Alain Deronzier

Photocatalysis of the Pschorr reaction by tris-(2,2′-bipyridyl)ruthenium(II) in the phenanthrene series

The photocatalytic conversion of the tetrafluoroborate salt of the stilbenediazonium ion (1) into the corresponding phenanthrene (2)(Pschorr reaction) by Ru(bpy)32+(bpy = 2,2′-bipyridyl) has been investigated. We have shown that this particular Pschorr reaction takes place quantitatively with a high quantum yield (φ > 0.4) upon selective photoexcitation of a catalytic amount of Ru(bpy)32+. Quenching and conventional flash photolysis experiments have revealed that quenching of the excited state of Ru(bpy)32+ probably occurs by an electron-transfer process. In contrast it has been shown that direct photolysis of (1) leads to the Pschorr reaction with a poorer yield (10–20%).

Electrochemical coating of a platinum electrode by a poly(pyrrole) film containing the fac-Re (2,2'-bipyridine) (CO)3Cl system. Application to electrocatalytic reduction of CO2

Donnees sur la preparation et le comportement electrochimique des electrodes de Pt recouvertes de films de polypyrrole contenant des complexes de Re(I) avec le bipyridyle

Oxidative electropolymerization of polypyridinyl complexes of ruthenium(II)-containing pyrrole groups

Abstract The oxidative electrochemical polymerization of polypyridinyl complexes of ruthenium(II) that contain pyrrolic groups on their surrounding ligands have been investigated. Film formation and stability of the resulting modified electrodes have been studied with regard to the number of pyrrolic groups and 2,2′-bipyridinyl ligands contained in the complexes. Observation of prepeaks in the cyclic voltammograms of the modified electrodes is attributed to the mediated oxidation and reduction of the polypyrrole backbone through the redox levels of the Ru(II) complexes. The polypyrrolic chain does not exhibits its usual electroactivity, probably owing to the steric hindrance due to the bulky polypyridinyl Ru(II) pendant groups.

Photo-oxidation of some carbinols by the Ru(II) polypyridyl complex-aryl diazonium salt system

Abstract The Ru(II) polypyridyl complex 2 effectively catalyzed the photo-oxidation by visible light of some carbinols to aldehydes in presence of a diazonium salt as quencher and a basic agent in acetonitrile.

Efficient and limiting reactions in aqueous light-induced hydrogen evolution systems using molecular catalysts and quantum dots.

Hydrogen produced from water and solar energy holds much promise for decreasing the fossil fuel dependence. It has recently been proven that the use of quantum dots as light harvesters in combination with catalysts is a valuable strategy to obtain photogenerated hydrogen. However, the light to hydrogen conversion efficiency of these systems is reported to be lower than 40%. The low conversion efficiency is mainly due to losses occurring at the different interfacial charge-transfer reactions taking place in the multicomponent system during illumination. In this work we have analyzed all the involved reactions in the hydrogen evolution catalysis of a model system composed of CdTe quantum dots, a molecular cobalt catalyst and vitamin C as sacrificial electron donor. The results demonstrate that the electron transfer from the quantum dots to the catalyst occurs fast enough and efficiently (nanosecond time scale), while the back electron transfer and catalysis are much slower (millisecond and microsecond time scales). Further improvements of the photodriven proton reduction should focus on the catalytic rate enhancement, which should be at least in the hundreds of nanoseconds time scale.

Electrocatalytic reduction of CO2 into formate with [(η5Me5C5)M(L)Cl]+ complexes (L = 2,2′-bipyridine ligands; M Rh(III) and Ir(III))

Abstract The ability of [( η 5 Me 5 C 5 )M(L)Cl] + (L = 2,2−bipyridine ligands; M = Rh(III) and Ir(III) to act as an electrocatalyst for CO 2 reduction has been examined in an aqueous organic medium. It appears that the Rh(III) complex is a better catalyst than the Ir(III) one, and that a current efficiency for formate production of up to 50% can be reached. The initial step of the electrocatalysis involves the formation of the corresponding hydrido complex. Immobilization of such catalysts on the electrode surface, by the technique of functionalized polypyrrole films, decreases their efficiency as a consequence of the lower efficiency of the insertion of CO 2 into the metal-hydride bond.

Electrocatalytic reduction of CO2 in water on a polymeric [{Ru0(bpy)(CO)2}n](bpy = 2,2′-bipyridine) complex immobilized on carbon electrodes

The electrocatalytic reduction of CO2 on a carbon/[{Ru0(bpy)(CO)2}n](bpy = 2,2′-bipyridine) modified electrode, prepared by electrochemical reduction of [RuII(bpy)(CO)2Cl2], leads to the selective and quantitative formation of CO even in pure aqueous electrolyte; the stability of the modified cathode is improved by using a preformed polypyrrolic film functionalized with this complex.

Electrochemical oxidation of carbinols mediated by nitroxyl radicals in solution or bonded to polypyrrolic coatings on platinum and carbon electrodes

Abstract Electrochemical oxidations of carbinols mediated by the 2,2,5,5-tetramethyl—3-pyrrolin—1-oxyl, via its nitrosonium ion, have been investigated. Studies have been carried out with the mediator either in solution or deposited in a film form at the surface of an electrode by electropolymerization of a monomer containing pyrrole groups covalently bonded to the nitroxyl moiety.

Long-Lived Charge Separated State in NiO-Based p-Type Dye-Sensitized Solar Cells with Simple Cyclometalated Iridium Complexes

Three new cyclometalated iridium complexes were prepared and investigated on nanocrystalline NiO cathodes. Nanosecond transient absorption spectroscopy experiments show they present a surprisingly slow geminate charge recombination upon excitation on NiO, representing thus the first examples of simple sensitizers with such feature. These complexes were used in dye-sensitized solar cells using nanocrystalline NiO film as semiconductor. The long-lived charge separated state of these Ir complexes make them compatible with other redox mediators than I3(-)/I(-), such as a cobalt electrolyte and enable to reach significantly high open circuit voltage.

Photo-oxidation of tris(2,2′-bipyridine)ruthenium(II) by para-substituted benzene diazonium salts in acetonitrile. Two-compartment photoelectrochemical cell applications

The photo-oxidation of tris(2,2′-bipyridine)ruthenium(II)[Ru(bpy)2+3] by substituted benzene diazonium salts (p-RC6H4N+2) has been studied in acetonitrile. Quenching of the excited state [Ru(bpy)2+*3] by p-RC6H4N+2 takes place at diffusional rates (kq 1.6 × 1010 dm3 mol–1 s–1) and leads to the effective build-up of the oxidized species Ru(bpy)3+3 with a high quantum yield (ϕ > 0.12). ϕ depends on the nature of the substituent R. This Ru(bpy)2+*3/p-RC6H4N+2 system has been applied in some two-compartment photoelectrochemical cells. The photogenerated Ru(bpy)3+3 oxidizes an electron donor D in the dark compartment. Features of this cell are reported, especially the influence of D on the open-circuit photovoltage and the photocurrent passing through a 1000 Ω resistor. The performance of this cell has been improved by the use of a second irradiation compartment where D is photogenerated as the reduced form of the 1,1′-dimethyl-4,4′-bipyridinium dication.