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Conjugated phenylene-vinylene polymers are widely used in organic light-emitting and photovoltaic devices. The comprehension of the optical properties upon charge injection is of crucial importance for the improvement of such organoelectronic devices. The processes of electrochemical doping, electrolyte diffusion, and degradation have been studied by cyclic voltammetry and chronoamperometric methods. Kinetic studies by in situ fluorescence spectroscopy have been used for the determination of the mobility of charge carriers in the polymer making used of electrochemical Stern-Volmer analysis. The mobility of holes for MDMO-PPV measured by this method was 2.5 x 10(-7) cm2 V s(-1). Non-Faradic variations of the fluorescence after doping-dedoping cycles have been related to morphological changes in the polymeric layer. The evolution of the fluorescence obeys a first-order kinetics law, similarly to the trend of the variation of volume during gel shrinking.

Abstract: A potentiostatic method has been employed to obtain silica layers on the surface of glassy carbon electrodes from a precursor sol–gel solution. The silica-modified electrodes were then used as a porous matrix for the electrochemical growth of conducting polyaniline. As a result, the overall synthesis of an organic–inorganic nanohybrid material has been achieved only by electrochemical methods. The growth of polyaniline is, in the first step, confined inside the silica matrix and appears to be controlled by the diffusion of aniline monomer units. Later, once the polyaniline fibers have reached enough length, emerge out of the template and the growth kinetics becomes comparable to that for polyaniline synthesized on a bare electrode. The silica matrix has a positive effect on the electrical capacitance of Pani since the polymer chains grow dispersed and the collapse between them is minimized. [Copyright &y& Elsevier]

The electrochemical behaviour of benzene on platinum electrodes (polycrystalline and single-crystal electrodes) has been studied in acidic and alkaline solutions. In acid solutions the reduction of benzene to cyclohexane takes place in all the platinum surface structure employed, however it does not occur in alkaline media (0.1 M NaOH). In this case, the hydrogen adsorption–desorption processes displace the adsorbed benzene from the electrode surface. The oxidation of benzene is also affected by the pH of the electrolyte and also by the surface structure of the platinum electrode used. In acid solutions, this oxidation at higher potentials (1.4 V vs. RHE) yields CO2, benzoquinone and α,β-unsaturated esters or lactones, however in alkaline media carbonate anions coming from CO2 and salts of carboxylic acids have been detected by in situ FTIR spectroscopy using a platinum polycrystalline electrode. Bulk electrolysis of benzene solutions using a platinum electrode in acid and alkaline media was performed in order to confirm the results obtained by spectroscopic measurements. [Copyright &y& Elsevier]

In the present work, the electrochemical properties of single-walled carbon nanotube buckypapers (BPs) were examined in terms of carbon nanotubes nature and preparation conditions. The performance of the different free-standing single wall carbon nanotube sheets was evaluated via cyclic voltammetry of several redox probes in aqueous electrolyte. Significant differences are observed in the electron transfer kinetics of the buckypaper-modified electrodes for both the outer- and inner-sphere redox systems. These differences can be ascribed to the nature of the carbon nanotubes (nanotube diameter, chirality and aspect ratio), surface oxidation degree and type of functionalities. In the case of dopamine, ferrocene/ferrocenium, and quinone/hydroquinone redox systems the voltammetric response should be thought as a complex contribution of different tips and sidewall domains which act as mediators for the electron transfer between the adsorbate species and the molecules in solution. In the other redox systems only nanotube ends are active sites for the electron transfer. It is also interesting to point out that a higher electroactive surface area not always lead to an improvement in the electron transfer rate of various redox systems. In addition, the current densities produced by the redox reactions studied here are high enough to ensure a proper electrochemical signal, which enables the use of BPs in sensing devices. [ABSTRACT FROM AUTHOR]

Highlights • Electrochemical synthesis of self-doped polyaniline derivatized with carboxylic acid groups. • in situ FTIR characterization and XPS spectra demonstrate the incorporation of self-doping moieties. • Poly(Aniline-co-aminoterephtalic acid) presents electroactivity at neutral pH. Abstract The electrochemical copolymerization of aminoterephthalic acid and aniline can be achieved to yield a self-doped material showing electroactivity at physiological pH. The present study focusses on the management of the synthesis conditions to obtain a true copolymerization product and to control the relative amount of both comonomers eventually incorporated to the copolymer chain. Both, in situ FTIR spectroscopy and ex situ XPS techniques proved the successful incorporation of aminoterephthalic acid and, in parallel to other polyaniline parent derivatives, revealed the existence of redox transformations involving leucoemeraldine-emeraldine-pernigraniline transitions. The use of a high inversion potential (1.4 V/RHE) during electro-copolymerization resulted in a material enriched in aminoterephthalic acid fraction with respect to aniline, while this last component is favored at lower potentials. The pH behavior of copolymers in combination with in situ FTIR results strongly suggested that a larger content of aminoterephthalic acid (such as that obtained after deposition at 1.4 V) do not ensure an extensive self-doping process because a significant fraction of those carboxylic moieties remain inactive during the redox transformation. Instead, low inversion potentials are preferred to obtain a material with less defects and thoroughly electroactive at physiological pH. [ABSTRACT FROM AUTHOR]

Poly(2-amino-4-tert-butylphenol), poly(2A-4TBP), was synthesized from monomer aqueous solution using either electrochemical or chemical oxidation procedures. Several spectroscopic characterization techniques were employed to gain information on the chemical structure and redox behavior of the obtained materials. It was found that the chemical polymerization product could be described as an oligomer mixture containing up to 16 monomer units. In parallel to other polymers derived from o -aminophenol, phenoxazine rings constitute also the basic structure of poly(2A-4TBP). In addition, the occurrence of N-N couplings, which are favored by the presence of the voluminous tert -butyl substituent, seems also relevant. No significant structural differences were found between the chemically or electrochemically synthesized materials. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study about the influence of the thickness of electrochemically deposited polyaniline (PANI), used as hole-transporting layer, on the behaviour of polymer light emitting diodes is presented. Two sets of devices with a different conjugated polymer used as active layer were prepared. Poly(9-vinylcarbazole) was used for the first type of devices, whereas Poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene] was used for the second type. Each set consists of five polymeric diodes in which the hole-transporting layer has been varied. In one case of each set no layer was deposited, in other one a Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) layer was deposited, and in the rest of the diodes a different thickness of electrochemically deposited PANI was employed. The optic and electronic characterization of the devices show that controlling the thickness of the PANI hole transporting layer, both the maximum emission peak of the electroluminescence curves and the driving voltage could be tuned. Furthermore, an exponential behaviour has been demonstrated for the maximum intensity of the electroluminescence curves as a function of the applied excitation voltage between anode and cathode. [Copyright &y& Elsevier]