Biomedical subjects

Christophe Coudret

Publications and source records attributed to Christophe Coudret.

7 recordsLinked to original sources

PubMed2006

Electron-triggered motions in technomimetic molecules.

Technomimetic molecules are molecules designed to imitate macroscopic objects at the molecular level, also transposing the motions that these objects are able to undergo. This article focuses on technomimetic molecules with motions triggered by electrons. The first part is devoted to our work in the field of molecular switches: after having demonstrated the possibility of controlling an intramolecular electron transfer by photoisomerisation, we are now trying to control the isomerisation, either by electrochemistry, or by embedding the photochromic compound in a self-assembled monolayer and testing the electrical conduction with a STM tip. In a second part, we present our strategy on controlling the rotation in a molecular rotary motor and the family of ruthenium complexes designed to perform such a task. The molecules have a piano-stool structure with a "stator" meant to be grafted on an oxide surface, and a "rotor" bearing redox-active groups, so that addressing the molecule with nano-electrodes would trigger rotation. The electrical control of the charge state of a molecule by a STM tip is developed in a final part.

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PubMed2005

Deformation of a "rigid" molecule in self-assembled nanostructures.

A simple spirobifluorene molecule with pseudotetrahedral structure was investigated for its supposed conformational resilience upon adsorption. Through deposition at room temperature of this molecule on a Cu(111) surface and subsequent observation at 5 K with an ultrahigh vacuum scanning tunneling microscope, this "rigidity" upon physisorption is confirmed. However, an unexpected chemisorbed state was also found with the molecules arranged in trimers. The unique coexistence of physisorbed and chemisorbed states on the same substrate is thus demonstrated at the early stage of self-assembly.

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PubMed2005

Understanding electrochromic processes initiated by dithienylcyclopentene cation-radicals.

Simple photochromic dithienylethylenes with either a perfluoro or a perhydro cyclopentene ring, and a variety of substituents (chlorine, iodine, trimethylsilyl, phenylthio, aldehyde, carboxylic acid, and ethynylanisyl), have been prepared and their electrochemical behavior was explored by cyclic voltammetry. All dithienylethylenes present two-electron irreversible oxidation waves in their open form, but the cation-radical of the open isomers can follow two different reaction pathways: dimerization or ring closure, whereas the halogen derivatives follow a dimerization mechanism, the presence of donor groups, such as the phenylthio-substituted compound, promote an efficient oxidative ring closure following an ECE/DISP mechanism. Electrochromic properties are also found in the corresponding ring-closed isomers. Depending on the substituents on the thiophene ring, and the perfluro or perhydro cyclopentene ring, open isomers can be obtained from oxidation (chemical or electrochemical) of the corresponding ring-closed isomers via an EC mechanism. This reaction pathway is favored by the presence of electron-withdrawing groups in the molecule. For all these compounds, closed or open, the oxidation lies between 0.8 and 1.5 V vs SCE, and provokes a permanent modification of the color, even after an oxidation-reduction cycle. This could be qualified as "electrochromism with memory". On the other hand, the ring-closed electron-rich isomers (E degrees < 0.8 V), which show reversible waves at the cation-radical or even dication level, give rise to "true electrochromism", for which no structural changes are observed. The experimental study was completed by theoretical calculations at the DFT level, using B3LYP density functional, which gave information on the total energy, the geometry, and the electronic structures of several representative compounds, either in the neutral form or in the cation-radical state. These results are important for the potential design of photochromic systems, such as three-state conjugated systems and photoelectrical molecular switching devices.

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PubMed2005

Tailoring the mobility of a 3D molecule adsorbed on a metal surface.

Because of its tetrahedral structure, spirobifluorene is an innovative molecule for molecular mechanics studies by means of scanning tunneling microscopy. On Cu(100), it was observed only anchored at defects because of its mobility at room temperature. To frustrate its diffusion, it was functionalized with phenyl and thiophene groups. Tetraphenylspirobifluorene is also mobile on Cu(100), whereas tetrathienylspirobifluorene is fixed in the middle of the terraces. This very different behavior is an original and unexpected result because both benzene and thiophene are reported to be weakly bound to Cu(100) with almost the same adsorption energy.

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PubMed2003

Molecular wires built from binuclear cyclometalated complexes.

Binuclear complexes with cyclometalated ends of the [Ru(bpy)(2)(ppH)](+) type (bpy = 2,2'-bipyridine, ppH = 2-phenylpyridine), linked by various spacers, have been prepared. These spacers are made of one or two triple bonds, or bis-ethynyl aryl groups, with aryl = benzene, thiophene, or anthracene. The complexes with bis-ethynyl aryl spacers are obtained by Sonogashira couplings with suitable bis-alkynes, starting from the [Ru(bpy)(2)(ppBr)](+) synthon. Complexes with one or two triple bonds are obtained from the true alkyne [Ru(bpy)(2)(pp-CCH)](+) cyclometalated precursor, using respectively a Sonogashira coupling with the iodo derivative [Ru(bpy)(2)(ppI)](+), or an oxidative homocoupling. Some complexes with tert-butyl-substituted bipyridine ancillary ligands have also been obtained. Oxidation of the binuclear complexes occurs near 0.5 V, i.e., more easily than with [Ru(bpy)(3)](2+)-based complexes. A single anodic wave is observed, with almost no detectable splitting, corresponding to two closely spaced one-electron processes. Differential pulse voltammetry allows the determination of the corresponding comproportionation constants involving the mixed valence Ru(II)[bond]Ru(III) forms. Controlled potential electrolysis yields the mixed valence forms in comproportionation equilibrium with homovalent forms. Analysis of the intervalence transitions allows the calculation of the electronic coupling element V(ab). This series of complexes exhibit relatively large couplings when comparing with complexes of similar metal-metal distances, with a special mention for the anthracene-containing spacer, which appears particularly efficient for mediating the metal-metal interaction. The results can be rationalized by theoretical calculations at the extended Hückel level.

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PubMed2003

An approach to long and unsubstituted molecular wires: synthesis of redox-active, cationic phenylethynyl oligomers designed for self-assembled monolayers.

Various oligo(phenyleneethynylene)s (OPEs) have been synthesized in the past, as they are considered as prototypes of molecular wires. When the oligomers are capped by a redox site at one end and a thiol at the other end, the resulting molecules can be grafted as a self-assembled monolayer on a gold electrode and fully studied by electrochemical techniques. Unfortunately, such molecules are usually poorly soluble and require the incorporation of solubilizing pendant groups. In this paper, we show that the replacement of the classically used redox group ferrocene by a cationic organometallic ruthenium complex, namely, [Ru(bipy)(2)(ppH)](+) (bipy, 2,2'-bipyridine; ppH, 2-(2'-yl-phenyl)pyridine), allows a concise synthesis of an unsubstituted thioacetate-capped OPE up to four repetitive units long. The positive charge does not interfere with the conventional organic chemistry used to elongate, purify, or characterize the hexafluorophosphate salts of the molecules. To our knowledge, this represents the first family of long, poorly substituted OPEs designed for self-assembly.

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PubMed2002

A new redox site as an alternative to ferrocene to study electron transfer in self-assembled monolayers.

The cyclometallated ruthenium complex [Ru(bpy)2(pp)]+ (bpy: 2,2'-bipyridine; pp: 2-(2'-ylphenyl)pyridine) was easily grafted to a omega-alkanethiol and the resulting compound was coadsorbed with 11-hydroxyundecanethiol on gold yielding a Self-Assembled Monolayer (SAM) in an analogous manner as for a ferrocene derivative, as shown by impedance spectroscopy; the kinetics of the heterogeneous electron transfer were shown to be very fast, compared to ferrocene, which makes this new redox site a promising candidate for further studies about molecular wires.

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