Alain Adenier

Electroactive poly(aromatic amine) films for iron protection in sulfate medium

Polyaniline (PANil and poly(1,5-diaminonaphthalene) (PDAN) films can be deposited on iron from aqueous sulfuric acid. The films exhibit electroactive properties similar to those of PANi and PDAN generated on platinum. Electrosynthesis performed in the presence of both monomers leads to a composite film which presents excellent adhesion properties on iron. The composite film imparts a form of anodic protection for at least 9 days in pH 4 sulfate medium.

Polythienobenzothiophenes, a new family of electroactive polymers: electrosynthesis, spectral characterization and modelling

New conducting polymers, including poly[thieno[3,2-b][1]benzothiophene] (poly-TBT) and poly [6-methoxythieno[3,2-b][1]benzothiophene] (poly-MeOTBT) were electrosynthesized by anodic oxidation of the corresponding monomers in 0.1 M LiClO4 acetonitrile solution. Poly-TBT and poly-MeOTBT electroactive films were formed on platinum electrodes and characterized spectroscopically. FT-IR studies show that both polymers present couplings occurring on the thiophene moiety and the phenyl ring, with a step-like structure. MALDI-TOF mass spectrometry indicates that poly-TBT and poly-MeOTBT films are mainly constituted of short-chain oligomers. The results of molecular orbital (MO) calculations performed on the basis of a radical-cation electropolymerization mechanism are in good agreement with our spectral data.

Luminescence Properties of New Fused Benzothiophene Derivatives and Their Conductive Oligomers Structural and Solvent Effects

The structural and solvent effects on the electronic absorption and fluorescence spectra, and fluorescence quantum yields, of four new fused benzothiophene derivatives, including benzothieno[3,2b]-thiophene (BTT), benzothieno[3,2-b]benzothiophene (BTBT), 6-methoxy[1]benzothieno[3,2b]-thiophene (MeOBTT), and benzothieno[3,2-b]indole (BTI) were investigated at 295 K. The luminescence properties of the corresponding conductive oligomers, poly(BTT) and poly (MeOBTT), electrosynthesized in acetonitrile, were also studied. Satisfactory McRae, Suppan, and Kawski-Chamma-Viallet solvatochromic correlations were established for the four monomers in most solvents. A weak negative solvatochromic behavior was found for these compounds, indicating that their dipole moments are slightly lower in the excited singlet state than in the ground state. Kamlet-Abboud-Taft multiparametric correlations were also obtained for absorption and fluorescence wave numbers and quantum yields, demonstrating the existence of specific solute-solvent interactions. In the case of the oligomers, important red-shifts of the fluorescence emission maxima (Δλ ≈ 90–110 nm) relative to the corresponding monomers were observed, which shows the extent of conjugated segments in the oligomer chains.

Macroscopic modulation of the π-electron density of pendant groups grafted on conductive polymers

Abstract The influence of the redox switching reaction of a conductive polymer upon the π electron density of grafted pendant groups has been studied. Poly( N -phenylpyrrole) and poly( N -benzylpyrrole) have been compared by means of IR spectroscopy and molecular modelling. In the case of poly( N -phenylpyrrole), the evolution of the infrared vibrational bands expresses a reversible modulation of the π electron density of the benzene nucleus when the polymer is switched from its reduced to its oxidized form. There is no such effect when the aromatic moieties are separated from the polymer backbone by a CH 2 group. Moreover, molecular modelling suggests that oxidation of poly( N -phenylpyrrole) makes it possible to break the conjugation between the benzene nuclei and the polypyrrole backbone.

Hydrogen bonding and steric effects on rotamerization in 3,4-alkylenedioxy-, 3-alkoxy- and 3,4-dialkoxy-2-thienyldi(tert-butyl)methanols: an NMR, IR and X-ray crystallographic study

The equilibrium constant for the anti ↔ syn rotamerization (anti: intramolecularly hydrogen-bonded hydroxy group; syn: “free” hydroxy group) of 3,4-alkylenedioxy-, 3-alkoxy- and 3,4-dialkoxy-2-thienyldi(tert-butyl)methanols depends on the 3,4-alkylenedioxy or alkoxy group(s) and the solvent, hydrogen-bonding solvents such as DMSO and pyridine favouring the syn isomer. Equilibrium constants ([syn]/[anti]) in chloroform and benzene decrease in the order: 3,4-OCH2O-, 3,4-O(CH2)2O-, 3-OMe, 3-OEt, 3,4-(OMe)2 ≈ 3-Oi-Pr, 3,4-(OEt)2, ranging over about 2.5 orders of magnitude. Variations in the IR OH stretching frequencies and the NMR OH proton shifts for the anti isomer indicate that intramolecular hydrogen bonding increases in roughly the same order. The syn → anti rotation barrier in DMSO increases with substituent size and number. The 3,4-methylenedioxythienyl derivative has a rather lower barrier (17.5 kcal mol−1) than all the others (21.0–22.3 kcal mol−1). The syn → anti rotation barrier is largely determined by steric effects but intramolecular hydrogen bonding in the anti isomer contributes to the variation of the anti → syn rotation barrier. A single crystal X-ray diffraction study of the anti-3,4-diethoxy derivative shows that the orientation of the 3-alkoxy group is very different from that in anti-3-methoxy-2-thienyldi(1-adamantyl)methanol. Molecular mechanics and quantum mechanical calculations are used in an attempt to rationalize the equilibrium data.

Self-association mechanisms in aqueous media: dimerization versus micellization of alkyl-ellipticinium derivatives

Self-association mechanisms in aqueous media of ellipticinium (E), 2-methylellipticinium (2-NME), oxazolopyridocarbazolium (H-OPC), 10-pentyloxazolopyridocarbazolium (10-pentyl-OPC), 2 aminopentyloxazolopyridocarbazolium (2-aminopentyl-OPC) and 2-pentyloxazolopyridocarbazolium (2-pentyl-OPC) acetates have been investigated by spectroscopic and kinetic studies. Whereas E, 2-NME, H-OPC, 10-N-pentyl-OPC and 2-aminopentyl-OPC dimerize by self-stacking, the 2-pentyl-OPC displays micellar behaviour (with a critical micellar concentration of 20 µmol dm–3), as a direct consequence of its amphiphilic character. As regards dimerization, both aliphatic substitution (Kd= 7.6 × 103 and 2.4 × 104 dm3 mol–1 for E and 2-NME, respectively) and extension of the π-electron aromatic system (Kd= 1.4 × 105 and 4.5 × 105 dm3 mol–1 for H-OPC and 10-pentyl-OPC, respectively) significantly increase the dimer stability. From kinetic analysis, dimer stability seems to be controlled mainly by the reverse rate constants which vary from 4.9 × 104 to 1.9 × 103s–1.

Rate and equilibrium effects of tert-alkyl groups on rotamerization in 3,4-alkylenedioxy-, 3-alkoxy- and 3,4-dialkoxy-2-thienyl(di-tert-alkyl)methanols: an IR, NMR, kinetics and MM study

Di-1-adamantyl and (1-adamantyl)(tert-butyl) analogues are compared with the previously studied 3- or 3- and 4-substituted 2-thienyl(di-tert-butyl)methanols. The equilibrium constants for syn–anti rotamerization ([syn]/[anti]) are slightly greater than for the smaller di-tert-butyl derivatives. In the intramolecularly hydrogen-bonded anti rotamers, neither the 1H NMR shift of the hydroxy proton nor the OH stretching frequency, both indicators of intramolecular hydrogen bond strength, is greatly affected by a change in the tert-alkyl group; these changes in the equilibrium constants must, therefore, be attributed to variations in steric effects. The rotation barriers for the compounds with the larger tert-alkyl groups are much enhanced and better differentiated. In all three sets the syn→anti and anti→syn rotation barriers are linearly correlated, and either can be correlated with the free energy difference. Nevertheless, the data do not meet the criteria for a classical Leffler–Grunwald-type rate-equilibrium relationship. Molecular mechanics calculations (MMFF94 force field) account fairly well for the variation in the free energy difference for rotamer pairs of the di-1-adamantyl, (1-adamantyl)(tert-butyl) and di-tert-butyl derivatives, but slightly overestimate the small differences in the equilibrium constants for the three series. The calculated rotation barriers for the di-tert-butyl compounds are about 7 kcal mol−1 higher than those observed. Those for 2-anisyl-, phenyl- and 2-tolyldialkylmethanols are increasingly overestimated as the rotation barrier rises, but a good correlation ranging over 20 kcal mol−1 is obtained; this correlation is not coincident with that for the thiophene derivatives.