Tosylate Ions Research Articles

White-green photoluminescence of manganese(II) complexes with pyrazolo[1,5-a][1,10]phenanthroline-3-carbonitrile

Five manganese(II) complexes with a bidentate pyrazolo[1,5-a][1,10]phenanthroline-3-carbonitrile ligand (L) have been prepared and their structures have been determined. The anion effect on the structural diversity of the complexes has been studied using manganese(II) salts with different anions such as Cl¯, ClO4¯, and Ts¯. A reaction between manganese(II) chloride and L in organic solvents leads to complexes [MnL2Cl2]·xCH2Cl2 (1) and [Mn2L2(H2O)Cl4]·L (2), the use of manganese(II) tosylate in the rection yields in [MnL(H2O)3Ts]Ts·L·H2O (3) and [MnL(H2O)3Ts]Ts (4), and finally, in the case of manganese(II) perchlorate [MnL2(H2O)2](ClO4)2·L (5) is formed. According to the single-crystal X-ray analysis the coordination environment of the Mn(II) ions in the complexes is a distorted octahedron with MnN4Cl2 (1), MnN2O4 (3) and MnN4O2 (5) chromophores; the complex 2 is binuclear, in which two manganese atoms have different coordination geometries – distorted octahedron (MnN2Cl3O) and square pyramid (MnN2Cl3). Chloride ions are coordinated anions; perchlorate ions are in the outer coordination sphere. Tosylate ions can play both coordinating and non-coordinating roles in complexes. X-ray analysis shows that in 2 and 5 one molecule of L has no bonds with manganese atoms, and reveals only intermolecular interactions through π-π stacking. This leads to the formation of cocrystals [Mn2L2(H2O)Cl4]·L or [MnL2(H2O)2](ClO4)2·L, that affects the photophysical properties of these compounds. In order to compare the effect of L coordination on the photoluminescence properties of manganese(II) complexes, the complexes [Mn(phen)3](ClO4)2·xSolv with unsubstituted 1,10-phenanthroline have been synthesized. In contrast to [MnL2(H2O)2](ClO4)2·L, the 1,10-phenanthroline-based compound [Mn(phen)3](ClO4)2·H2O has no emission. Complexes 1, 3, 4 and 5 exhibit a white-green emission in the microsecond range with maxima at 530–565 nm in the solid state, and the photoluminescence properties of 5 are studied in solution.

A negative piezo-conductive effect from doped semiconducting polymer thin films

In the past years, piezo-conductive sensors have drawn great attention in both academic and industrial sectors. The piezo-conductive sensors made by inorganic semiconductors exhibited poor mechanical flexibility, restricting their further practical applications. In this study, we report the piezo-conductive sensors by a semiconducting polymer, poly(3,4-ethylenedioxythiophene) doped with tosylate ions (PEDOT:Tos) thin films. Systemically studies indicate that the piezo-conductive response of the PEDOT:Tos thin films is originated from the deformation of the PEDOT crystal cells and the stretched π–π distances induced by Tos. Moreover, the negative piezo-conductive effect, for the first time, is observed from PEDOT:Tos thin film under the pressure. A working mechanism is further proposed to interpret the transient from a positive to a negative piezo-conductive response within the PEDOT:Tos thin films. Our studies offer a facile route to approach effective piezo-conductive sensors based on conjugated polymers.

Thermopower scaling in conducting polymers

By directly converting heat into electricity, thermoelectric effects provide a unique physical process from heat waste to energy harvesting. Requiring the highest possible power factor defined as α2σ, with the thermopower α and the electrical conductivity σ, such a technology necessitates the best knowledge of transport phenomena in order to be able to control and optimize both α and σ. While conducting polymers have already demonstrated their great potentiality with enhanced thermoelectric performance, the full understanding of the transport mechanisms in these compounds is still lacking. Here we show that the thermoelectric properties of one of the most promising conducting polymer, the poly(3,4-ethylenedioxythiophene) doped with tosylate ions (PEDOT-Tos), follows actually a very generic behavior with a scaling relation as α ∝ σ−1/4. Whereas conventional transport theories have failed to explain such an exponent, we demonstrate that it is in fact a characteristic of massless pseudo-relativistic quasiparticles, namely Dirac fermions, scattered by unscreened ionized impurities.

Large scale mobility calculations in PEDOT (Poly(3,4-ethylenedioxythiophene)): Backmapping the coarse-grained MARTINI morphology

Designing new high performances materials based on conducting polymers necessitates the development of multiscale models to investigate the charge transport in large realistic systems. In this work, we utilize Coarse-Grained (CG) Molecular Dynamics (MD) simulations to generate morphologies of Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with Tosylate (TOS) ions, and we develop a backmapping protocol to retrieve the atomistic details of the molecules afterwards. We demonstrate that the proposed protocol corrects for the nanostructure distortions induced by Coarse-Graining the system, namely a wrong density and an over-estimated π-π stacking distance. Quantum chemical calculations are performed on the systems obtained after backmapping in order to calculate hopping rates for charge transport, and charge mobilities as a function of the PEDOT chain length and hydration level are then calculated by solving a master equation for transport. The results are identical to the calculations performed on PEDOT morphologies obtained by direct All-Atomistic (AA) MD simulations: the mobility increases with the chain length and decreases with the hydration level, this last effect being more pronounced for short chains. This definitely shows that the workflow CG MD → backmapping → mobility calculations is in position to calculate charge mobility in PEDOT based materials, paving the way for theoretical investigations of transport in more complex materials such as PEDOT doped with Polystyrene Sulfonate (PSS).

A highly stretchable large strain sensor based on PEDOT–thermoplastic polyurethane hybrid prepared via in situ vapor phase polymerization

Strain sensors based on percolated networks of poly(3,4-ethylenedioxythiophene) (PEDOT) in thermoplastic polyurethane (TPU) matrix fabricated through in situ vapor phase polymerization (VPP) is reported. The hybrid made of elastomer and conductive polymer shows uniform PEDOT distribution on the surface and inner side of the TPU due to the effective penetration, diffusion, and polymerization of EDOT. Performance of sensors using two kinds of oxidants (FeCl3 or iron(III) p-toluenesulfonate(FTS)) are compared and the concentration is varied to obtain the best electromechanical properties. Amount of PEDOT increases with increasing amount of oxidant: thereby improving the electrical conductivity, while the elasticity of the hybrid decreases. The elasticity reduction phenomenon is diminished when FTS is used due to the plasticizer effect of the tosylate ion on the TPU. The performances of PEDOT–TPU hybrids prepared with FTS are excellent in the terms of stretchability (>300%), gauge factor (GF > 10 @ strain 100%), resistance variation reproducibility under various strain modes, small hysteresis, and durability (>1000 cycle). With the electromechanical performance, as well as cheap and scalable production, the PEDOT/TPU sensor holds tremendous prospects on flexible and stretchable devices for human motion monitoring, as well as present strategies on architecture of conductive soft materials.

(Invited) New Platforms for Multiplexing Electrochemical Measurements In Vivo

Complex behaviors depend on the coordination of the activities of ensembles of neurons and the release of neuromodulators such as dopamine. The mechanisms underlying such coordination are not well-understood due to a lack of instrumentation for combined and real-time monitoring of neuromodulator release and the activities of large ensembles of neurons. Here I describe a measurement platform that allows for the combined monitoring of electrophysiology from a high-density electrode array and dopamine dynamics from a carbon-fiber microelectrode. Integration of these two measurement systems was achieved through modification of the existing instrumentation. A shared grounded reference electrode was used in both systems to minimize electrical interference. Further, an optional solid-state-relay array positioned between the electrophysiological electrode array and amplifiers was added to provide additional electrical isolation. The capacity of the integrated measurement platform, termed DANA (Dopamine And Neural Activity), to measure action potentials (high frequency) and local-field oscillations (low frequency) was characterized in vitro using an artificial cerebral spinal fluid gelatin. In vivo recordings from the DANA platform in anesthetized rats demonstrated the ability of the system for near-simultaneous measurement of dopamine release and activity from multiple neurons both in distant brain regions (striatum and hippocampus) and within the same brain region (striatum). Furthermore, this system was shown to be sufficiently compact to measure activity in freely moving animals through recording of single-neuron activity, high-frequency local-field oscillations, and dopamine release. Fast scan cyclic voltammetry has been used extensively to monitor dynamic changes in neurotransmitters (e.g. dopamine, serotonin, norepinephrine) in real time. However, these measurements are limited in terms of the number of implantable sensors. This does not allow the coordinated chemical communication and interactions between groups of neurons to be mapped in the same animal. Additioanally, we present arrays of electrodes with biocompatible conducting polymers capable of measuring biogenic amines. Metal wires are coated with the electrochemical polymerization of the monomer 3,4-ethylenedioxythiophene (EDOT). After baking and rinsing, a film with a positively charged polymer backbone balanced by negatively charged tosylate ions is formed. These electrodes can then be easily integrated in mass-producible arrays, brining voltammetry on par with multiple probe recordings common in electrophysiology. These voltammetric recordings also require custom instrumentation that integrates low-noise operational amplifiers with high-performance data acquisition cards and software. The system presented is capable of recording from eight channels (with appropriate instrumentation). By electrically isolating each channel, they can be independently addressed and a different neurotransmitter can be measured at each sensor. This greatly increases the ability to map neurotransmitter release in the brain of animals in real time. Data measuring both dopamine and serotonin in different brain regions is presented.

A procedure for the preparation and isolation of nucleoside-5'-diphosphates.

Tris[bis(triphenylphosphoranylidene)ammonium] pyrophosphate (PPN pyrophosphate) was used in the SN2 displacements of the tosylate ion from 5’-tosylnucleosides to afford nucleoside-5’-diphosphates. Selective precipitation permitted the direct isolation of nucleoside-5’-diphosphates from crude reaction mixtures.

The odd association of a C3h trisamidinium cation and tosylate anion with a series of linear oxalate-bridged trinuclear heterometallic complexes

A series of six isostructural heterometallic trinuclear oxalate-bridged complexes of the formula (TDbenz)(2)(TsO)(2)[M(II)(H(2)O)(2){(μ-ox)M(III)(ox)(2)}(2)]·6H(2)O·2CH(3)OH (TDbenz = 1,3,5-tris[2-(1,3-diazolinium)]benzene; TsO = 4-methylbenzenesulfonate; ox = oxalate; M(III) = Fe, M(II) = Mn (1), Fe (2), Co (3); M(III) = Cr, M(II) = Mn (4), Fe (5), Co (6)) have been synthesized from (NH(4))(3)[M(III)(ox)(3)]·3H(2)O, the chloride salts of the divalent metal ions and the tosylate salt of 1,3,5-tris[2-(1,3-diazolinium)]benzene (trisamidinium). Whereas the crystal structures of compounds 2, 3, 4 and 5 have been investigated by single-crystal X-ray diffraction, the structures of 1 and 6 have been checked by X-ray powder diffraction. All six compounds are isostructural and crystallise in the P1 space group. The crystals are composed of discrete linear [M(II)(H(2)O)(2){(μ-ox)M(III)(ox)(2)}(2)](4-) trinuclear bimetallic units, trisamidinium and tosylate ions and solvent molecules. The linear trinuclear unit is based on a central trans-diaquametal(II) entity connected to two [M(III)(ox)(3)](3-) (M(III) = Cr(III), Fe(III)) moieties through oxalate bridges. The divalent metal ions, surrounded by six oxygen atoms, adopt a distorted octahedral coordination geometry. The coordination sphere is composed of four oxygen atoms belonging to two oxalate ligands and two trans-coordinated water molecules. One of the oxalate ions is coordinated to the central metal centre whereas the other two oxalate ligands are non-bridging. In the crystal, intermolecular hydrogen bonds involving oxalate ligands, solvent molecules and the counter-ions form a complex 3D network. Variable-temperature magnetic susceptibility measurements indicate an antiferromagnetic interaction between the iron(III) and the metal(II) ions (J = -4.23, -6.73, -8.97 cm(-1) for 1, 2 and 3 respectively) whereas this interaction is ferromagnetic when iron(III) is replaced by chromium(III) (J = +1.21, +2.20, +3.63 cm(-1) for 4, 5 and 6 respectively). Moreover, the cobalt(II) derivatives exhibit high D values (D = 29.3 cm(-1) for and D = 27.4 cm(-1) for 6).

Phosphonium-based ionic liquids in electrokinetic capillary chromatography for the separation of neutral analytes

In this work we elucidated the applicability of phosphonium-based ionic liquids (ILs) as pseudostationary phase in electrokinetic capillary chromatography (EKC) with UV-detection. The phosphonium ILs studied contain bromide, chlorine, or tosylate ions, as counter ions, and alkyl side chains of variable length on the phosphorous atom. The effects of the type and concentration of the IL, pH, ionic strength, and type of background electrolyte solution on the electroosmotic flow (EOF) and on the effective electrophoretic mobilities of some neutral model analytes were investigated and large variations in the migration times were observed. Especially the IL employed remarkably affected the strength and direction of the EOF Successful separations were obtained for neutral aromatic singly substituted analytes, namely benzene, toluene, phenol, and nitrobenzene. The results demonstrated the potential of capillary electromigration methods for rapid interaction studies between ILs and analytes, which is useful for the development of novel materials for sample preparation and separation purposes or for novel catalyst and chemical processing studies.

Aggregation and Adsorption at the Air–Solution Interface of the Cetyltrimethyl Ammonium Tosylate With Two Poly(oxyethylene)–Poly(oxypropylene)–Poly(oxyethylene) Block Copolymers Aqueous Mixtures

AbstractThe aqueous mixed systems (EO76PO30EO76) (TBCP8400)—cetyltrimethyl ammonium tosylate (CTAT), and (EO97PO69EO97) (TBCP12600)—CTAT were studied to determine both the bulk aggregation and the adsorbed monolayer at the air/water interface. Results were interpreted with the pseudophase separation model plus the regular solution theory for aggregates and monolayers. The behavior is different for TBCP8400–CTAT and TBCP12600–CTAT mixtures, but it is strongly non‐ideal in both cases. In bulk, TBCP8400–CTAT mixtures produce aggregates more close to CTAT micelles having TBCP8400 as a solubilizate than the inverse. At low CTAT content, the interaction is repulsive becoming attractive at high TBCP8400 content. The TBCP12600–CTAT aggregates strongly differ from the structure of both pure component micelles, and the interaction is always repulsive. In both cases, the interaction seems not to be cooperative but gradual. CTAT effect on copolymers aggregates seems to be more similar to that of a zwitterionic surfactant than to that of an ionic one. However, CTAT is not included in the aggregates as an ion pair, as revealed by the ionization degree results. It seems that cetyltrimethyl ammonium and tosylate ions have different effects on aggregates which in part are opposite. The adsorbed monolayers also show different behavior. In TBCP8400–CTAT system, the monolayer is mainly a CTAT one with inclusion of TBCP8400 as a monolayer‐soluble impurity. However, the inclusion of the non‐ionic surfactant alters the structure of the monolayer, which differs from that of the pure CTAT one. The area per adsorbed molecule (A0) is systematically higher than the ideal and computed ones. The system TBCP12600–CTAT shows a monolayer composition which is almost the same that the overall surfactant mixture composition, and the monolayer structure differs from both the pure‐TBCP12600 and the pure‐CTAT monolayers ones. The experimental A0 values are systematically lower than the ideal and the computed ones. Then, in both cases the A0 values for the pure components do not remain invariable in the mixed monolayer. The phenomenon is interpreted on the basis of the conformation of the copolymers adsorbed at the air/solution interface.

Electrochromic, magnetotransport and AC transport properties of vapor phase polymerized PEDOT (VPP PEDOT)

Poly(3,4-ethylenedioxy)thiophene (PEDOT) doped with tosylate ion (PEDOT–tosylate or VPP PEDOT) was synthesized by vapor phase polymerization (VPP) technique on glass as well as on glass/ITO and the electrochromic properties were investigated. Compared with that of PEDOT–PSS spin-coated on glass/ITO, the studies showed that VPP PEDOT has a lower work function and better electrochromic properties. The magneto and AC transport properties studies were done on VPP PEDOT coated on glass substrate. The system shows 2-dimensional variable range hopping and wave function shrinkage of charge carriers.

Thermal Decomposition of Triphenylphosphonium Alkyl Ester Salts

In thermolyses of molten triphenylphosphonium alkyl ester bromides and chlorides, alkyl = methyl, ethyl, isopropyl, at 130 and 225°C, initial attack of the halide ion on the methyl group gives the methyl halide and ylid 1 , Ph 3 P = CH 2 , which can be methylated, or is protonated by the phosphonium salt with transylidation giving Ph 3 P+-CH 3 X−, X = Br, Cl. The initial reactions of the ethyl or isopropyl esters are with the halide ion, X−, as a base giving ylid, 1 , which can be protonated by HX or by transylidation. The t-butyl ester generates Ph3P+-CH 3 X−but no products of transylidation. The first-formed ylid 1 , can be trapped by reactive alkyl and acyl halides, and the transient ylidic esters decompose thermally to triphenyl phosphine oxide, Ph 3 P = O, react further with unreacted phosphonium ester, or are trapped by added aldehyde in a Wittig reaction. The final product compositions are affected by a decrease in pressure, due to escape of volatile intermediates, and by replacement of the X− halide ion by the less nucleophilic and basic tosylate ion. Reactions under reflux, in solution in chloroform, or in suspension in benzene, are similar to those of the molten salts, but yields are generally lower at the lower temperatures.

Influence of components of the PdCl2(PPh3)2-PPh3-p-toluenesulfonic acid catalytic system on the rate of cyclohexene hydrocarbalkoxylation with m-cresol

Kinetic parameters were determined for the cyclohexene hydrocarbalkoxylation reaction catalyzed by the PdCl2(PPh3)2-PPh3-p-toluenesulfonic acid (TSA) catalyst system in the presence of m-cresol. It was shown that the reaction is first order in cyclohexene and a fractional order in PdCl2(PPh3)2 and m-cresol and that the dependences of the reaction rate on PCO, TSA and PPh3 concentrations are nonmonotonic in character. The inhibitory effect of tosylate and chloride ions on the reaction was revealed. The results were rationalized in terms of a mechanism that involves hydride complexes of the cation type as intermediates. A rate equation for the reaction was derived in terms of the steady-state hypothesis to fit to experimental data.

Shear moduli of anion and cation exchanging polypyrrole films

By using the acoustic impedance method, storage (G′) and loss moduli (G″) have been determined for poly(pyrrole) films grown on the gold electrode of an electrochemical quartz crystal microbalance from aqueous LiClO4 and sodium tosylate solutions. At 10 MHz, for 0.3–0.4 μm films G′ = 6 × 106, G″ = 2 × 106 dyn/cm2 for perchlorate and 2.5 × 108 and 1.1 × 108 dyn/cm2 for tosylate ions were determined. Cycling in the corresponding monomer free solutions did not significantly change the properties of the perchlorate anion film, but decreased the moduli of the tosylate films to 6–8 × 107 dyn/cm2. A slight increase of G during oxidation has been observed, i.e., the films are more stiff in the oxidized state.

Bio-characterisation of tosylate-doped polypyrrole films for biomedical applications

Electroactive polymers such as polypyrrole (PPy) are receiving particular interest because they can combine inherent biological properties that can specifically trigger desired cellular responses for many biological applications. The aim of the present work was to evaluate more efficient solutions, achieved by different oxidisations of tosylate-doped PPy films in different chemico-physical conditions, in view of their long-term biomedical applications. The conductivity and the release of the tosylate ion were assessed. Morpho-functional studies were also performed. A gradual increase in impedance of the oxidised tosylate-doped PPy films soaked in MEM and a reduced conductivity after over-oxidation was found. Scanning electron microscopy (SEM) analysis showed the presence of a hierarchical organisation of the PPy films and a partially different morphology between oxidised and over-oxidised films. Cell behaviour was also randomly affected in relation to the oxidative state of the studied Ppy films. On the basis of the results, growth of these tosylate-doped Ppy films directly in the sol–gel matrix or on the surface of metal alloys could be hypothesised in order to improve bioactive materials of potential use in modern regenerative medicine. However, in view of their in vivo application, over-oxidation must be considered as it may represent the degraded material that is likely to form under a biological oxidising environment.

Supramolecular interactions in metal tosylate complexes

Ammonium tosylate, hydrated metal tosylates ([Ca(H 2O) 4( p-SO 3C 6H 4CH 3) 2] and [M(H 2O)] 6( p-SO 3C 6H 4CH 3) 2 (M=Mg, Mn, Fe, Co, Ni and Zn) and [M(H 2O) 2(15-crown-5)]( p-SO 3C 6H 4CH 3) 2 (M=Mn, Co and Zn) have been crystallised from aqueous media and their structures determined by X-ray crystallography. The ammonium complex is an anhydrous species with a complex hydrogen bonding array. The structure of the calcium complex shows the tosylate is bound directly to the calcium centre through the SO 3 moiety, while the remaining isomorphous complexes all have a hexahydrated metal centre involved in a complex hydrogen bonded network through M–OH 2⋯O–S interactions. The crown ether containing compounds [M(H 2O) 2(15-crown-5)( p-SO 3C 6H 4CH 3) 2] (M=Mn, Co and Zn) have crown-encapsulated M(H 2O) 2 2+ ions with tosylate ions involved in hydrogen bonding bridging the cations in a one-dimensional polymer.

Monolayers of Hexadecyltrimethylammonium p-Tosylate at the Air−Water Interface. 2. Neutron Reflection

Neutron reflection has been used to determine the position of the p-tosylate ion in monolayers of the hexadecyltrimethylammonium cation (C16TA+) at the air−water interface. The monolayer was in equilibrium with a solution of composition 1 mM C16TAB and 3 mM sodium tosylate. The area per molecule of the surfactant was found to be 0.45 and 0.52 nm2 respectively in the absence and presence of tosylate and 0.42 nm2 in the presence of 3 mM NaBr. The ratio of tosylate to C16TA+ in the layer was found to be 0.8. Five isotopic species of the C16TA+ were labeled with deuterium in blocks of four atoms (C4D8, C4D9, or headgroup (CD3)3N), and the separation between the center of each of these blocks and the deuterated tosylate ion was determined. The values show that the average position of the tosylate ion in the layer is at exactly the same level as the third block of four carbons in the C16TA+ (the first block is defined as that containing the terminal methyl group); i.e., the tosylate ion is mainly in the hydroph...

Lyotropic Liquid Crystalline Main-Chain Viologen Polymers: Homopolymer of 4,4‘-Bipyridyl with the Ditosylate of trans-1,4-Cyclohexanedimethanol and Its Copolymers with the Ditosylate of 1,8-Octanediol

A series of viologen polymers based on 4,4'-bipyridyl and the ditosylates of trans-1,4-cyclohexanedimethanol and 1,8-octanediol was prepared by the quaternization reaction in acetonitrile. Their polyelectrolyte behavior in a common organic solvent was studied by viscosity measurements, and their chemical structures were determined by FTIR and 1D and 2D NMR spectroscopies. They were characterized for their lyotropic properties in a number of polar organic solvents by polarizing light microscopy and differential scanning calorimetry and for their photochromic properties by UV-vis spectroscopy. As expected, their inherent viscosity in methanol decreased dramatically with the increase in concentration in the absence of an added electrolyte. Although each of these polymers contained the ionic group along the backbone of the polymer chain, there was an array of weak ion-pair dipoles between the tosylate ion and the 4,4'-bipyridinium ion in each of them, which was indicated by the appearance of symmetric stretching band of S=O at a lower frequency (1034 cm -1 ) when compared with that of -SO 3 Na (1064 cm -1 ) in its IR spectrum. The aromatic protons of 4,4'-bipyridinium ion in each of these polymers exhibited three pairs of signals as opposed to a pair of doublets that generally occurs in small molecules containing this ion. These three pairs of signals were related to the structure and dynamics of these ionic polymers in a polar solvent such as methanol, which were studied by DEPT, 1 H- 1 H COSY, and NOESY spectroscopies. Each of them showed a lyotropic lamellar phase in methanol, ethanol, ethylene glycol, diethylene glycol, glycerine, and benzyl alcohol. Their critical concentrations (C * values) were as low as 5 wt % and as high as 20-40 wt %, and their concentrations for the development of fully grown lyotropic phase were as low as 10-20 wt % and as high as 40-50 wt % in various alcohols depending on the polarity of the solvents, the hydrophilicity and hydrophobicity of the solvents, and the microstructures of these polymers. Additionally, their lyotropic solutions in either glycerine or benzyl alcohol, on irradiation with UV light, produced a deep blue color in the presence of air, but in absence of both a photosensitizer and a sacrificial donor. This deep blue solution had two absorption bands at 390 and 608 nm, which are the characteristic absorption bands of the viologen cation radical. The generation of this blue color occurred due to the photoreduction of the 4,4'-bipyridinium moiety via the electron transfer from the tosylate counterion.

A spectroelectrochemical study on polaron transformations in polyaniline in sulphuric and p-toluenesulphonic acids

The electrochemical processes involved in the oxidation of polyaniline in sulphuric and p-toluenesulphonic acids were studied under steady potential and during a potentiostatic current transient using UV-Vis absorption spectroscopy. It was found that sulphate ions are reversibly inserted into the polymer film on oxidation and removed during reduction, while tosylate ions are irreversibly accumulated slowly in the film and protons are exchange instead. The redox peaks involve two independent transformation equilibria of three main species: reduced species, polaron and bipolaron of different chain lengths. While the charge involved in the polaron transformation is less than 20% of the charge involved safely in the oxidation of polyaniline before the onset of degradation, a significant capacitive contribution 40–60% was detected before the start of further oxidation of the polaron to bipolarons. Nernstian analysis of the redox process was possible only for the reverse scan and with the absorption peak of the reduced form. The spectroscopic transients showed that the oxidation, which is much slower than the reduction, is essentially the same in both acids without a significant contribution of the diffusion of dopant species in contrast with the reduction process. ©1997 SCI

A spectroelectrochemical study on polaron transformations in polyaniline in sulphuric andp-toluenesulphonic acids

The electrochemical processes involved in the oxidation of polyaniline in sulphuric and p-toluenesulphonic acids were studied under steady potential and during a potentiostatic current transient using UV-Vis absorption spectroscopy. It was found that sulphate ions are reversibly inserted into the polymer film on oxidation and removed during reduction, while tosylate ions are irreversibly accumulated slowly in the film and protons are exchange instead. The redox peaks involve two independent transformation equilibria of three main species: reduced species, polaron and bipolaron of different chain lengths. While the charge involved in the polaron transformation is less than 20% of the charge involved safely in the oxidation of polyaniline before the onset of degradation, a significant capacitive contribution 40-60% was detected before the start of further oxidation of the polaron to bipolarons. Nernstian analysis of the redox process was possible only for the reverse scan and with the absorption peak of the reduced form. The spectroscopic transients showed that the oxidation, which is much slower than the reduction, is essentially the same in both acids without a significant contribution of the diffusion of dopant species in contrast with the reduction process.