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Four different ionic liquids, based on 1-alkyl-3-methylimidazolium or quaternary ammonium cations, were used as reaction media for several typical electrochemical reactions with a strict control of the residual water concentration. The oxidation of organic molecules (anthracene, naphthalene, durene, 1,4-dithiafulvene, and veratrole) for which the cation radicals undergo first and second-order kinetics reactions were investigated in ionic liquids and compared with their behavior in acetonitrile. From the analysis of the voltammetric current responses, the reaction mechanism was established and the thermodynamic and kinetics parameters were extracted. The most interesting result is that the nature of investigated mechanisms is almost unchanged in ionic liquids as compared with conventional organic media. A decrease of the electron-transfer kinetics from the aromatic molecules to the electrode (around 1 order of magnitude) is observed for all of the studied molecules, indicating an higher solvent reorganization during the charge transfer. The kinetics of the chemical reactions triggered by the electron transfer are slightly affected by the use of ionic liquid. The only noticeable effect is a decrease of the bimolecular reactions rates partly due to a lowering of the limiting diffusion-controlled kinetics rate constant together with a specific solvation effect of reactants in these special media. These preliminary electrochemical experiments appear as encouraging results for the use of ionic liquids in a “green” electrochemistry.

An essential issue in the development of materials presenting an accurately functionalized surface is to achieve control of layer structuring. Whereas the very popular method based on the spontaneous adsorption of alkanethiols on metal faces stability problems, the reductive electrografting of aryldiazonium salts yielding stable interface, struggles with the control of the formation and organization of monolayers. Here we report a general strategy for patterning surfaces using aryldiazonium surface chemistry. Calix[4]tetra-diazonium cations generated in situ from the corresponding tetra-anilines were electrografted on gold and carbon substrates. The well-preorganized macrocyclic structure of the calix[4]arene molecules allows the formation of densely packed monolayers. Through adequate decoration of the small rim of the calixarenes, functional molecules can then be introduced on the immobilized calixarene subunits, paving the way for an accurate spatial control of the chemical composition of a surface at molecular level.

Multielectronic O(2) reduction reactions (ORR) at Pt surface (and at Au surface for comparison purpose) were examined both in water and in organic solvents using a strategy based on radical footprinting and scanning electrochemical microscopy (SECM). Experiments reveal a considerable and undocumented production of OH radicals when O(2) is reduced at a Pt electrode. These observations imply that the generally admitted description of ORR as simple competitive pathways between 2-electron (O(2) to H(2)O(2)) and 4-electron (O(2) to H(2)O) reductions is often inadequate and demonstrate the occurrence of another 3-electron pathway (O(2) to OH radical). This behavior is especially observable at neutral and basic pH's in water and in organic solvents like dimethylformamide or dichloromethane. In view of the high reactivity of OH radical versus organic or living materials, this observation could have important consequences in several practical situations (fuel cells, sensors, etc.) as far as O(2) reduction is concerned. This also appears as a simple way to locally produce highly reactive species as exemplified in the present work by the micropatterning of organic surfaces.

No abstract

Electroactive polyfluorene films were obtained by anodic coupling of fluorene and a series of 9,9-disubstituted fluorenes and their related 2,7‘-dimers and trimer. The polymerization mechanism is discussed in light of cyclic voltammetry investigations in organic media using the classical millimetric electrode and ultramicroelectrodes, DFT theoretical calculations, and laser flash photolysis experiments. The first step of electropolymerization involves the formation of the carbon−carbon bond through the coupling between two fluorene radical cations. However, the radical cation of the produced dimer is not reactive enough to repeat the coupling reaction as in the classical electropolymerization mechanism. To continue the polymerization, formation of a higher oxidation state is required. This behavior is supported by theoretical expectations.

Gold nanoparticles stabilized with a thin layer of post-functionalizable calix[4]arenes were prepared through the reductive grafting of a calix[4]arene-tetra-diazonium salt. These particles show exceptional stability towards extreme pH, F(-), NaCl, and upon drying. Post-functionalization of the calix-layer was demonstrated, opening the way to a wide range of applications.

Electron transfer (ET) kinetic rate constants k s in Ethaline (1:2 Choline Chloride + Ethylene Glycol) have been measured for two common redox couples (ferrocene/ferrocenium and ferrocyanide/ferricyanide) on a glassy carbon electrode and compared with ET kinetics in ionic liquids and classical organic solvents in the same conditions (acetonitrile and water). A particular care has been taken to treat ohmic drop in DES. For both couples, we found that ET rate constants are just a little lower than those measured in classical solvents (around 50% or less). These results contrast with ET rates in ionic liquids where electron transfers are considerably slower (100 times lower). Data are discussed as function of the solvent relaxation time using Marcus Theory for an adiabatic electron transfer.