) with 1-undecanethiol (C11SH) is first investigated; it is shown that a single pair of redox peaks can be obtained upon prolonged immersion in C11SH/ethanol solution. For the coadsorption of FcC11SH and C11SH on gold, the splitting of the redox peak diminishes when the molar ratio FcC11SH decreases to <10%. The binary FcC11S-/C11SAu SAMs with low surface density of ferrocene moieties prepared by these two methods are compared by fitting the cyclic voltammograms (CVs) in considering their intermolecular interactions. The essentially different distributions of the redox centers in these diluted binary SAMs, as indicated by the varied formal potentials and intermolecular repulsion forces, provide further insights in understanding molecular self-assembly processes on the surface.

The intramolecular electronic communication and multilevel ion-pairing effect of triferrocenylmethane（TriFcM） in organic phase was studied with the "thin-layer electrochemistry" approach.Three pairs of symmetric peaks in cyclic voltammetry of TriFcM correspond to three one-electron electrochemical reaction processes and indicate strong intramolecular electronic communication,which could be used to study the multilevel ion-pairing effect.Three different formation constants of ion-pairs between the three ferroceniums of TriFcM and perchlorate in thin organic film were obtained and compared.

The redox behavior of two novel multicenter redox molecules (triferrocenylmethane and triferrocenylmethanol) has been studied in a thin film of nitrobenzene (NB) imposed between a graphite electrode and an aqueous electrolyte. The well separated three sets of redox peaks indicate strong intramolecular electronic communications between the three ferrocene centers in each molecule. They were adapted as model compounds for the study of electron transfer kinetics across the liquid/liquid interface with varied overall driving force using only one-type redox couples in the organic and aqueous phase, respectively. It has been shown that in both cases the dependence of interfacial electron transfer rate on the increased overall driving force across the nitrobenzene/water interface is not monotonic.

We report a new method for detection and oxidation of adsorbed carbon monoxide (CO(ads)) generated from serine on a polycrystalline platinum ultramicroelectrode (UME) by bromine (Br2) using in situ surface interrogation (SI) mode of scanning electrochemical microscopy (SECM). In the SI mode, tip and substrate are both Pt UMEs, and CO(ads) on Pt substrate, generated from serine, can be oxidized by the tip-generated Br2 giving a positive response. Dosing CO(ads) from serine instead of purging CO gas expands the newly introduced reaction of Br2 with CO(ads) and further enhances the hope to get rid of CO(ads) on Pt for fuel cells.

The redox behavior and ion-pairing thermodynamics of ferrocene and its derivatives (dimethylferrocene and decamethylferrocene) in a nitrobenzene (NB) thin film imposed between a graphite electrode and an aqueous electrolyte solution have been studied. We have shown that the presence of supporting electrolytes in the organic phase complicates their redox behavior, i.e., both,the oxidation potential and peak area change significantly with time. In the absence Of Supporting electrolytes in the NB phase, the redox potential of the ferrocene molecules also shifts when the concentration of the supporting electrolytes (NaClO4 or HClO4) in the aqueous phase varies. It has been confirmed upon considering the influence of liquid-liquid junction potential that such a potential shift is dictated by the formation of ion pairs between the electrochemically generated ferricenium cations and the counteranions in the organic phase. On the basis of the determination of anion (ClO4-) concentrations in the NB film, we were able to quantitatively evaluate the correlation between molecular structure and the formation constant of Fc(+)center dot ClO4- ion pairs.