S. Quillard

Theoretical and experimental vibrational study of emeraldine in salt form. Part II

We present a complete study of the conductive form of the polyaniline emeraldine salt. The experimental spectra of emeraldine salt doped in the classical way and also by the action of camphorsulfonic acid–m-cresol are presented. Vibrational calculations on emeraldine salt are presented, considering the non-planar geometry of the polymer. A study of the influence of the torsion angle between cycles is proposed. Finally, a complete assignment of the Raman vibrational modes of emeraldine salt is discussed. Copyright

Vibrational spectroscopic studies of the isotope effects in polyaniline

Comparative Raman spectroscopy studies of nondeuterated polyaniline and polyaniline deuterated on the ring and on the nitrogen enabled us to confirm the assignments of principal Raman modes. Spectroelectrochemical studies carried out for these two isotopically different polymers indicate the creation of two types of structures upon electrochemical doping, namely polaron lattice and bipolaronic structure.

Polyanilines and substituted polyanilines: a comparative study of the Raman spectra of leucoemeraldine, emeraldine and pernigraniline

Abstract Raman spectra of the leucoemeraldine, emeraldine and pernigraniline bases have been systematically studied in resonance Raman Scattering with different excitation wavelengths and analysed in details. By using different model compounds, we have made a complete assignement of the Raman and IR vibrational modes. A dynamical calculation based on a valence force-field leads to the determination of force constants between atoms relationship with the nature of chemical bonds, and in particular the aromatic or quinoid character for the benzene rings. The modifications between neutral and protonated emeraldine forms are well interpreted and the role of the electronic distribution around the nitrogen atom is clearly put in evidence. These studies have been extended to the sustituted compound POT (poly-o-toluidine). Based on the above calculations, an assignment is also proposed for Raman modes of the substituted polymer, leading to a clear understanding of the photo-induced IR spectra recorded on the same samples.

Polyaniline containing palladium — new conjugated polymer supported catalysts

Abstract Palladium can be incorporated into polyaniline (PANI) in the polyemeraldine base form via its treatment with PdCl 2 aqueous solutions containing various amounts of HCl. PANI is doped in all the cases, but the oxidation level of palladium introduced into the polymer matrix depends upon the acidity of the PdCl2 solution. After the reaction in highly acidic solutions Pd 2+ is exclusively present in the matrix, whereas upon PANI contact with the solutions of low acidity partial reduction of Pd 2+ to Pd 0 with simultaneous oxidation of the polymer takes place. PANI-Pd systems are active in the catalytic hydrogenation of 2-ethylanthraquinone. Their activity depends on preparation conditions.

Infrared and Raman studies of palladium—nitrogen-containing polymers interactions

In the present research the nature of interactions of poly(4-vinylpyridine) (PVP) and polyaniline (PANI) with various Pd 21 chlorocomplexes existing in PdCl2‐HCl‐H 2O solutions have been studied using IR (MIR, FIR) and Raman spectroscopies. It has been found that these interactions involve the nitrogen atoms of the polymers. In the PdCl 2 solutions of high HCl concentration containing [PdCl4] 22 and [PdCl3(H2O)] 2 as the major species acid‐base type reaction (protonation) with the formation of the polymer salt as well as the coordination of Pd 21 ions by the nitrogen atoms of the polymer take place. In the PdCl2 solutions of low HCl concentration containing [PdCl2(H2O) 2] as the major species protonation proceeds to a small extent. The main process in this case is most probably hydrolysis of the latter with the precipitation of hydrated palladium hydroxide or oxide on the polymer surface. In the case of PANI the oxidation‐reduction between this precipitate and PANI takes place. It results in the oxidation of the polymer chain. q 1999 Elsevier Science B.V. All rights reserved.

RRS characterization of selected oligomers of polyaniline in situ spectroelectrochemical study

Electrochemical, optical and vibrational properties of two oligomeric model compounds of emeraldine salt (ES), the only electrically conducting form of polyaniline, in nonaqueous solution are studied. The phenyl-end-capped dimer and tetramer of leucoemeraldine base are electrochemically oxidized in acetonitrile solution and the electrogenerated species are investigated using spectrophotometry and Resonance Raman Scattering (RRS). In situ resonance Raman study of the oligomers reveals the appearance of the vibrational bands characteristic of the semiquinoid units, and in particular of the CN bond intermediate between the single and double CN bonds which are strongly resonantly enhanced with a red excitation line. The vibrational assignments of the fundamental modes of the electrogenerated species are reported and compared with those of the corresponding polymeric form. Our Raman results provide very interesting information not only about the vibrational properties of emeraldine salt but also about its electronic configuration.

Spectroelectrochemical measurements of the conducting form of polyaniline and related oligomers

Abstract The vibrational features of conducting polymers have proved to be very suitable to characterize the conducting state, since they are directly related to the electronic configuration. We present a vibrational study (experimental measurements and dynamical calculations) of emeraldine salt (ES), the conducting form of polyaniline. In addition, similar analysis is proposed on some oligomers and their corresponding radical forms, chosen as model compounds of ES for our calculations. These results are interpreted in terms of valenceforce-fields, characteristic of the different charged defects.

Preparation and spectroelectrochemical behaviour of a new alternate copolymer of 3,3′-di-n-octyl-2,2′-bithiophene and fluoren-9-one

The synthesis and spectroelectrochemical behaviour of a new solution processible conjugated polymer, namely poly[{5,5′-(3,3′-di-n-octyl-2,2′-bithiophene)}-alt-(2,7-fluoren-9-one)] (abbreviated as PDOBTF), are described. PDOBTF can be considered as the first member of a new family of conjugated copolymers—poly(oligothiophene-alt-fluoren-9-one)s—whose properties can be tuned by changing the length of the oligothiophene segments and their regiochemistry. PDOBTF can be obtained by oxidative polymerisation of 2,7-bis(4-octylthien-2-yl)-fluoren-9-one or by condensation polymerisation of 2,7-bis(5-bromo-4-octylthien-2-yl)-fluoren-9-one using a modification of Yamamoto coupling. Both preparation methods lead to a mixture of polymeric and oligomeric species and require post-polymerisation fractionating if high molecular fractions are to be obtained. Oxidative polymerisation gives product of a higher molecular weight (Mn = 41.0 kDa, Mw/Mn = 1.81 for the highest molecular weight fraction) as compared to the one prepared by Yamamoto condensation polymerisation (Mn = 13.3 kDa, Mw/Mn = 1.45 for the highest molecular weight fraction). Electrochemical oxidation of PDOBTF in an nonaqueous electrolyte (0.1 M Bu4NBF4/acetonitrile) gives rise to an anodic peak at E = 835 mV, which can be ascribed to the p-type doping of the copolymer. The extension of the potential to E = 1500 mV results in the oxidative degradation of the copolymer and induces total loss of its electroactivity. UV-Vis-NIR and Raman spectroelectrochemical data are consistent with the oxidative doping. The latter technique enables the monitoring of the doping-induced changes in both structural sub-units of the copolymer: the bithiophene sub-unit and the fluoren-9-one one.

Vibrational characterisation of a crystallised oligoaniline: a model compound of polyaniline

Abstract We present a detailed study on the vibrational properties of N , N ′-diphenyl-1,4-phenylenediamine in different crystalline forms. A new triclinic form of the molecule has been obtained through appropriate recrystallization procedure. This polymorphism of the crystalline state was associated to different vibrational features. These results are discussed with regards to the possible conformations of the molecule. In order to complete the study, thin solid films of these materials were also elaborated by vacuum sublimation of the molecule, upon selected conditions of rate, deposition and thickness. Spectroscopic measurements of these layers are showed and compared to those obtained on the crystalline solid forms. We performed convenient oxidation processes of this neutral N , N ′-diphenyl-1,4-phenylenediamine (powder and thin solid film) leading to the formation of the correspondent radical cation species. A comparison with radical cation generated in solution by electrochemical oxidative method is done. Vibrational characterisations of this doped oligomer were achieved in each case and finally, the observed differences are discussed in terms of conformation.

Raman and infrared study of phenyl-uncapped oligoanilines

In this paper, Raman and infrared spectra of three completely reduced phenyl-uncapped oligoanilines are presented and discussed. Using suitable dynamic calculations, the set of force constants relative to the primary amine group at the end of one of the two terminal rings was obtained. This study is interesting to understand the vibrational behavior of leucoemeraldine base.