Potential-Driven Conductivity of Polypyrroles, Poly- N -Alkylpyrroles, and Polythiophenes: Role of the Pyrrole NH Moiety in the Doping-Charge Dependence of Conductivity (original) (raw)
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Electronic Conduction in Polymers. I. The Chemical Structure of Polypyrrole
Australian Journal of Chemistry, 1963
The pyrolysis of tetraiodopyrrole in an inert atmosphere at temperatures from 120-700� yields black, infusible, amorphous polymers insoluble in solvents. Depending on the pyrolysis temperature, iodine may be present in the polymers as iodine of substitution and as chemisorbed molecular iodine, which is very tenaciously held. As a first approximation, the structure may be regarded as a three-dimensional network of pyrrole rings cross-linked in a nonplanar fashion by direct carbon to carbon linkages. The secondary nitrogen atoms form a hydroquine type system which may be oxidized by iodine or molecular oxygen under alkaline conditions. The extent of oxidation depends on the hydroxyl ion concentration. The nonplanarity of the oxidized quinonoid system renders it unstable but stability is enhanced, as in the triphenylmethane dyestuffs, by the formation of a carbinol. Despite their nonplanarity polypyrroles are relatively good conductors of electricity. The resistivity ranges from 1-200 ...
Journal of the American Chemical Society, 1990
In situ measurements of the relative conductivity of polythiophenes, polyaniline, and polypyrroles as a function of clectrochemical potential reveal that they have finite potential dependent windows of high conductivity. Further, the high conductivity is found where charge is injected or withdrawn from the polymer. The polymers studied, polyaniline and I-VI, are prepared by anodic polymerization onto microelectrode arrays of the appropriate monomer: thiophene (I), 3-methylthiophene (11). 3-phenylthiophene (Ill), 1-methyl-I'-(3-(thiophene-3-yl)propyl)-4,4'-bipyridinium (IV), 3,4-dimethylpyrrole (V), and N-methylpyrrole (VI). The use of a liquid SO,/electrolyte medium as the electrochemical solvent makes it possible to define the window of high conductivity, because it allows the polymers to be reversibly oxidized to a greater extent than has previously bccn achicved. The conductivities of I-IV increase by at least 106-109 when they are oxidized from neutral to the potential of maximum conductivity and then decrease by 10'-10' when they are further oxidized to the greatest extent possible without irrcvcrsible degradation in liquid S02/electrolyte. Cyclic voltammetry indicates that IV is oxidized by-0.3 electron per thiophene repcat unit at the potential of maximum conductivity and by-0.5 electron per repeat unit at the most positive potential accessible without irreversible degradation. Visible-near-infrared absorption spectroscopy of I1 at the most positive potential accessible is similar to that at the potential of maximum conductivity, the spectrum having a broad peak extending into the infrared. For thiophene-based polymers I, 11, 111, and IV, the maximum conductivities are approximately IO-', 10, 5 X and 5 X IO-' Q-' cm-I, respectively, and the widths of the windows of high conductivity are 0.77, 0.98,0.65, and 0.47 V, respectively. Thc trend for both properties is I1 > 1 > 111 > IV, consistent with theoretical considerations relating conductivity, band width, and carrier delocalization. Polyaniline undergoes large, reversible, potential dependent changes in conductivity in liquid S02/electrolyte in the apparent absence of a protonation/deprotonation mechanism. Conductivity increases by at least IO8 upon oxidizing polyaniline from neutral to maximally conducting and decreases by at least IO8 when polyaniline is further oxidized in the cyclic voltammogram. Polyaniline can be taken to-+3.8 V vs SCE in liquid SO,/electrolyte without irreversible degradation. Visible-near-infrared spectroscopy shows that fully oxidized polyaniline absorbs only at high energy with no absorption at the low energy end of the near infrared. Potential dependent windows of high conductivity and cyclic voltammetry for pyrrole-based polymers V and VI are similar to those for thiophene-based polymers I-IV.
Pure and Applied Chemistry, 1997
The present paper describes some recent results concerning processable electroconducting materials prepared starting with properly substituted pyrrole derivatives. The first approach was based on the preparation of a precursor polymer by free radical polymerization of N-vinylpyrrole. This insulating, soluble and filmable polymer could be converted into an electroconducting product by intramolecular ladderization through oxidation of the pyrrole side chains. In the same frame the chemical homo and copolymerization of 3-decylpyrrole with pyrrole allowed to produce soluble or swellable polymers having conductivity variable with copolymer composition. The ladder formation and internal plastification by the long aliphatic side chain have been combined to give polymers derived from 3-decyl-N-vinylpyrrole and its copolymers with N-vinylpyrrole. Relationships between electroconductivity and controlled structure of the subject materials are discussed with reference to their blends with insulating plastomers.
dc Conduction in electrochemically synthesized polypyrrole films
1998
DC conductivity measurements were performed by modified four-probe rig on electrochemically synthesized polypyrrole films at a temperature range of -30 • C to 120 • C. Conductivity increased with temperature. The temperature dependence of conductivity was very high for lightly doped polymers, decreasing as the doping level increased. The model used to describe the conduction process was the conduction model originally developed for amorphous silicon by Mott and Davis. When applied to conducting polymers, it assumes that electron transport originates from localized or fixed states within the polymer chain. The charge transfer between the chains takes place by hopping, referred to as phonon-assisted hopping, between two localized states. Plots of DC conductivity versus temperature can be parametrized by Mott's Variable Range Hopping conduction model. The DC conductivity of polypyrrole films doped from light to intermediate levels with p-toluene sulphonic acid were measured in the temperature range of 77K to 300K. The localization length of localized electrons was assumed to be 3Å, which is approximately equal to the length of the pyrrole monomer. Mott parameters of polypyrrole films doped with p-TS were evaluated at 300K and 10K. Results were found to be consistent with the Mott's requirement that αR >> 1 . Theoretical values of α and N (EF ) have been determined at approximately 10 8 cm −1 and 10 19 -10 20 cm −3 eV −1 , respectively. Hence according to Mott parameters determined by the experimental data for the p-TS doped polypyrrole samples, Mott parameters are seen to have a better agreement with those expected from disordered systems, particularly for lightly doped samples, indicating the suitability of Mott's model to these samples. The average hopping distance R decreased from 16Åto 4.4Åwith the increase in the doping level from 0.006 M to 0.03 M at 300K, whereas at 10K, R decreased from 37Å to 10Å over the same dopant range.
Halomethylpyrroles as candidate monomers for conducting polymers: a theoretical study
Chemical Physics, 2004
Structural, electronic, thermochemical and electrical properties of mono-, di-and trihalomethylpyrroles (HMPys), NC 4 H 4-CH n X 3 À n ; X = F, Cl, Br; n = 0, 1, 2, 3, and their radical cations have been studied using DFT-B3LYP method with 6-31G(d,p) basis set. Vibrational frequencies and NMR shielding constants of these compounds have also been calculated and analyzed. HMPys are proposed in this research as candidate monomers for conducting polymers with modified characteristics compared to polypyrrole and polymethylpyrrole. Stability of HMPy radical cations have been studied in detail and compared with available experimental data, including oxidation potentials. Results of the present study show that bromomethylpyrroles have the highest thermochemical stability and have higher characteristics for electropolymerization compared to fluoro-and chloromethylpyrroles. Stability of HMPys increases with increasing number of substituted halogen atoms.
Electrical Properties of Polypyrrole Conducting Polymer at Various Dopant Concentrations
Polypyrrole conducting polymer was prepared by chemical reaction method with various concentrations of iron (III) chloride (FeCl3) as dopant. The dc conductivity was obtained from current-voltage characteristic by using parallel-plate techniques in the temperature range of 100-300K. With the involvement of chloride, Cl -in the polymeric chain, the conductivity increased as temperature and the dopant concentration increased. To describe the electrical transport process, Mott's 1-D, 2-D and 3-D variable range hopping (VRH) models have been considered. The result gives evidence of transport mechanism based on Mott's 3-D VRH mechanism for all various dopant concentrations studied.
International Journal of Electrochemical Science
Conducting homo-, bilayered-and co-polymers of 3-methylthiophene (MT) and N-methylpyrrole (NMPy) were electrochemically deposited on platinum electrode. Electrochemical investigation of the resulting films was achieved using cyclic voltammetry and chronocoulometry. The diffusion coefficients were calculated in case of using different films of different thicknesses. The synthesis and testing the films in presence of different types of electrolytes and solvents were studied. The results showed that a memory effect caused by the synthesis anion affects further interaction between the film and the test anion which consequently affect the diffusion coefficient. The charge spacing effect caused by the type of electrolyte is more pronounced in the case of PMPy compared to PMT. Also, diffusion coefficient values were calculated for films with different thickness prepared from different monomers feed ratios in different electrolytes and solvents. Some of them showed similar trend to the homo-polymers. For conducting bilayers, the inner layer influences the redox process of the bilayer. This can be showed from the cyclic voltammetry measurements and diffusion coefficient calculations. FTIR measurements proved the incorporation of both individual monomers in the copolymer films. TGA proved that the thermal stability of the copolymer increased by increasing NMPy content. On the other hand, surface morphology revealed by SEM showed a distinct difference between homo-and copolymeric structures.
On the structure and transport properties of polypyrroles
1992
Conducting organic polymers have attracted much attention as electronic materials, since Shirakawa et al. reported [1] an increase of several orders of magnitude in the electrical conductivity of polyacetylene after reaction with oxidants. This oxidative process giving positively charged structures is known as ,,doping,, owing to its analogy with the doping process for inorganic semiconductors. However, from a chemical point of view, the two types of doping correspond to different types of chemical transformation [2]: the oxidative process upon the non-conducting neutral polymer results in an positively charged oxidized molecule which in its solid structure requires the incorporation of a counter anion. Obviously, the nature of this anion determines the physical properties of the material. In spite of the high electrical conductivities reported for polyacetylene [3] (see Scheme 1) it rapidly degenerates in air. Other it conjugated organic conductors are thus attracting more attentio...
Journal of Solid State Electrochemistry, 2007
Conducting polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl-β-cyclodextrin) [poly(Py-β-DMCD)] films were prepared by electrode potential cycling on a gold electrode in aqueous and nonaqueous (acetonitrile) electrolyte solutions containing lithium perchlorate. The resulting products were characterized with cyclic voltammetry, in situ UV-Vis spectroscopy, and in situ conductivity measurements. For the electrosynthesis of poly(Py-β-DMCD), a (1:1) (mole-mole) (Py-β-DMCD) supramolecular cyclodextrin complex of pyrrole previously characterized with proton NMR spectroscopy was used as starting material. A different cyclic voltammetric behavior was observed for pyrrole and the poly(Py-β-DMCD) complex in aqueous and nonaqueous solutions during electrosynthesis. The results show that in both solutions in the presence of cyclodextrin, the oxidation potential of pyrrole monomers increases. However, the difference of oxidation potentials for films prepared in aqueous solution is larger than for the films prepared in nonaqueous solution. In situ conductivity measurements of the films show that films prepared in acetonitrile solution are more conductive than those synthesized in aqueous solutions. Maximum conductivity can be observed for PPy and poly(Py-β-DMCD) films prepared in nonaqueous solution in the range of 0.10<E Ag/AgCl < 0.90 V and 0.30<E Ag/AgCl <0.90 V, respectively. In situ UV-Vis spectroelectrochemical data for both films prepared potentiodynamically by cycling the potentials from −0.40 < E Ag/AgCl < 0.90 V in nonaqueous solutions are reported.