Abstract: This paper deals with different methods for the manufacturing of near-field optical probes with nanometric aperture. After the wet chemical etching of the fiber, two metallization processes are compared: the well-known thermal evaporation versus the novel arrangement of plasma sputtering. Further, it is reported an original controlled nano-indentation in the smooth softness surface to produce the apex aperture of the tapered fiber. These apertures present thin protrusions, but they show good optical and topographic resolutions. Besides, the probe sensitivity is discussed with respect to the multi- and single-mode of the primary optical fiber for imaging sub-wavelength dimension objects in the collection mode. (c) 2007 Published by Elsevier B.V.
Abstract: Microscale fiber tip sensors based on the plasmon resonance are reported. The fabrication process derived from our previous approach for manufacturing near-field scanning optical microscopy probes has been optimized for sensing applications. A typical tip sensor is a tapered fiber 400 mu m in length, coated with a nanoporous thin silver film. The miniaturized geometry of the sensor allows detection in a single droplet of liquid solution (similar to 20 mu l). The tip sensor is sensitive for refractive indices between 1.33 and 1.40 with a sensitivity of at least 3 x 10(-4) refractive index unit (RIU)/nm. The Raman scattering enhancement through these microsensors demonstrates the important role played by the localized plasmon resonance. The sensors' linear response covers a large region, interesting for biosensing in aqueous environments such as biomedical applications. (C) 2007 Optical Society of America.
Abstract: This work presents the manufacturing process of miniaturized SPR sensors using optical fibres. Silver is deposited as a thin layer around the unclad core of a multimode optical fibre. Fibre optic sensors (FOS) are obtained in this way, which have been studied by the modulation of white light. Silver FOS response has been characterized versus different parameters such as the refractive index of the surrounding medium and the film thickness. The response curve of FOS over a significant range of refractive indices shows the known minima shift due to the SPR. Numerical simulation demonstrates that the SPR theoretical curves agree well with experiment. The comparison between numerical and experimental results also allows for the optimization of the physical parameters for the metal film. In order to increase the sensor sensitivity we study the theoretical response of grafting a selective organic transducing biolayer. (C) 2006 Elsevier B.V. All rights reserved.
Abstract: Through numerical simulations supported by an experimental approach, the roughness effects of a gold layer were investigated on the response curves of surface plasmon resonance (SPR) based optical fibre sensors. First, a perturbation term describing the roughness is extracted from the spatial frequency spectrum of the gold surface. This term is then taken into account in the w-k dispersion relationship. Second, an effective dielectric function including the roughness is calculated from experimental data. The response curves were simulated by varying the surface parameters around the experimental ones. The results obtained show that the roughness is a crucial parameter to compare SPR experiments and simulations.
Abstract: A new electroactive polymer has been prepared by oxidative (electrochemical or chemical) polymerization of 3',4'-dioctyloxy-2,2':5',2"-terthiophene. The polymer (PDOTT) is photo luminescent, emitting green light in solution and red light in the solid state. It can be used for the fabrication of organic field effect transistors, however the measured charge carriers mobilities in the transitor configuration (mu = 7x10(-6) cm 2 V-1 s(-1)) are lower than those found for the best polymers reported in the literature. PDOTT is much more promising for electrochemical and electrochromic applications since it shows perfectly reversible spectral response to potential switching. Moreover, in its doped state PDOTT is a strong near infrared absorber.
Abstract: We present detailed voltammetric and spectroelectrochemical studies of poly(2,7-bis(5-[(E)-1,2-bis(3-octylthien-2-yl)ethylene])-fluoren-9-one) (PTVF)-a conjugated polymer consisting of thienylene, vinylene, and fluorenone subunits. PTVF can be easily obtained either by electropolymerization of its monomer ((2,7-bis(5-[(E)-1,2-bis(3-octylthien-2-yl)ethylene])-fluoren-9-one) [TVF]) dissolved in the electrolytic solution or via solid-state electropolymerization of a thin film of the monomer deposited on the electrode. UV-vis-NIR spectroscopic data indicate that the latter method leads to a polymer of a smaller degree of polymerization (DP). The possibility of the formation of a polymeric conductor on a transparent conductive substrate such as indium tin oxide, in situ, via solid-state electropolymerization, combined with its postpolymerization transformation into an organic semiconductor by electrochemical dedoping, is technologically very attractive and makes TVF and its polymer very promising materials for applications in organic electronics.
Abstract: In this paper, we present a study on the porous silicon surface with the aim of filling porous silicon layers with organics. We discuss on two processes used to remove the outer parasitic layer created during the porous silicon formation. We demonstrate that these etching processes influences the surface properties, in particular wetting ability. By XPS and infrared absorption spectroscopy studies, we show that a SF6 plasma treatment does not modify irreversibly the chemistry of porous silicon surface, nor the surface morphology. We also point out that NaOH etching does bring significant morphological modifications and influences the hydrophilicity of the porous silicon surface. This last treatment increases the polar groups (Si-O) concentration on the pore surface and therefore allows a better filling of a porous silicon layer with organics, like dibromo-EDOT which can be thermally converted into PEDOT. (c) 2007 Elsevier B.V All rights reserved.
Abstract: Optical emission resulting from sputtered species during ion bombardment of porous and oxidized porous silicon targets has been studied. Samples were bombarded with 5-keV Kr+ ions at an incidence angle of 70 degrees, and the light emitted was analyzed over the wavelength range 200-300 nm. The surface morphology was investigated, and the micrographs revealed grooves parallel to the plane of incidence when the porosity was surprisingly observed in the grooves under each pore. The results are discussed as a function of the incidence angle and the porosity of the silicon targets.
Abstract: This article reports a new approach for probe manufacturing, which is the key component in scanning near-field optical microscope (SNOM). The wet-etching process, to create the tip at the apex of a tapered fiber, has been optimized. Typical tip features are short tapers, large cone angles (30 degrees), and very small diameters (< 50 nm). Next process steps are performed in an original arrangement of plasma device, based on a modified hollow cathode discharge. It is used for both, to remove the dust particles or the etching residues from the tip surface and to coat the tapered region with a metallic ultrathin and compact film. To complete the probe's fabrication, the tips are opened by dry electrolytic erosion. These probes have been successfully tested for SNOM applications. (c) 2006 American Institute of Physics.
Abstract: Vanadium oxide/polyaniline nanotubes were produced by cationic exchange between hexadecylamine and polyaniline after the synthesis of vanadium oxide nanotubes by sol-gel method followed by hydrothermal treatment. The local structure of this hybrid material was studied by high-resolution transmission electron microscopy, infrared and Raman spectroscopy and small angle X-ray diffraction technique. The results show that polyaniline is intercalated in the interlamellar space of the vanadium oxide nanotube forming a hybrid material with defined morphology. Electrochemical impedance spectroscopy experiments have shown that the apparent diffusion coefficient for nanotubes with template was approximately 1 X 10(-9) cm(2) s(-1). Nanotubes with polyaniline presented an apparent diffusion coefficient at least one order in magnitude higher than the parent material "with template", comparable with other vanadium oxide described in the literature, revealing a promising material for utilization as cathode for ion-Li batteries. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: The electrochemical behavior of the N,N'-diphenyl-1,4-phenylenediamine (B3) in acid solution has been investigated by in situ UV-vis and Raman spectroscopies. The electrogenerated species semiquinone form (B3(circle+)) and monoprotonated structure of B3 (B3(+)) have been characterized as the main products of B3 oxidation. The N,N'-diphenyl-1,4-benzoquinonediimine (B2Q1) species has also been characterized in B3 neutral solution and the B3(circle+) proton loss was attributed to proton absence in solution. Finally, a mechanism has been proposed concerning the electron and proton transfer that occurs during the oxidation process. (C) 2005 Elsevier B.V. All rights reserved.
Abstract: The structural characterization of molecules used in the sterilization of blood for transfusions, such as crystal violet (CV), is relevant for understanding the action of these prophylactic drugs. The characterization is feasible by surface enhanced resonance Raman spectroscopy (SERRS) of CV in solution or on surfaces. The limit of detection of CV by SERRS, in the presence of colloidal particles, using 514.5 nm as excitation radiation, was found to be around 1 ppb. The characterization of CV was also made by SERS, by using different active-particles-containing substrates, proving the versatility of this technique for the study of such structures. The results suggest that the controlled production of highly efficient SERS-active substrates may allow qualitative and quantitative analysis, with high sensitivity, with potential applications in medical and environmental fields.
Abstract: The solvatochromic and thermochromic properties of poly(2,5-di-2'-ethylhexyl-p-phenyleneethynylene) have been investigated. While some important changes were observed in UV-vis absorption, calorimetric, and X-ray measurements, temperature-dependent FTIR, Raman, and solid-state NMR spectra did not reveal any significant shift of the peaks associated with the polymer backbone. These results suggest that the chromic effects are not mainly governed by conformational changes of the polymer. From these data and ab initio calculations performed on model compounds, it is believed that the thermochromic transition proceeds from aggregated polymers at room temperature to "free" (weakly interacting) polymer chains at higher temperatures.
Abstract: We have tailored a new composite based on a porous silica matrix and poly (diacetylene-bis(toluenesulfonide)). The filling of the sample was characterized by energy-dispersive X-ray (EDX) and Raman scattering spectroscopies. Raman scattering, in the polarized mode, was used to check the orientation of the macromolecules in the polymer single crystal before using these data to probe the polymer chain orientation inside the nanocomposite. We have found that polymer chains are oriented along the pore axis with a fairly high conjugation length.
Abstract: Electrochemical growth of poly(3-dodecylthiophene) into mono or double layer of porous silicon used as working electrode is described. The polymer content may be optimized by adjustment of the current density even in a double layer with two different porosities leading to structures. such as active optical guides. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: In this work, the strong influence of the anion on both electropolymerization and redox processes of poly(5-amino 1-naphthol) (poly(5-NH2 1-NAP)) is studied by using electrochemical quartz crystal microbalance (ECQM) and atomic force microscopy (AFM). Studies were carried out in the presence of different acid eletrolytic solutions: hydrochloric acid (HCl) and camphorsulphonic acid (HCSA) to investigated the role played by anions taking into account the very different characteristics of chloride and camphorsulfonate anions such as size, ionic mobility, charge/mass ratio, etc. The electropolymerization process of poly(5-amino 1-naphtol) leads to the formation of adherent and electroactive films but the electroactivity depends on the chemical nature of the counter anion used in the electropolymerization and electrochemical studies. Charge compensation during redox processes occurs by mainly the expulsion/insertion of protons from the polymeric matrix during oxidation/reduction but the participation of anions cannot be neglected and it plays a relevant role in film electroactivity. (C) 2003 Elsevier Ltd. All rights reserved.
Abstract: Previous studies on conjugated polymer nanotubules, prepared by the template method, established that improvements in the molecular and supermolecular structure are responsible for the increase in the room temperature conductivity when the diameter decreases. Our study clearly indicates that a more complex situation can result from the confined synthesis of conjugated polymers in nanopores of a template. Nanowires of poly(3,4-ethylenedioxythiophene), a polythiophene derivative, have been prepared by electrochemical synthesis in polycarbonate templates with diameters ranging between 35 and 200 urn. The electrical transport study (down to 1.5 K) shows that the smaller the nanowire diameter, the stronger the insulating behavior. The temperature dependence of the sample resistance ranges between two extremes, a nonthermally activated regime for the PEDOT film close to the metal-insulator transition and a 2D Mott-variable range hopping-like regime for 35-nm nanowires. It is partly related to the doping level, deduced from X-ray photoelectron spectroscopy (XPS) measurements, which is reduced by about a factor of 2 for 35-nm nanowires, in comparison with the film. But this reduced doping level cannot account for the whole electrical effect. Another important result is the evidence of a decrease in the spin/charge ratio when the nanowire diameter goes from 100 to 50 nm as shown by electron spin resonance (ESR). It suggests that the polaron/bipolaron population ratio is modified. This result will also have important consequences for the transport mechanism.
Abstract: Nanofibers of poly(3,4-ethylenedioxythiophene) - PEDOT and polypyrrole - PPy have been prepared using the template method. We present a study of the electronic and mechanical properties of these nanofibers. Strong variations of the estimated conductivity, the resistivity ratio rho(1.5K)/rho(300K) and the elastic modulus are observed when the diameter is reduced from 200nm to 20nm. They are discussed in terms of change in the conformation of the polymer chains and/or doping level due to the confinement.
Abstract: A study of different oxidation states of poly(5-amino-1-naphthol), poly(5-NH(2)1-NAP), in aqueous acid solutions of chloridric and camphorsulfonic acid is presented. Resonant Raman spectroscopy was used as a tool for following structural changes provoked by not only the redox potential but also the anion used in the polymerization or cycling processes. The apparent chemical homogeneity of the films is questioned because the coexistence of different segments, in the polymeric chain, was observed. Raman spectroscopy together with XPS caracterization allows inferring the presence of "polyaniline-like" segments formed from para coupling during polymerization and also "phenazine-like" segments from ortho coupling leading to a ladder structure.
Abstract: The thermochromic transition in regioregular poly(3-(2-methyl-1-butoxy)-4-methylthiophene) was characterized by UV-vis, FTIR, and Raman spectroscopies. The nonplanar yellow form of this polymer can be planarized at room temperature upon treatment with acetone vapor to yield a red polymer film. Upon heating, combined spectroscopic measurements have revealed important irreversible color changes (from red to yellow) between 75 and 95 degreesC induced by both side-chain and main-chain disordering. These measurements, in particular Raman spectroscopy, clearly indicate a significant planar-to-nonplanar conformational transition of the polythiophene backbone during the thermochromic transition.
Abstract: From bowl-like [Ni3P3S12](3-) anions containing DMF-KNiPS4 solutions, metathesis experiments were successfully carried out using bi-charged anisotropic organic species and led to two new amorphous (PPh3-C3H6-PPh3)(0.5)[NiPS4] (I) and (PPh3-C2H2-PPh3)(0.5)[NiPS4] (II) compounds. Thanks to solid state P-31 NMR, Raman and IR spectroscopies, it has been proved that I and II enclose [NiPS4](-) chains. Hence, [Ni3P3S12](3-) discrete entities can rearrange into chains similar to those observed in the pristine KNiPS4 inorganic materials.
Abstract: This contribution describes the synthesis of a hybrid nanocomposite constituted by vanadium oxide/polyaniline (PAni) with an interesting fibrilar morphology. Nanofibers can be obtained as main reaction products of nanocomposite V2O5/PAni and hexadecylamine after hydrothermal treatment. In general, nanocomposite nanofibers present a typical length varying from 1 to 10 mum and a width varying from 15 to 400 nm. Electrochemical experiments have shown a specific capacity of about 150 A h kg(-1) during the 10 initials cycles, revealing a promissory material for utilization as cathode for ion-Li batteries. (C) 2003 Elsevier B.V. All rights reserved.
Abstract: The synthesis, crystal structures, chemical and spectroscopic properties of NaPdPS4, RbPdPS4, and RbPdPS4{Rb0.33P0.4S2.23Ox} are described. NaPdPS4, RbPdPS4, are isostructural and crystallize in the tetragonal system 14/mcm with cell parameters a = 7.3074(8) Angstrom, c = 12.2308(14) Angstrom and a = 8.2954(3) Angstrom, c = 12.2284(4) Angstrom respectively. RbPdPS4{Rb0.33P0.4S2.23Ox} is cubic, space group Pm-3n and a = 12.0042(2) Angstrom. All compounds contain the same 1/infinity[PdPS4](-) chains made of alternating square planar Pd2+ cations and tetrahedral [PS4](3-) anions. RbPdPS4{Rb0.33P0.4S2.23Ox} contains co-crystallized highly disordered molecular species encapsulated within [Rb-8] cubic cavities. Spectroscopic solid state P-31 NMR, infrared and Raman data as well as elemental analysis suggest that these species could be S-n(2-)(n = 3 or 4) anions and possibly cationic [P4S6O](6+) fragments. NaPdPS4 and RbPdPS4 exhibit exfoliative dissolution in polar solvents giving rise to solutions that show signs of complex fluid behavior. (C) 2003 Elsevier Inc. All rights reserved.
Abstract: The structural defects formed along the polymer chain during the electrochemical intercalation of sodium into polyparaphenylene (PPP) were investigated by in situ FT Raman measurements with an excitation wavelength of 1064 nm. Our Raman data are compared with those obtained for PPP and its oligomers intercalated with Na+ ions by chemical ways. The coexistence of polarons and bipolarons is observed in the early stages of the intercalation process. When the doping level increases polarons are transformed to bipolarons, then in the highly intercalated sample (corresponding to a composition close to Na-0.5(C6H4)), bipolarons are the main structural defects. This evolution, which is reversible, is in accordance with the electron spin resonance (ESR) data of PPP intercalated with sodium ions in the same experimental conditions. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: A derivative of polythiophiene: poly(3-dodecylthiophene) (PT 12) has been used to fill electrochemically a porous silicon matrix. The composite, obtained by this way, should have a high third order nonlinear optical coefficient and good mechanical properties. SEM and TEM micrographs were taken after matrix dissolution in NaOH. Columns of polymer with the matrix pore shape show up like fingers. In consideration of the homogeneous filling profile of PT 12 measured by EDX and XPS and the low amount of polymer, we are probably dealing with tubes instead of wires. (C) 2003 Elsevier Science B.V. All rights reserved.
Abstract: Nanofibers of poly(3,4-ethylenedioxythiophene) (PEDOT) have been electrochemically synthesized by the template method and their morphology determined using electron microscopy. A comparative resonant Raman scattering study has been performed on films, bundles of fibers and individual fibers of different diameters. Their temperature dependent transport properties have also been investigated and compared with the case of a PEDOT thin film. The PEDOT is found to be in an insulating state close to the metal-insulator transition. The temperature dependence of the fibers' conductance is larger than for the films, and this variation increases for a smaller fiber diameter. These results suggest that a confining effect on the PEDOT structure occurs during the electrochemical synthesis in the template. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: The Sr1-xLa1+xAl1-xMgxO4 (0 less than or equal to x less than or equal to 0.7) solid solution with the K2NiF4 structure has been prepared by a new "Chimie Douce" route for the first time. The crystal structures have been refined, from X-ray diffraction patterns, in a tetragonal lattice with the I4/mmm space group. The evolution of Raman and infrared spectra as a function of the composition and the excitation wavelength are observed. These results are discussed on the basis of the interatomic distances. An assignment of the Raman and IR spectra is given for all the compositions.
Abstract: The in situ electrochemical doping process of the poly(3,4-ethylenedioxythiophene) (PEDT) has been studied in an aqueous micellar medium by means of optical spectroscopies. The cyclic voltammetry (CV) and optical absorption results were compared with previous ones obtained either in acetonitrile or in water without surfactant. No significant effect of the medium, water or acetonitrile, was found, but the presence or absence of surfactant in water give rise to different doping CVs, especially in the reductive part. Resonant Raman scattering experiments show a behavior of PEDT different from the one in acetonitrile. The doping mechanism we deduced from these results should imply a variation between an "intermediate" electronic conformation of the polymer in the reduced state to a predominant benzenic one during doping. The comparison with our previous results obtained in acetonitrile leads us to think that the reduced PEDT is in fact slightly oxidized by the aqueous medium. (C) 2001 Elsevier Science B.V. All rights reserved.
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. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: We synthesized a derivative of the poly(3,4-ethylenedioxythiophene) containing a pendant alkyl chain that increases its solubility in CHCl3 and THF, Optical and spectroelectrochemical properties are studied, using in situ Raman scattering and optical absorption spectroscopies. In situ Electron Paramagnetic Resonance (EPR) measurements are also reported. The results are compared to those obtained with the parent polymer.
Abstract: Fully undoped oligo(3,4-ethylenedioxythiophene)s have been synthesized from polycondensation of the corresponding dibromomonomer in the presence of a catalytic Ni(0)-based complex in N,N-dimethylacetamide (DMA). HPLC analysis indicated that the material is constituted of three main oligomers which have also been clearly detected by UV-Visible spectroscopy. Due to its partial solubility in DMA, processability is improved compared to the corresponding insoluble polymer and thin films of oligomers can be deposited by evaporation. Electrochemical and electrochromic properties of undoped film have been carried out. Deep purple in its undoped state, the material becomes sky blue in the oxidized form. The mixture of oligomers was characterized by means of Raman scattering, IR absorption and X-Ray dffraction (XRD), and compared to the poly(3,4-ethylenedioxythiophene) obtained by the oxidative route.
Abstract: We present here the synthesis of fully undoped oligo(3,4-ethylenedioxythiophene) by a dehalogenation polycondensation route. Since it is partly soluble, spectroscopic experiments like optical absorption were carried out. The oligomer was studied by means of Raman scattering, IR absorption and X-Ray Diffraction (XRD), and compared to the PEDOT obtained by oxidative way.
Abstract: Spectroelectrochemical properties and electrical resistivity of an alkyl derivative of the poly(3,4-ethylenedioxythiophene), PEDT-C-14 were investigated. The oxidative doping process of this polymer was studied by means of cyclic voltammetry, UV-vis-NIR optical absorption, Raman scattering and Electron Paramagnetic Resonance (EPR). The in situ conductivity on a Pt microelectrode was also monitored. Optical spectroscopies permit to follow the evolution of the different species that are present. Combination of these different techniques leads to the characterisation of the charged species that are induced by doping, and a mechanism of the modification of the electronic structure of PEDT-C-14 is proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: The oxidation of electrochemically grown poly(indole-5-carboxylic-acid) (P5CO2H) and its spectroscopic properties have been studied by in-situ spectroelectrochemical techniques. The purpose of this paper is to characterize the different modifications on the P5CO2H backbone, induced by the electrochemical oxidation in aqueous acidic solution. We have identified, on the basis of Raman spectra, the vibrational modes associated with neutral and oxidized segments of polymer. It was shown that at least three chemically and optically different species (perhaps other products too) are produced in different potential regimes upon oxidation of this polymer. The results obtained also indicate that the molecular properties of this conducting polymer are better revealed by in-situ resonant spectra than by ex-situ infrared and Raman studies. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: Spectroelectrochemical properties of conducting poly(5-cyanoindole) films deposited on indium tin oxide (ITO) and platinum electrodes are investigated using UV-vis and resonant Raman spectroscopies, The transitions from undoped to semi-conducting state of P5CN require the partial oxidation of the polymer to create radical-cations by insertion of charge-neutralizing anions into the polymer. In order to obtain detailed structural information from the vibrational spectra, it is necessary to know the vibrational modes of oxidation-sensitive bands. Vibrational assignments were made on the basis of the results obtained on polyindole and P5CN in acetonitrile solution. The drastic changes in optical absorption and Raman spectra observed at various stage of oxidation were explained by the conversions between at least three different structures. On the basis of the Raman spectra, we have identified the vibrational modes associated with neutral and polaronic segments. The perturbation associated with the coexistence of these polaronic segments has been described as a quinoid structure growing on the expense of the benzoid one, The results obtained indicate that the molecular properties of the conducting polymers at various stages of an oxidation are better revealed by in-situ Raman spectra than by ex-situ studies. (C) 2000 Elsevier Science B.V. All rights reserved.
Abstract: Experimental and theoretical studies of basic forms of polyaniline are presented. Experimental spectra of emeraldine, leucoemeraldine and pernigraniline and their oligomer model compounds (diphenylamine, phenyl-end-capped diner, phenyl-end-capped tetramer, phenyl-end-capped hexamer, imine form of phenyl-end-capped dimer, pernigraniline base phenyl-end-capped tetramer and emeraldine base phenyl-end-capped tetramer) were recorded in N-methyl-2-pyrrolidone solution and in the solid state. The calculations were performed using the valence force field model, A non-planar geometry of the polymers studied was taken into consideration and particular phenylene ring torsions rendering the system non-planar were analyzed, The assignments of the observed modes was made possible by comparison of the calculated and experimentally measured wavenumbers. Copyright (C) 2000 John Wiley & Sons, Ltd.
Abstract: Surface-enhanced Raman scattering (SERS) is a process with origins, electromagnetic and chemical. The electromagnetic enhancement consists of the excitation of surface plasmons in the metallic support of the thin film. With only the electromagnetic enhancement mechanism, the surface spectra should not differ from volume Raman spectra. However, between SERS and volume Raman spectra, there are differences resulting from the chemical reactions taking place at the polymer/metal interface, intermediated by solvent molecules, that finally depend on the types of polymers and metallic supports. Polyaniline (PAN) is an excellent material to emphasize the chemical component of SERS. This is due to its particular structure with a repeating unit that contains two entities at different weights-a reduced state and an oxidized state-that, in turn, react differently with a metallic substrate. SERS spectra depend on the oxidizing properties of the metal surface, which involves an intermediate compound of the types Ag2O and Au2O3 when N-methyl-2-pyrrolidinone is used as the solvent. This article presents new results concerning the surface chemical effects that produce variations of the PAN SERS spectra. The SERS spectra of the PAN emeraldine base (PAN-EB) layered on Au support are characterized by a semiquinoid structure that we believe is induced on the intermediate compound Au2O3. In the presence of H2SO4, the SERS spectra change gradually as the degree of acid protonation doping increases. The SERS spectra of the fully protonated PAN-EB are identical to those obtained on PAN emeraldine salt (PAN-ES) synthesized by cyclic voltammetry in an acid medium and are invariable with the type of metallic support. The SERS spectra show that the emeraldine salt can be partially or totally deprotonated with water or NH4OH. The deprotonation is complete for the Ag support and partial for the Au support. The SERS spectra of the fully protonated PAN-EB are characterized by a double band with maxima at about 1330 and 1370 cm(-1). Although the generation process of positive charge on the macromolecular chain of PAN-EB doped in the presence of (C4H9)(4)NBF4 is similar to that due to protonic acid doping, involving cation addition (C4H9+ or H+ ions, respectively) in SERS spectra, the complex band situated at about 1330-1370 cm(-1) no longer appears. The doping of PAN-EB with FeCl3 produces two polymer cm forms: a salt type characterized by a protonated structure similar to that found for PAN-ES and a base type similar to the leucoemeraldine form. (C) 2000 John Wiley & Sons, Inc.
Abstract: 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 (C) 2000 John Whey & Sons, Ltd.
Abstract: In this paper, optical and vibrational properties of the FeCl3-doped dimer of polyaniline, a model compound of emeraldine salt are presented. This oligomer is synthesized according to the method reported by Zaghal et al.. A complete assignment of the fundamental in-plane Raman and infrared modes (1700-600 cm(-1)) of this oligoaniline is proposed. The observed frequencies of the dark blue microcrystals are compared with those acquired by vibrational calculations based on a valence force field model. To show, by a most efficient way, the evolution of the electronic configuration of the dimer upon doping, the experimental vibrational modes of the doped dimer and its related force constants are compared with those of its fully reduced and oxidized forms. The strongly aromatic and semiquinone-like characters of the rings present in the doped dimer is put in evidence by Resonance Raman Scattering and infrared absorption and confirmed by vibrational calculations. Considering the numerous similarities between the vibrational characteristics of the polymeric chain and its well-defined oligomer, this study also provides useful information about the electronic configuration of the protonated emeraldine, which remains under debate.
Abstract: In this paper, we present Surface Enhanced Raman Scattering (SERS) experiments performed successfully on some conducting polymers and carbon nanotubes deposited in thin films on rough metallic surfaces. The enhancement mechanism in SERS has a twofold origin: electromagnetic and chemical. The electromagnetic enhancement is, however, the dominant mechanism and consists in the excitation of localized and delocalized surface plasmons (SP). The second enhancing mechanism for SERS, not yet convincingly supported by experimental data, is of chemical origin. This mechanism is due to the increase of the polarizability of the molecules on the metal surface under the action of the incident radiation, leading to the formation of new chemical bonds between the molecules and the metal surface. Unfortunately, the experimental data available to argue the presence of a chemical process are scarce and scattered. In this paper, we try to present some details regarding this aspect. In order to do so, we studied poly 3-hexylthiophene (3-PHT) and polyaniline (PAN) as a function of the type of the rough metallic support (Ag, Au or Cu), the oxidization state and thickness of the polymer layer. We studied also carbon single walled nanotubes. Our experiments reveal the existence of a chemical surface effect. The results obtained for 3-PHT show that SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds. The SERS measurements reported here reveal an increase of the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. We observe for the first time by SERS spectroscopy that doping of 3-PHT with FeCl3 leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. The type of the rough metallic support can modify SERS spectra and such an effect is clearly shown for the polyaniline case. No such dependence on metallic support type is observed on the SERS spectra of carbon nanotubes. (C) 1999 Published by Elsevier Science S.A. All rights reserved.
Abstract: We present a 3D vibrational study of the base form of polyaniline : the leucoemeraldine base (LB). Raman spectra have been recorded for leucoemeraldine and model compounds : diphenylamine (DPA) and the NN'-diphenyl-1,4-phenylenediamine (B3 in our notation). An assignment of the observed Raman bands is proposed. In the same way, we present vibrational calculations based on valence-force-field of these different compounds. Theses calculations have been made by considering the 3D character of polyaniline, i.e the effect of the ring torsion.
Abstract: Conformation sensitive bands are found in the sub-800-cm(-1) region of the IR and Raman spectra of an imine-type oligoaniline, 1. This allows the determination of the conformation in the powder sample (obtained by the Zaghal-Shatnawi procedure) to be predominantly nonplanar E; the abundance of the Z conformer with similar energy is about 5%.
Abstract: 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. (C) 1999 Elsevier Science Ltd. All rights reserved.
Abstract: Calculations based on scaled quantum mechanical method (B3LYP/6-31G*) were performed on a prototype unit of pernigraniline (PB), N, N' diphenyl-1,4-benzoquinonediimine (B2Q1). Models with trans (E) and cis (Z), both in planar and non-planar configurations were used. The calculated infrared and Raman spectra were compared with experiments. The results, especially in the 200-600 cm(-1) frequency range show that B2Q1 has a trans configuration with significant non planarity.
Abstract: Poly(2,5-dithienylene-isothianaphthene) and its analogue, deutered on the benzene ring, have been prepared by voltammetric polymerization of the corresponding monomers in Bu4NBF4/acetonitrile solutions. The polymers obtained are electroactive, showing in cyclic voltammograms two oxidation peaks associated with p-type doping and two reduction peaks, originating from the de-doping process. The use of the polymer deuterated selectively on the benzene ring significantly facilitated the interpretation of Raman spectroelectrochemical data, since it allowed for a differentiation between the bands, originating from the benzene ring and those characteristic of the thiophene backbone. Similarly as cyclic voltammetry, Raman spectroelectrochemistry shows that the oxidative doping of the polymer is a two-step process. The spectral changes observed for the first step of the oxidation are consistent with the formation of the quinonoid sequence of bonds upon doping.
Abstract: The electrochemical redox processes of poly(5-cyanoindole) (P5CN) in acidic aqueous solutions were investigated using in situ Raman and optical absorption spectroscopy. Vibrational assignments were made on the basis of the results obtained on polyindole and P5CN in acetonitrile solution. The drastic changes in optical absorption and Raman spectra observed at various oxidation stages were explained by the conversions between at least three different structures.
Abstract: The vibrational properties of poly(3,4-ethylenedioxythiophene) (PEDT) have been studied by means of UV-vis-NIR optical absorption spectroscopy and resonance Raman scattering (RRS) spectroscopy with two excitation lines: green (514 nm) and infrared (1064 nm). The two-step oxidative doping process does not induce a drastic change for the Raman bands, but the changes that occur are clearly evidenced. During doping, new bands appear, indicating a modification of the electronic structure of the polymer. Vibrational calculations were carried out using a symmetrized dynamical matrix model and the results were compared with experimental data, especially in the 1200-1600 cm(-1) range, where the C-alpha=C-beta and C-beta-C-beta Stretching vibrations are active. It appears that PEDT seems to have an intermediate electronic structure, between the quinoid and benzoid structures.
Abstract: Surface-enhanced Raman scattering (SERS) has proved to be an effective technique for studying the structural properties of conducting polymer thin films. The enhancement process has a twofold origin, electromagnetic and chemical, The electromagnetic enhancement, which is the dominant mechanism in SERS generation, consists in the excitation of localized and delocalized surface plasmons (SPs) in the metallic support of the thin film, The Raman emission of the adsorbed molecules on the metal surface (the most efficient being Ag, Au and Cu) is due to the intense evanescent electromagnetic field located at the interface between the metal and the surrounding medium. The second enhancing mechanism for SERS is of chemical origin, involving the formation of new chemical bonds between the molecules and the metal surface, with the polarizability thus becoming considerably higher than that of the free molecules. This mechanism is as a rule accompanied by a metal-molecule or molecule-metal charge transfer, which partly accounts for the success of the SERS studies on conducting polymers. Unfortunately, these studies have revealed that the chemical effects at the polymer-metal interface varied substantially depending on the various types of polymer and metallic support. In this context, polyaniline containing two different entities (a reduced and an oxidized state) in its repeating units exhibits specific alterations in its SERS spectra depending on the type of metallic support. This paper presents new results concerning the structure of emeraldine-base and emeraldine-salt polyaniline thin films deposited on rough Ag and Au supports. The effect on the SERS spectra of the polymer-metal and polymer-ambient interface chemical reactions is also described. The presence of an interface compound depending on the oxidizing properties of the metallic support has a strong influence on the SERS spectra, no matter how the PAN films were deposited on the support (whether by solvent evaporation or by an electrochemical process, i.e. cyclic voltammetry). When an emeraldine base is doped with HSO4- ions, it turns into an emeraldine salt, which exhibits a disordered state in its macromolecular chain, leading to a modified profile of the similar to 1162 cm(-1) Raman line which is associated with the C-H bond of the quinoid ring. The Lorentzian profile is altered by the addition of a Gaussian profile component. For a rough Ag support, the SERS spectra show that the transformation of emeraldine base films into emeraldine salt films is a reversible process, Copyright (C) 1999 John Wiley & Sons, Ltd.
Abstract: After being dispersed in liquid solvents (Ethanol, CHCl3), conducting polymers and singlewalled nanotubes have been deposited on ruguous substrats (Au, Ag, Cu). With FT Raman technique (laser excitation : 1064 nm), we have obtained SERS signal of both conductiong polymers and singlewalled nanotubes. The Raman signals change with substrat and/or solvent, which could be correlated with the size of clusters formed at the surface and then to the deposition mechanism. The main advantage of the >SERS technique will be emphasized in terms of enhancement as a powerful technique to study nanoparticles.
Abstract: We carried out the study of the 3,3-ethylenedioxythiophene (EDT) and its electrochemically synthesized polymer by means of Raman and UV-vis-NIR absorption spectroscopies. We also studied the doping-dedoping process of PEDT with these methods. An assignment of the Raman lines was attempted for both monomer and polymer, and dynamical calculations have been performed to obtain characteristic valence-force-field of these compounds.
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 valence-force-fields, characteristic of the different charged defects.
Abstract: Thin oligomer films have been deposited by thermal evaporation under vacuum. A filament is placed between the evaporation source and the substrate, the temperature of this filament has been used as parameter. It is shown that systematically an ESR signal appears when the filament is heated during the deposition, while their is no signal after evaporation without filament.
Abstract: Terthiophene powder was synthesised following the cross-coupling Grignard reaction. A tungsten crucible with a multiholed cover was used to evaporate the powder under vacuum. A red-hot wolfram filament is placed between the evaporation source and the: substrates. The variations of the properties of the deposited films were studied using the evaporation rate and the filament temperature as parameters, it is shown that there is some activation of the terthiophene by the hot wolfam filament.
Abstract: In this paper, Raman ana infrared spectra or 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.
Abstract: In this paper, a vibrational study (Resonance Raman Scattering and valence-force-field calculations) of some model compounds of polyaniline is presented. Indeed, this model compound approach allows one to obtain some informations about the vibrational properties and consequently about the electronic configurations of the corresponding polymeric forms. By using valence-force-field calculations, three sets of force constants have been obtained, related to the reduced and oxidized units of the base forms of polyaniline and to the emeraldine salt form.
Abstract: In this work, we have used an oligomer model compound approach for the understanding of the vibrational spectra of the principal forms of polyaniline. Selected model compounds have been studied by Raman and infrared (IR) spectroscopies. The observed vibrational bands are assigned to the expected modes, by revealing the relationships between molecules. In a more theoretical part, dynamical calculations on the different model compounds and their related polymers are presented. The use of model compounds allows us to reach better sets of force constants, as soon as we assume that the parameters can be transferred to the polymeric forms. The obtained values of these force constants are discussed in regards to the oxidation state of polyaniline and its corresponding geometrical structure.
Abstract: We present a comparative study of conductive form of polyaniline, i.e, polyemeraldine doped with HCl vapor or with HCSA upon m-cresol vapor. UV-Vis.-nir absorption measurements on polyaniline thin films, vs acid vapors time exposure, have been made. In the same way, Raman spectra have been recorded with different excitation lines from the blue and red ranges to the infrared region. Finally, an assignment of Raman bands observed, is proposed and confirmed by vibrational calculations based on valence-force-field.
Abstract: A new method for the preparation of poly(isothianaphthene) is proposed, namely electropolymerisation of bis(tert-butyldimethylsilyl)isothianaphthene (BTBDMS)ITN. The advantage offered by this method is based on the fact that (BTBDMS)ITN is a stable monomer at ambient conditions whereas unsubstituted isothianaphthene is unstable and must be prepared prior to the polymerisation. Poly(isothianaphthene) (PITN) prepared from (BTBDMS)ITN shows an average polymerisation degree of 20 and spectral and spectroelectrochemical characteristics similar to classical PITN. FT Raman spectroelectrochemical studies show that during oxidative doping PITN undergoes similar changes to poly(alkylthiophenes) and poly(alkoxythiophenes).
Abstract: The emeraldine salt structure, the only conducting form of polyaniline is not well-known. This is why, we have carried out resonance Raman spectra (RRS) on one of these models compounds oxidized electrochemically in-situ in order to elucidate the electronic structure of this polymer partially oxidized in an acidic medium. A phenyl end-capped dimer of polyaniline, N,N' diphenyl-p-phenylenediamine (named PCD), was selected. This dimer has been electrochemically oxidized in acetonitrile containing 0,2 M tetrabutylammonium tetrafluoroborate as ground salt and 0.1 M diphenyl phosphate as acid. The choice of laser excitation wavelength was fixed by UV-Vis absorption measurements on PCD in the acidic medium. Numerous similarities between emeraldine salt and radical species created were observed and are discussed in this paper.
Abstract: 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.
Abstract: We present a comparative study of conductive salt of polyaniline, i.e., polyemeraldine doped with HCl vapor or with HCSA upon m-cresol vapor. Raman scattering, UV-Vis-nir absorption and conductivity measurements vs acid vapor time exposure have been made. In fact, interesting and similar results have been observed by UV-Vis-nir on thin film of polyemeraldine base doped with HCl vapor [1] and on PANI-HCSA thin films deposited from chloroform and exposed to m-cresol vapor [2]. Raman spectra were recorded with the excitation lines from the blue range (lambda(exc) = 457.9 nm) to the red region (lambda(exc) = 676.4 nm). As expected, results are clearly affected during both processes. These modifications can be interpreted in terms of electronic and conformational changes of the chains, consistent with an increase of the conjugation length and of the delocalization of polarons.
Abstract: In this work, we present a characterization study of the electronic and vibrational properties of regioregular poly(3-decylthiophene) by means of luminescence, optical absorption and Resonant Raman Scattering (RRS) measurements. Photoluminescence studies carried out with an excitation wavelength of 2.42 eV (514.5 nm) show a luminescence signal characterized by a structured band with a maximum at 2.66 eV. Results obtained by RRS are presented and discussed. By using a dynamical model based on a valence force field. Raman vibrational modes are assigned and a set of force constants is determined for the polymer.
Abstract: Poly(3-octylthiophene) was used as a negative resist in e-beam microlithography. This conducting polymer fulfills the main requirements placed on materials which can be useful in this type of process. However, chemical modifications leading to crosslinking are not clearly established at this time. Approach of a mechanism is proposed in this paper which is supported by spectroscopic results obtained from the irradiated materials: it seems reasonable that crosslinking might occur between lateral alkyl groups eventually on carbon atoms in allylic position with the formation of a carbon - carbon double bond between locally stacked Poly(3-octylthiophene) chains.
Abstract: Spectroelectrochemical behaviour of regioregular poly(3-octylthiophene) has been investigated using UV-VIS-NIR and Raman spectroscopies. Static and dynamic UV-VIS-NIR spectroelectrochemical experiments combined with cyclic voltammetry show that oxidative doping of the regioregular polymer is a two-step process in which polarons (radical cations) are first created which then recombine to bipolarons (dications). This two-step oxidative doping mechanism is corroborated by FT Raman spectroelectrochemical studies which show significant changes in the positions and intensities of the Raman bands coinciding with the first and second oxidation peaks in cyclic voltammetry. These changes can be interpreted in terms of the doping induced formation of quinoid sequence of bands in the oxidized polymer. Vibrational calculations carried out for undoped and doped poly(3-octylthiophene) gave a very good agreement between the calculated Raman band frequencies and those recorded experimentally for the regioregular polymer.
Abstract: The effect of polyaniline deuteration on the Raman spectra of this polymer has been studied in detail. Four types of samples have been prepared: nondeuterated polyaniline, polyaniline deuterated selectively on the ring, polyaniline deuterated selectively on nitrogen, and polyaniline deuterated both on the ring and on the nitrogen. Selective deuteration allowed for experimental verification of the Raman modes assignment proposed for different types of polyaniline. In particular, the contribution of C-H bending to C-C stretchings in benzoid and quinoid rings of the polyaniline chain has been confirmed. In addition, selective deuteration enabled us to identify, for the first time in polyaniline, the band associated with N-H bending deformations. Raman spectroelectrochemical investigations of the four above-mentioned types of polyaniline samples gave evidence that in protonated polyemeraldine two types of structures coexist, namely, semiquinone radical cation (polaronic lattice) and quinoid dication (bipolaronic). The vibrations of the former are in resonance with the energy of the blue (457.9 nm) excitation line, whereas the vibrations of the latter undergo resonance enhancement if the red (676.4 nm) line is used. The calculated and experimentally observed Raman modes for both polaronic and bipolaron structures are in very good agreement in all four cases of differently deuterated polyaniline.
Abstract: Raman spectra of neutral and electrochemically doped regioregular poly(3-decylthiophene) were studied using different excitation lines, namely, 457.9, 514.5, 676, and 1064 nm. Contrary to the case of nonregioregular poly(3-decylthiophene) obtained by polymerization with FeCl3, in regioregular polymer the position of the principal band (due to the C-alpha=C-beta stretchings) is essentially independent of the excitation wavelength, proving its high structural homogeneity and extended conjugation. Raman spectroelectrochemical studies of oxidative doping of regioregular poly(3-decylthiophene) can be clearly correlated with cyclic voltammetry and UV-visible-near-IR spectroelectrochemistry provided that appropriate excitation wavelengths are selected. In particular, the use of the red (676.4 nm) and near-IR (1064 nm) excitation lines enables us to register the doping induced changes in the Raman spectra, whereas the green (514.5 nm) line always reveals the vibrations from the undoped segments of the polymer chain independently of the doping level. Finally, vibrational calculations, based on the symmetrized dynamical matrix, performed for undoped and doped poly(3-decylthiophene) led to a good agreement between the calculated and experimentally observed frequencies.
Abstract: In this work, we present an ''in-situ'' spectroelectrochemical study by Raman Resonance Spectroscopy of polyaniline in non aqueous medium with acid or not. By this choice of solvant, we obtained the fully oxidised form (pernigraniline) and we can characterize, in non acidified medium, the oxidative process of the doping. Both 458 and 1064 nm were used in order to get informations by the resonance phenomena of this polymer.
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 assignment 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 in 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.
Abstract: Spectroelectrochemical behavior of polyaniline in nonaqueous electrolytes has been studied by Raman spectroscopy using two excitation Lines: blue (457 nm) and infrared (1064 nm). It has been demonstrated that in the electrolytic solution consisting of tetrabutylammonium tetrafluoroborate/diphenyl phosphate/acetonitrile both oxidation processes (oxidation of leucoemeraldine to emeraldine and emeraldine to pernigraniline) can be investigated by Raman spectroscopy. The blue excitation line is very insensitive to the oxidation and protonation changes occurring during the first oxidation process and reveals only the reduced segments of polyaniline chains. However in the second oxidation process significant changes in the Raman spectra occur, consistent with the formation of pernigraniline units accompanied by deprotonation of the polymer. No Raman spectrum can be recorded for the most reduced form of polyaniline using the infrared excitation line. However gradual oxidation of the polymer results in the appearance of the Raman bands characteristic of the oxidized units which are strongly resonantly enhanced. The infrared Line is extremely sensitive toward the existence of protonated segments and allows for direct monitoring of the deprotonation processes occurring during the second oxidation process (i.e. the oxidation of emeraldine to pernigraniline).
Abstract: We present a comparative Raman study of conductive salt form of polyaniline (i.e. emeraldine salt) doped by HCSA and obtained from a chloroform solution or from a m-cresol solution. In fact, m-cresol solvant is known to induced conformational changes (secondary doping effect) in the case of doped polyaniline. As already observed in conductivity, viscosity and crystallinity measurements, optical and vibrational properties are clearly affected during the secondary doping process.
Abstract: Spectroelectrochemical studies of polyaniline were carried out in aqueous solution by means of UV-vis-NIR absorption and resonance Raman scattering. Raman spectra of the samples polarized from -150 to +650 mV vs SCE have been recorded. It has been found that during an electrochemical cycle, the different resonance conditions strongly influence the resulting Raman data. In particular, the blue (458 nm) excitation line leads to spectra which are very insensitive to the oxidation and protonation state of polyaniline and therefore characterize the reduced state of the polymer. In contrast, both red (676 nm) and near-infrared (1064 nm) excitation lines strongly enhance the spectral features associated with the presence of oxidized (quinoid) units. In addition, FT Raman spectra exhibit new vibrational features which are not observed with other excitation lines. Spectral changes in FT Raman occuring during the increase of the polarization potential are consistent with the protonation induced by oxidation via a semi-quinone radical mechanism. For excitation lines in the visible range (488 and 514 nm), gradual changes can be observed in the Raman spectra as a function of the increasing potential. These modifications are clearly correlated with the increasing oxidation and the protonation of the polymer.
Abstract: Vibrational properties of a series of individual pi-conjugated alpha-coupled oligothiophenes alpha-nT have been investigated by resonance raman scattering (RRS) and infrared absorption spectroscopies. The experimental frequencies obtained on crystalline evaporated alpha-nT (n = 4, 6, and 8 thiophene rings) thin films are compared with those calculated using a symmetrized dynamical matrix model. Special attention is given to the 1300-1600 cm(-1) region where the C-alpha=C-beta and C-beta-C-beta stretching vibrations are active. Also, vibrational spectra of doped alpha-sexithiophene in the solid state are reported where we observe remarkable changes when using different excitation wavelengths. It appears that upon doping, the alpha-sexithiophene polymerizes and the consequent doped poly(sexithiophene) presents a distorted conformation around the inter-ring single bonds. In addition to a complete assignment of the various vibrational modes of each alpha-nT molecule, our results on well-defined model oligomers shed some light on the controversial parent polythiophene and poly(3-alkylthiophenes).
Abstract: In this work, we present a complete vibrational study of a series of the alpha-coupled oligothiophenes. Both experimental and theoretical investigations have been carried out by using spectroscopic techniques such as Raman Scattering and infrared absorption and analysed as a function of the oligomer length. Detailed calculations lead to a clear assignment of the vibrational modes in all compounds and to determination of a main force constants associated with the different chemical bonds. In a similar way, Raman studies of model compounds of poly(thienylene vinylene) (PTV), such as 1-2 bis (thienylene) vinylene (2TV) and 2-5 bis (2-thienyl vinyl) thiophene (3T2V) have been carried out. The two modes associated with the C=C stretching of the vinyl group and the thiophene ring respectively are found to slightly depend on the length of the compounds.
Abstract: Raman ''in situ'' spectroelectrochemical studies have been carried out in order to elucidate the electrochemical doping of poly(3,3'-dibutoxy-2,2'-bithiophene). Raman spectra registered at different potentials strongly depend on the position of the excitation line with respect to the electronic spectrum of the polymer. In particular, blue (458 nn) and red (676 nm) excitation lines are very insensitive toward the oxidative doping of the polymer and independently of the electrode potential always give spectra characteristic of the unoxidized segments of the chain. To the contrary, the infrared excitation line (1064 nm) allows for detailed monitoring of the oxidative doping. The changes in the spectra occurring upon increasing potential of the electrode are consistent with the doping-induced transformation to the quinoid structure. The proposed assignments of the observed Raman bands have been confirmed by the vibrational analysis involving the calculation of the force field and frequencies via Fourier's dynamical matrix.
Abstract: Spectroelectrochemical studies of polyaniline and poly(o-toluidine) were carried out in 1M HCl aqueous solution. Uv-vis-nir and Raman scattering were used during electrochemical oxidation and protonation. The spectra of electrochemically prepared film were recorded for different electrode polarisation potentials. It has been found that resonant conditions which are being constantly changed during electrochemical cycling strongly influence the resulting Raman spectra. Based on previous calculations, an assignment of Raman vibrational modes in poly(o-toluidine) is proposed. The results clearly show that due to symmetry reasons selected vibrational modes in poly(o-toluidine) remain Raman inactive.
Abstract: Protonation of polyaniline with bis(2-ethylhexyl) hydrogen phosphate leads to its plastification. Plasticized polyaniline can be, in turn, thermally processed, which is very important from a technological point of view. Using W-Vis-NIR and Raman spectroscopies we have demonstrated that plasticized polyaniline is effectively protonated with the ester. Raman studies, using different excitation lines (from blue (457.9 nm) to near-infrared (1064 nm)), of polyaniline protonated with bis(2-ethylhexyl) hydrogen phosphate are presented.
Abstract: We present uv-vis and Raman spectroelectrochemical studies of poly(o-toluidine), the simplest ring substituted derivative of polyaniline. The spectra of electrochemically prepared poly(o-toluidine) film were recorded for different electrode polarisation potentials. Based on previous calculations, an assignement of Raman vibrational modes in poly(o-toluidine) is proposed. The results clearly show that due to symmetry reasons selected vibrational modes in poly(o-toluidine) remain Raman inactive.
Abstract: Films of poly(p-phenylene) have been synthesized by electrochemical oxidation of benzene dissolved in ketyl pyridinium chloride-AlCl3 (1:2) melting salt. These films have been characterized from X-ray photoelectron, Raman, photoluminescence and FT-IR spectroscopies. A small amount of residual chlorine is detected from XPS experiments. The shape and strong intensity of the extrinsic part of the photoluminescence (2.0 eV) can be related to a large amount of structural defects in the films; however, the distribution of these defects is relatively homogeneous. Raman spectra clearly show the presence of segments with small conjugation lengths in the films under consideration. Finally, FT-IR spectra reveal that the degree of polymerization is smaller (N(dp) = 15) than those reported (N(dp) = 30) for electrochemical oxidation of benzene in SO2 at low temperature. These results suggest that the films obtained by this new method present some similarities with 'Kovacic compounds'.
Abstract: Electrochemical doping of new soluble conducting polymers, namely, poly(4,4'-dialkyl-2,2'-bithiophenes), has been studied 'in situ' and 'ex situ' by various spectroscopic methods. These compounds represent the 'head-to-head' and 'tail-to-tail' analogues of poly(3-alkylthiophenes). The pi-->pi* transition in poly(4,4'-dialkyl-2,2'-bithiophenes) is blue shifted with respect to that characteristic of poly(3-alkylthiophenes) suggesting a higher torsion angle between the adjacent substituted thiophene rings. The doping-induced bipolaronic bands (Vis-NIR) are, however, located in essentially the same positions as the doping-induced ones in poly(3-alkylthiophenes). This observation may suggest that during doping, more twisted poly(4,4'-dialky1-2,2'-bithiophenes) adopt a structure more similar to that of doped poly(3-alkylthiophenes). The changes in FT-IR spectra are also consistent with the bipolaron model since all the five expected doping-induced modes appear with the onset of the oxidation peak and grow in intensity with increasing potential.
Abstract: In this paper, we present dynamic calculations of vibrational modes of two forms of polyaniline : the fully reduced form (Leucoemeraldine Base) and the fully oxidized form (Pernigraniline Base). Our model is based on the use of force constants to provide an interpretation of experimental frequencies obtained by Resonant Raman Scattering and infrared absorption. In order to obtain the best set of parameters, we have performed calculations on both polymers and model compounds. Our model leads to a good fit between experimental and calculated frequencies, also we present the main force constants which are in agreement with previous works performed on similar aromatic structures.
Abstract: In this work, we present a characterization study of the electronic and vibrational properties of parasexiphenyl by means of luminescence, optical absorption and Resonant Raman Scattering (RRS) measurements. Both undoped and p-doped compounds have been investigated. The oxidation of a thin film of parasexiphenyl by AsF5 was followed by Raman Scattering and UV-visible absorption measurement. Optical absorption spectra show localized states within the gap at 1.25 and 3 eV, signature of bipolarons. Photoluminescence studies carried out with an excitation wavelength at 3,06 eV Which is 406.7 nm show only an intrinsic luminescence signal which strongly decreases in intensity with doping and characterized by a structured band with a maximum at 2.66 eV. Finally, we present and discuss results obtained in RRS after doping. By using a dynamical model based on valence force field, we show that the modifications are consistent with the presence of a quinoid structure along the chains.
Abstract: In this paper, we present a study of vibrational properties of conducting polymers containing thiophene rings : polythiophene and polyalkylthiophenes. The spectrocopic studies include Resonance Raman Scattering (RRS) and Fourier Transformed InfraRed absorption (FTIR), that we applied to the polymers mentionned above and to some thiophene oligomers. Results are interpreted by performing dynamical calculations based on a valence force field model. With the oligomer approach, the force constants are less numerous than the experimental frequencies and the results for our assignment much more reliable. The calculations provide a better understanding of Raman and infrared modes, leading to a clear comparaison of the electronic and vibrational properties of neutral polythiophene, polymethylthiophene and polyoctylthiophene.
Abstract: We report spectroscopic studies (RRS and FTIR) of some thiophene oligomers, polythiophene and polyalkylthiophenes. The polymers have been synthetized from thiophene, 2.2'-bithiophene, methylthiophene and octhylthiophene respectively. The vibrational results are interpreted by dynamical calculations based on a valence force field model. A complete set of force constants is obtained and compared to those found in other compounds (1). These calculations provide a better understanding of the vibrational properties. Particulary, the Raman modes at 1498, 1365 and 700 cm-1 in polythiophene are completely assigned. In order to understanding the conducting properties of these polymers, we have doped polythiophene and we propose an interpretation of the new spectrum, in terms of changes occurring in the determination of some force constants.
Abstract: The study of parasexiphenyl thin films deposited under vacuum indicate that deposition parameters - such as evaporation rate, substrate temperature - play a major role. Here we show that the best cristallinity is obtained with a high substrate temperature and a very low evaporation rate. A texture shows up under these experimental conditions, the axis of the parasexiphenyl molecules being normally to the substrate surface.
Abstract: In this paper, we present Raman and Infrared spectra of two forms of polyaniline: the fully reduced form (called leucoemeraldine base) and the fully oxydized form (called pernigraniline base). Dynamic calculations based on a valence-force-field model have also been carried out on these two polymers and some model compounds, to give a clear interpretation of vibrational observed modes. We have obtained a good fit between experimental and observed frequencies. Our set of force constants are physically reasonable compared to parameters found in other aromatic compounds.
Abstract: We report studies carried out experimentally and theoretically on a series of poly(arylene vinylene)s: PPV, PTV and PFV. Raman and infrared spectra are described and analyzed in the frame of a dynamical model based on valence-force-field calculations. In order to achieve good fits and to obtain reasonable sets of force constants, we have used different series of model compounds, such as trans-stilbene and distyryl-benzene in the case of PPV, and thiophene, trans-bis(2-thienyl)ethylene (TTE) in the case of PTV. It tums out that such compounds are necessary to obtain consistent results. In the case of PTV, for example, we found from calculations that an assignment slightly different from the one proposed in the literature has to be considered concerning the C-C stretching mode of the thiophene ring. An extension of these results to PFV leads to a good assignment of both IR and Raman modes in agreement with experimental data.
Abstract: Extensive studies have been carried out on the different forms of polyaniline. In this paper, we present a study of the vibrational properties of the leucoemeraldine base, the reduced form of polyaniline. Infrared absorption and resonant Raman scattering (RRS) spectra are presented for the polymer, together with those obtained in model compounds such as diphenylamine and N,N'-diphenyl-1,4-phenylenediamine. The Raman spectrum of the leucoemeraldine base exhibits mainly bands at 1181, 1219, 1597 and 1618 cm-1. By the use of a valence-force-field model, we have assigned these vibrational modes, including those of the model compounds. Calculations are in rather good agreement with previous assignments and the main force constants, which are determined from the fit of the experimental IR and Raman bands, are physically reasonable compared to what is found in other polymers.
Abstract: The oxidation of parasexiphenyl thin films was followed by U.V.-visible absorption spectrometry. Localized states are created within the gap whose signature shows up as two new absorptions centered at 3 eV and 1,25 eV. A quinoid structure is evidenced by Raman scattering and I.R. absorption which furthermore disappears after compensation under our experimental conditions.
Abstract: In this work, we present a characterization study of PPP prepared in the form of polycristalline thin films, via a precursor polymer route. U.V. visible absorption spectra exhibit a main peak at 3.65 eV. Photoluminescence studies carried out with an excitation wavelength at 406 nm show different components assigned to intrinsic photoluminescence superposed to an extrinsic contribution due to structural defects. In Resonance Raman Scattering (RRS), by excitation in the near U.V. range range (351.1 nm), the bands peaked at 1220, 1280 and 1600 cm-1 are similar to those observed in standard PPP synthetized by other methods.
