Solvation/desolvation during the redox transformation of poly(3-methylthiophene) (original) (raw)
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Electrochimica Acta, 2013
This work characterises the electropolymerisation of 3-methoxythiophene and presents an electrochemical study of poly(3-methoxythiophene) by cyclic voltammetry using different electrolytes in solvent mixture of water-acetonitrile (3:1, v/v) at 25 • C. Simultaneous measurements of the mirage effect and the quartz microbalance were also performed. This study evaluated the influence of cations on the electrochemical properties of monomers and polymers and allowed us to observe an anomalous behaviour of the synthesised polymer in the presence of potassium ions (K + ) when compared with other cations. The reversibility of the polymers was also evaluated with respect to the various electrolytes and was observed the influence of the polymer film thickness (deposited mass) on its electrochemical properties.
In situ spectroelectrochemical characterization of poly(3,4-ethylenedioxythiophene)
Electrochimica Acta, 1999
The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT), in dierent electrolyte±solvent media was studied with cyclic voltammetry, in situ UV±VIS-spectroelectrochemistry, electrochemical quartz crystal microbalance technique (EQCM) and with in situ Fourier transform infrared (FTIR) spectroscopy using external and internal re¯ection techniques. The eect of polymerization current density and monomer concentration on the formation of the ®lm structure was studied. The redox reactions and the stability of charged ®lms of dierent thickness were studied with cyclic voltammetry and open circuit potentiometric measurements. FTIR spectra were recorded in situ during step-wise and continuous potential cycling of the polymer ®lms in dierent electrolytes. A characterization of the doping induced IR-bands has been made. # Electrochimica Acta 44 (1999) 2739±2750 0013-4686/99/$ -see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 3 -4 6 8 6 ( 9 8 ) 0 0 4 0 5 -8 PERGAMON
Mixed ion transfer in redox processes of poly(3,4-ethylenedioxythiophene)
Journal of Electroanalytical Chemistry, 2004
A model considering the transfer of counter ions and solvent molecules has been presented to explain the complicated ion transfer in polymer films during electrochemical redox processes. The developed mixed ion transfer model is used to analyze the ion transfer behavior of poly(3,4-ethylenedioxythiophene) during doping and dedoping processes. The results indicate that both anions and cations are involved in n-doping as well as in p-doping processes. The behavior of different electrolyte ions is also studied. The developed model shows that solvent molecules are also transferred in conjunction with the ion transfer.
Polythiophene puzzle—a plausible solution
Journal of Electroanalytical Chemistry, 1998
Ž. Previous in situ spectroelectrochemical studies on the redox transformation of poly 3-methylthiophene have been completed by further electrochemical, EQCM and in situ conductance measurements. In the case of thicker films, the generally observed single, wide anodic voltammetric wave could be separated into two oxidation steps, which are not consecutive, but complementary processes. The mass vs. potential curve from the EQCM measurements also reflects the double pattern of the electronic process. The virtual stoichiometric factor per electron of the anion during the first oxidation is lower than 0.5, and it is close to 1 in the second oxidation region. The experimentally obtained smaller values are explained by the parallel removal of solvent. The conductance vs. logarithm of charge curves at small sweep rate show no hysteresis. However, during the first oxidation step the film is nonconducting; its transformation to conducting film is coupled with the second oxidation step. On the basis of the experimental observations, a detailed mechanism of the redox transformation is suggested in which the roles of the solvated and nonsolvated parts of the neutral film are distinguished. The achievement of the quasi-metallic state is connected to a capacitive process in which an intermediate of uncompensated charge is involved.
Redox switching mechanism of polythiophenes
Synthetic Metals, 1993
Spectroelectrechemieal studies of the anodic and cathodic redox processes of polymers of T-substituted 2,2':5',2"-terthiophenes provide information on the redox switching mechanism of polythiopbenes. A simple chemical model is to
Electrochimica Acta, 2006
The behaviour of poly(3,4-butylenedioxythiophene) (PBuDOT), a relative of poly(3,4-ethylenedioxythipohnene) PEDOT within the poly(3,4-alkylenedioxythiophene) family, has been investigated at potentials above its electrochemical stability threshold using in situ ESR spectroelectrochemistry. The aim was to investigate the effect of electrochemical overoxidation on the charge carrying species, namely polarons, normally generated and annihilated during reversible redox doping and dedoping reactions, by determining the potential dependencies of spectroscopic parameters of the ESR spectra of the polymer over a selected potential range. Specific features of the trends of these dependencies allowed also for an evaluation of presence of the second type of charge carrying species-diamagnetic bipolarons and the effects of their interactions with polarons at different potentials. Around 1.5 V, where the boundary of electrochemical stability of the polymer lies, sharp drop of the concentration of paramagnetic centres has been observed together with a transitory narrowing of the ESR line. These changes were found to be irreversible as evidenced by the course of subsequent reduction half-cycle, which differed from the one for a not overoxidised polymer, observed in previous studies. Aided by the results of electrochemical studies it was concluded that the overoxidation process leads to a degradation of the polymer most probably due decrease of the conjugation length of the main chain -bond through cross-linking or addition reactions. While the electrochemical results pointed to a non-complete degradation of the polymer, the specific parameters of the ESR line in the reduction half-cycle indicate that the remaining spins are confined to isolated segments of a partially degraded polymer where their behaviour resembles oligomer-like radicals. EA 11077 1-10 2 A. Zykwinska et al. / Electrochimica Acta xxx (2005) xxx-xxx space the polymer chains apart and by increasing the flex-53 ibility of the alkylene substituent, introduce some degree 54 of disorder in the relative arrangements of the polymer 55 chains, all of which could grant the respective polymer 56 solubility in common organic solvents. To date however 57 this approach alone proved unsuccessful in preparing a 58 soluble 3,4-alkylenedioxythiophene polymer. Nevertheless, 59 members of this polymer family displayed some interest-60 ing properties, sometimes markedly superior to their par-61 ent relative PEDOT. The spectroscopic studies indicated 62 that PProDOT displays a high degree of regularity along 63 the polymer backbone while PBuDOT displays one of the 64 fastest switching times together with one of the highest 65 optical contrasts ( %T amounting to 63%) in the poly(3,4-66 alkylenedioxythiophene) family [4]. Although the conductiv-N C O R R E C T E D P R O O F EA 11077 1-10 A. Zykwinska et al. / Electrochimica Acta xxx (2005) xxx-xxx 9 during electropolymerisation. Lorenz centres were attributed 481 to homogeneously distributed polaronic spins appearing on 482 the polymer's conjugated -bond upon doping, thus thought 483 to represent the electrons of conductivity in the polymer. This 484 assignment seems valid in this study as the concentration 485 of Lorenz type centres maps the overall concentration curve 486 while the Gauss type centres are practically potential insen-487 sitive. The fact that it is only the Lorenz type centres that 488 diminish during the sudden drop at 1.5 V further justifies their 489 assignment to polaronic spins. This decrease can be caused 490 by sudden oxidation to diamagnetic bipolarons as discussed 491 above or by recombination with free radicals that may be gen-492 erated upon overoxidation of the polymer, which seems more 493 probable in light of the irreversibility of this process. One pos-494 sible source of these free radicals may be the cleaved electron-1.5 V during oxidation. Changes in g-factor value indicate,
In situ studies of the transition from solution to solid film of poly(octylthiophene)
Synthetic Metals, 2001
The drying of thick solutions of the conjugated polymer poly(octylthiophene) (POT) was followed in situ by grazing incidence diffraction of synchrotron X-rays from the solution surface, with the solvent evaporation rate being controlled by a¯ow of dry nitrogen gas. It was found that a solid, partially crystalline ®lm is formed on the upper surface while the interior is still¯uid. The initially formed ®lm is swollen and of restricted correlation length, but the swelling disappears gradually on further drying. A considerable fraction (>20%) of the polymer within the effective beam volume near the surface is transformed from the disordered to the ordered state only during the removal of the last 5% of the solvent. #
Electrochimica Acta, 2014
Electrochemical polymerisation of 3-octylthiophene and 4,4 -dioctyl-2,2 -bithiophene in acetonitrile is reported. The nature of the resultant films was investigated through electrochemical and spectroelectrochemical means, in concert with quantum mechanical calculations to evidence the oligomeric nature of the deposits. Control of conjugation length through solubility modification is demonstrated through investigation of UV-vis spectra of polymers prepared in different solvents. ESR-UV-vis-NIR spectroelectrochemical measurements were used to gauge the differences in the behaviour of regioregular and regiorandom deposits. Conjugation length was found to vary significantly between the two polymers. This is shown to influence the nature of charge carriers generated upon p-doping of the system.
Electrochimica Acta, 1998
A new explanation of the asymmetry and large anodic residual current in the cyclic voltammograms for redox reactions of poly(3-methylthiophene) is proposed on the basis of voltammetric measurements for ®lms of dierent thicknesses. A specially designed measurement procedure shows that the anodic branch is a superposition of two overlapping oxidation peaks. The less positive peak is ascribed to oxidation of long-chain polymer segments which are formed mainly at the beginning of the electropolymerisation. The more positive peak originates from oxidation of short-chain segments which mainly contribute to the polymerisation of thick ®lms. Thick poly(3-MeT) ®lms, with polymerisation charges larger than 12 mC cm À 2 , are a mixture of the long-and short-chain segments due to participation of oligomers in the extended polymerisation process. The thin ®lms are better-ordered and more compact than the thicker ones. The change in morphology of the poly(3-MeT) ®lms is con®rmed by the scan rate dependence of currents of both anodic peaks and by the UV-VIS absorption spectra of the ®lms. #