Fabien Miomandre

Synthesis of new substituted tetrazines: electrochemical and spectroscopic properties

Original tetrazines substituted by heterocyclic rings have been prepared. Their syntheses, as well as their electrochemical and spectroscopic features, are described. Calculations have also been made on the cation radicals, anion radicals and neutral compounds and are in correct agreement with the experimental results. All compounds are electroactive, both in oxidation and reduction, and display two absorption bands in the UV and visible regions of the spectrum. Reduction potentials and maximum wavelengths are correlated with the electron-rich character of the heterocyclic substituent on the tetrazine ring. None of these compounds gives good quality polymers upon electro-oxidation, which was unexpected, especially for the bis(2-pyrrolyl) tetrazine. This latter result can be explained by the occurrence of a self-deprotonation equilibrium in the cation radical.

Fluorescence microscopy coupled to electrochemistry : a powerful tool for the controlled electrochemical switch of fluorescent molecules

The first-time coupling of fluorescence microscopy with a three-electrode electrochemical cell is described and applied to the investigation of a controlled-potential redox switch of organic fluorophores such as tetrazine derivatives.

Polypyridyl ruthenium complexes as coating agent for the formation of gold and silver nanocomposites in different media. Preliminary luminescence and electrochemical studies

Three polypyridyl ruthenium complexes, [(phen)2Ru(2,2′-p-phenylene-bis(imidazo[4,5-f][1,10])phenanthroline)](X)2 (1·X2), [(phen)2Ru((4-pyridine)oxazo[4,5-f][1,10]phenanthroline)](X)2 (2·X2) and [(phen)2Ru((3-thiophene)imidazo[4,5-f][1,10]phenanthroline)](X)2 (3·X2), X− = PF6− or Cl−, have been used to functionalize and stabilize gold and silver nanoparticles in aqueous and non aqueous (acetonitrile) media. Direct interaction between the metallic nanoparticles and the ruthenium complexes was ensured by bidentate chelating phenanthroline (1), monodentate pyridine (2) or monodentate thiophene (3) groups. The influence of several parameters was studied in order to control the size, shape and stability of the nanocomposites thus formed: the nature of the metallic nanoparticles, the nature of the coating ruthenium complex, the ratio R = [Mn+]/[Ru2+] (M = Ag or Au) and the solvent. The colloidal solutions have been characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Preliminary electrochemical and luminescence measurements have shown the influence of the metallic nanoparticle on the properties of the ruthenium complexes.

Electrochemical, linear optical, and nonlinear optical properties and interpretation by density functional theory calculations of (4-N,N-dimethylaminostyryl)-pyridinium pendant group associated with polypyridinic ligands and respective multifunctional metal complexes (Ru(II) or Zn(II)).

The synthesis, linear optical and nonlinear optical properties, as well as the electrochemical behavior of a series of pro-ligands containing the 4-(4-N,N-dimethylaminostyryl)-1-methyl pyridinium (DASP(+)) group as a push-pull moiety covalently linked to terpyridine or bipyridine as chelating ligands are reported in this full paper. The corresponding multifunctional Ru(II) and Zn(II) complexes were prepared and investigated. The structural, electronic, and optical properties of the pro-ligands and the ruthenium complexes were investigated using density functional theory (DFT) and time-dependent (TD) DFT calculations. A fairly good agreement was observed between the experimental and the calculated electronic spectra of the pro-ligands and their corresponding ruthenium complexes. A quenching of luminescence was evidenced in all ruthenium complexes compared with the free pro-ligands but even the terpyridine-functionalized metal complexes exhibited detectable luminescence at room temperature. Second order nonlinear optical (NLO) measurements were performed by Harmonic Light Scattering and the contribution of the DASP(+) moieties (and their relative ordering) and the metal-polypyridyl core need to be considered to explain the nonlinear optical properties of the metal complexes.

New conjugated polymerizable pyrrole and 2,5-dithienylpyrrole azobenzene dyes: synthesis and spectroelectrochemical properties

We describe the first easy syntheses of new fully conjugated monomers and their derived polymers containing a photoisomerizable azobenzene group, along with their electrochemical properties. Two classes of compounds have been studied differing in the nature of the polymerizable unit: pyrrole or 2, 5-dithienylpyrrole. A rather effective electronic interaction between the pyrrole and azo moieties has been demonstrated, while the conjugation is much less pronounced in the case of the terheterocycle. This behavior has been ascribed to a twisted conformation of the 2,5-dithienylpyrrole compounds in the neutral form, as demonstrated by theoretical modeling. All these molecules are electropolymerizable monomers, although the 2,5-dithienylpyrrole compounds lead only to thin films of conducting polymers when compared to their pyrrole analogs.

Electrochemical behaviour of iron(III) salen and poly(iron–salen). Application to the electrocatalytic reduction of hydrogen peroxide and oxygen

Abstract The electropolymerisation of the iron(III) salen complex is reported, as well as the electrochemical behaviour of the monomer. High scan rate cyclic voltammetry allows us to calculate the lifetime of the cation radical generated during oxidation. Although the films are more difficult to prepare than several other poly(metal–salen) films (e.g. with nickel or copper), poly(iron–salen) can be well characterised by electrochemistry, either in organic or aqueous medium. The efficiency of the films towards the catalytic electroreduction of hydrogen peroxide and oxygen has been tested, and a different kinetic behaviour has been observed for both substrates, with a much greater efficiency in the case of oxygen.

Redox- and Protonation-Induced Fluorescence Switch in a New Triphenylamine with Six Stable Active or Non-Active Forms

The synthesis, photophysical and electrochemical properties as well as theoretical calculation studies of a newly designed triphenylamine derivative are described. This original compound displays one neutral form, three oxidized forms, and two protonated forms with distinct photophysical characteristics. The interplay of the emission with the protonation or the redox state (electrofluorochromism) has been explored and an on-off-on-off fluorescence switching was observed in the case of oxidation and an on-on-off fluorescence switching in the case of protonation.

Redox-controlled fluorescence modulation (electrofluorochromism) in triphenylamine derivatives

The study of the chemical and electrochemical fluorescence switching properties of a family of substituted triphenylamine derivatives is reported. First of all, the synthesis of a family of six compounds is described. They are characterized by electrochemistry, UV-vis and fluorescence spectroscopy and spectroelectrochemistry. Theoretical calculations were performed in order to corroborate the experimental results. While these compounds emit blue to green light under UV irradiation with a large quantum yield (37%) in the case of one molecule, the fluorescence intensity is quenched upon oxidation. The fluorescence behavior can be switched between the strong fluorescent (neutral) state and the non-fluorescent (oxidized) state with a high contrast (around 1500 for the fluorescence intensity for one of these molecules). Furthermore, the chromatic contrast of three of these molecules reaches 70% that can be important for further applications.

Synthesis and the electrochemical and fluorescence properties of new cyclophane-derivatized oligothiophenes

Several new oligothiophenes blocked by cyclophane end groups with 2, 3, 4 or 6 thiophene rings in the chain have been prepared and studied by electrochemistry and by UV-visible and fluorescence spectroscopy. Both radical cations and dications are stable, even for the bithiophene compound; besides the stabilization induced by the blocking of the reactive α positions, this strongly suggests electronic connection between the cyclophanes and the oligothiophene chains, especially for the shorter compounds. All the molecules are strongly fluorescent with increasing quantum yields up to 4 thiophene rings. The assumption of a conjugation between the cyclophane end groups and the oligothiophene main chain is also supported by the UV-visible and fluorescence results, since the spectroscopic data correlate well with (n + 2)−1 instead of n−1, with n representing the number of thiophene rings in the oligomer.

Unprecedented Self-Organized Monolayer of a Ru(II) Complex by Diazonium Electroreduction.

A new heteroleptic polypyridyle Ru(II) complex was synthesized and deposited on surface by the diazonium electroreduction process. It yields to the covalent grafting of a monolayer. The functionalized surface was characterized by XPS, electrochemistry, AFM, and STM. A precise organization of the molecules within the monolayer is observed with parallel linear stripes separated by a distance of 3.8 nm corresponding to the lateral size of the molecule. Such organization suggests a strong cooperative process in the deposition process. This strategy is an original way to obtain well-controlled and stable functionalized surfaces for potential applications related to the photophysical properties of the grafted chromophore. As an exciting result, it is the first example of a self-organized monolayer (SOM) obtained using diazonium electroreduction.