Sandro Zecchin

Chemical and electrochemical synthesis and characterization of polydiphenylamine and poly-N-methylaniline

Abstract Chemical and electrochemical oxidation of diphenylamine and N -methylaniline in acid produces polyaniline-like polymers, which can be characterized by elemental analysis, cyclic voltammetry, IR, UV-visible and mass spectroscopy. Diphenylamine undergoes para C-C coupling to oligomers ( n = 3-4), while N -methylaniline couples C-N at the para position, attaining a high degree of polymerization. The conductivity of polydiphenylamine (3 × 10 −2 Ω −1 cm −1 ) increases when polymerization is performed in acetonitrile (0.5 Ω −1 cm −1 ), in which n increases to 10–11. Poly- N -methylaniline has a conductivity of 1 × lO −3 Ω −1 cm −1 . The polymers are oxidized reversibly from the yellow (leuco) to the green form (emeraldine) and finally to the blue (pernigraniline) form in two steps, each involving 0.5 electrons per monomeric unit. With increasing chain length and conductivity, the electrochemical stability of the emeraldine form of polydiphenylamine also increases.

Irreversible processes in the electrochemical reduction of polythiophenes. Chemical modifications of the polymer and charge-trapping phenomena

Abstract Irreversible changes occurring in the electrochemical reduction of some polythiophenes in acetonitrile have been investigated by cyclic voltammetry (CV), UV-Vis and IR spectroscopy and the electrochemical quartz crystal microbalance (EQCM). Reduction in the presence of alkali metal cations (Li + , Na + , K + and Cs + ) does not result in n-doping but in hydrogenation of the alkene moieties. The promotion of double-bond saturation by alkali metal cations following the order Li + , Na + > K + > Cs + is attributed to their charge-pinning action which decreases as the ion radius is increased. Reversible reduction in tetralkylammonium electrolyte (n-doping) is accompanied by production of hydroxide ions within the polymer which are thereby inserted by subsequent oxidation. The resulting quinone-like groups are responsible for the CV pre-peaks usually observed in conducting polymers after n-doping and previously assigned to trapped charges.

Anodic oxidation of triphenylphosphine at a platinum electrode in acetonitrile medium

Summary The electrochemical oxidation of Ph 3 P at a platinum electrode in CH 3 CN solvent has been studied using cyclic voltammetry and controlled potential electrolysis. In the anodic reaction, the triphenylphosphinium cation radical initially produced reacts both with Ph 3 P to form a phosphonium cation and with the trace of water present in the solvent to give triphenylphosphine oxide in a ratio depending on water content. When Ph 3 P is oxidized in presence of benzene tetraphenylphosphonium ion is found. The yield of Ph 4 P + in the electrolytic preparation is not very high because a Ph 3 P portion reacts to give Ph 3 PH + and Ph 3 PO.

Electrochemical synthesis and properties of polycarbazole films in protic acid media

Conductive films are deposited onto Au by anodic oxidation of carbazole dissolved in aqueous alcoholic HClO4. Cyclic voltammetry of film electrodes in aqueous HClO4 prepared in this way shows the occurrence of two main redox processes: an intermediate system becoming less important on cycling is ascribed to dimers or trimers. The polymer is remarkably stable when cycling involves only the first peak, while the second oxidation leads to degradation. An acid environment appears to be essential for film electrochemistry: ESR data confirm that protonation ensures conductivity of the material. On this basis, structure and conduction mechanisms similar to those of emeraldine are suggested.

Electrodeposition of Amorphous Fe2 O 3 Films by Reduction of Iron Perchlorate in Acetonitrile

Electrodeposition of amorphous Fe 2 O 3 films of nanometer size was performed by reduction of Fe(ClO 4 ) 3 or Fe(ClO 4 ) in oxygenate acetonitrile. Cyclic voltammetry has shown that the oxide-film formation occurs via oxidation of electrodeposited metal by dissolved oxygen. The oxide films were characterized by cyclic voltammetry, electrochemical quartz crystal microbalance, X-ray i raction, and UV-visible spectroscopy. The films are reversibly reduced in acetonitrile + LiCIO, in two redox processes to the Fe 3 O 4 and FeO oxides via lithium intercalation. The UV-visible (UV-vis) spectrum displays absorption with an optical gap (1.75 eV) characteristic of amorphous Fe0 3 . Spectroelectrochemistry has shown that reduction causes bleaching of the yellowish films (electrochromic efficiency ≅30 C -1 cm 2 at 400 nm). Heating the films at 500 °C converts them to the crystalline α-Fe 2 O 3 form with loss of electroactivity.

Electrochemistry of coordination compounds XV. Paramagnetic hydrido complexes of cobalt(II), rhodium(II) and iridium(II)☆

Abstract The electrochemical behaviour of a series of d8-hydrido complexes of cobalt, rhodium and iridium containing phosphorus ligands has been studied. The oxidation proceeds in two one-electron steps involving a rare hydrido complex in the II state, which, in the case of rhodium and iridium, is unstable and decays through a disproportionation pathway. An oxidationreduction mechanism accounting for the chemical and electrochemical results is proposed.

Mixed-valence conduction in redox-substituted polythiophenes. Enhancement of redox electron-exchange rate by polyconjugated chains

Abstract The in situ conductivity of some poly(cyclopentadithiophenes) modified at the 4 position with reducible ( p -nitrophenyl and p-N -methylpyridyl) or oxidizable (ferrocene) redox groups was investigated in acetonitrile. In the nitrophenyl- and pyridyl-functionalized polymers the reduction, which is confined to the pendant redox group, makes the polymer mixed-valence conductive. The conductivity ((3–6) × 10 −3 S cm −1 ), which is the highest reported for a redox polymer, remains within the limits expected for a direct intersite electron hopping. In the ferrocene-functionalized polymers the oxidation involves both the redox group and the backbone. Redox conduction at the ferrocene group is enhanced by hopping through the conductive polymer backbone. The hopping rate is increased by a decrease of the ferrocene-backbone distance and by conjugation of ferrocene with the backbone itself making conductivity increase up to 1 S cm −1 .

Electrochemical and chemical synthesis and characterization of sulfonated poly(3,4-ethylenedioxythiophene): A novel water-soluble and highly conductive conjugated oligomer

Electrochemical and chemical polymerization of a 3,4-ethylenedioxythiophene derivative bearing a sulfonate group (EDTS) is reported. The electrochemical polymer, poly(EDTS), which is very soluble in water, has been produced both from acidic, water, resulting in the solution form, and from acetonitrile using additional perchloric acid in 1:1 ratio to the monomer, resulting in the production of polymer films. Both forms were characterized by cyclic voltammetry, UV-Vis spectroscopy, EQCM analysis, MALDI-TOF MS and conductivity measurements, and show high conductivity (0.5-10 S.cm -1 ) and high solubility in water (>10%). Poly(EDTS) was also prepared by chemical polymerization with Fe(OTs) 3 in water to yield once more a water-soluble and conductive (1-5 S.cm -1 ), polymer.

Electrooxidation products of methylindoles: Mechanisms and structures

Electrochemical oxidation of 1-methylindole, 2-methylindole and 3-methylindole on a platinum anode in acetonitrile containing NaClO4 has been studied. In any case no polymeric deposit on the working electrode was obtained. The identification of the obtained soluble products is described and the mechanisms of formation are discussed. Analogously to the case of unsubstituted indole, electrooxidized 1–3 react through positions 2 and 3. The non polymerization of 1 is explained with the formation of a tetramer which is oxidized to a stable radical cation and dication without undergoing further coupling reactions.

The reversible hydroxide doping of polypyrrole. Delay of polaron and mobile bipolaron injection in polypyrrole by H bonding of hydroxide anions

Abstract The reversible hydroxide-anion doping of polypyrrole (PPy) has been investigated by FT-IR, cyclic voltammetry, in situ conductivity and ESR techniques. FT-IR confirmed that the hydroxide anion substitutes the counteranion reversibly in doped PPy. The dopant hydroxide anion produces a strong negative shift of the oxidation potential of PPy and doubling of the reversible charge. No similar effects are displayed in N -substituted PPys. In situ conductivity shows that the material becomes conducting (up to 2 S cm −1 ) only after about 50% of the doping charge is passed. Similarly, the ESR signal is absent during the initial stages of charging, developing just before the onset of conductivity. The results indicate that the hydroxide anion stabilizes the positive charges in PPy by NH bonding. The interaction is so strong that fixed bipolarons are formed without the intermediate formation of polarons. Polarons are produced only at higher charges with subsequent injection of mobile bipolarons and setting in of conductivity.