V. E. Kazarinov

Electrochemical and photoelectrochemical behaviour of polythiophenes in non-aqueous solutions - Part 2. The effect of charge trapping

Abstract The irreversibility of the doping–undoping processes and its effect on the electrochemical and photoelectrochemical behaviour of conducting polymers was studied for a series of polythiophene derivatives: polybithiophene, poly-3-methylthiophene and poly-3-phenylthiophene. For the three polymers it was confirmed that both anodic and cathodic undoping processes involve a considerable amount of residual charge trapped in the polymer phase. The nature of charge trapping for all the polymers was related to the incompleteness of the undoping processes rather than the chemical modification of the polymer, although the latter was also shown to occur. It was demonstrated that the trapped charge can be removed not only electrochemically (at the beginning of the polymer doping process of the opposite sign), as has been shown earlier, but also photoelectrochemically, by illuminating the polymer in solution at appropriate electrode potentials where the cathodic photocurrents are observed. The latter fact suggests that the photoelectrochemical undoping of these polymers observed by us earlier is in fact related to the photoassisted removal of the trapped charge.

Electrochemical and photoelectrochemical behaviour of poly-3-methylthiophene and polybithiophene in non-aqueous solutions: 1. Dark and light processes in systems with and without cathodic doping

The electrochemical as well as the photoelectrochemical behaviour of poly-3-methylthiophene and polybithiophene in systems with and without the possibility of cathodic doping was studied. Using electrochemical impedance measurements it was demonstrated that in both types of systems the photoelectrochemical processes on such polymers involved photoelectrochemical undoping of the polymer itself as well as the photoelectrochemical reduction of a component of an external redox couple in the solution. In systems with cathodic doping, in addition to these two processes, photoassisted cathodic doping of the polymer is observed. The model of photoelectrochemical processes on polymer electrodes is discussed.

Two types of retarded charge in the electron-conducting thiophene polymers

A study of the cathodic and anodic doping of polybithiophene and poly-3-phenylthiophene in acetonitrile and propylene carbonate demonstrates that the main fractions of charges of either sign undergo quasireversible redox conversions. Two types of retarded processes reveal themselves. One is associated with conversions of residual portions of positive and negative doping charges trapped in the nonconducting matrix of a neutral polymer at final stages of the undoping process. The other is due to redox conversions of polymer chemically modified when interacting with solution components.

Solvent effects in the electric double-layer structure for gallium and gallium-like metals

Abstract Effects of a specific interaction between the solvent and the metal in the electric double layer structure in a surface-inactive electrolyte solution are considered, based on experimental data for the gallium group of metals in various solvents: water, acetonitrile, dimethylsulphoxide, dimethylformamide and N-methylformamide. A donor-acceptor interaction between the metal and chemisorbed solvent molecules is shown to exist, the solvent being an electron donor with respect to the metal. The problem of orientation of chemisorbed solvent molecules at a uncharged metal surface is analysed.

Electrochemical reduction of 2,6-diphenylpyrylium cations by spin-polarized electrons on p-GaAs photocathodes

Abstract The electrochemical reduction of 2,6-diphenylpyrylium cations on p-GaAs photocathodes was carried out under conditions of optical orientation of electron spins in the semiconductor. Optical orientation caused spin-polarization of the pyranyl radicals formed on p-GaAs and thereby hindered the rate of the following stage of radical dimerization, decreasing the rate of the overall process. The reliability of the effect of spin-polarization was proved by comparison with reduction processes in systems where spin-polarization of radicals does not occur or does not affect the rate of the reduction process.

Effect of light on the poly-3-phenylthiophene properties

The electrochemical and photoelectrochemical behavior of a conducting polymer, poly-3-phenylthiophene (P3PhT), is studied in acetonitrile containing salts of tetrabutylammonium (TBA) and lithium. Like other thiophene polymers, P3PhT may or may not be doped cathodically in the presence of salts of TBA or lithium, respectively. In general, the photoelectrochemical behavior of P3PhT resembles that of polybithiophene and poly-3-methylthiophehe. In particular, P3PhT is photoactivated when exposed to light at negative potentials. Depending on the system in which measurements are taken (in the presence of salts of lithium or TBA), P3PhT undergoes photoelectrochemical undoping or photoelectrochemical cathodic doping, respectively, which is confirmed by measuring electrochemical impedance. However, the photoelectrochemical processes on P3PhT (at least in solutions containing lithium salts) proceed much slower than those on other thiophene polymers we studied earlier. The concentration of doping ions in P3PhT in the presence of lithium salts is higher than that in the presence of TBA salts even in the undoped state. This is due to a specific interaction between Li+ and the phenyl group in P3PhT.

Effect of solvent and supporting electrolyte on redox conversions of electropolymerized copper tetraaminophthalocyanine

Electropolymerization of copper tetraaminophthalocyanine in dimethyl sulfoxide (DMSO) is studied, along with redox conversions of this polymer inDMSO and propylene carbonate (PC). At cathodic potentials, redox conversions of the polymer are similar to those of the monomer. At anodic potentials, the polymer exhibits some redox activity in PC and almost none, inDMSO. The redox conversions are attributed to the formation of a common system of conjugated bonds.

Electrochemical methods for analysis of the thickness of thin alternating metal layers

Abstract A number of methods are proposed for determining the thickness of alternating metal layers with different electrochemical activities in the same electrolyte. The selection of a particular method is determined by anodic behavior of the metal. An appropriate choice of the electrolyte and the dissolution regime for every layer (including a combination of the proposed methods) allows us to simplify markedly the procedure of determining the multilayer deposit thickness, to enhance the measurement accuracy and to extend the range of measurable deposits.