Conformation and electronic structure of poly(3,4-diisopropylidenecyclobutene), a cross-conjugated conductive polymer

It has been reported recently that the title polymer, 1, synthesized by a novel olefin-metathesis route, can be oxidatively doped to yield materials with moderate conductivities. Theoretical studies reveal that, due to steric crowding, polymer 1 cannot achieve a planar, fully-conjugated structure in either its undoped or doped states. Rather, the structure consists of essentially orthogonal tetramethylhexatriene units. Such a structure is incompatible with conventional conduction mechanisms involving polarons or bipolarons. It is proposed that, instead, conduction involves intra- and/or inter-chain charge transfer.     

Ex situ XANES,XPS and Raman studies of poly(3,4-ethylenedioxythiophene) modified by iron hexacyanoferrate

X-ray (XPS and XANES) and Raman spectra of poly(3,4-ethylenedioxythiophene) (pEDOT) modified by iron hexacyanoferrate (Fehcf) network are presented. XANES studies allowed to postulate an octahedral surrounding of iron atoms in the material and identified nitrogen and carbon atoms as nearest neighbourhoods. XPS measurements reveal iron–nitrogen and iron–carbon bonds, supporting the XANES results. Chemical interaction between sulphur from pEDOT and iron was also evidenced by XPS. Although both methods give proof of Prussian Blue structure inside the polymer, Raman studies did not show any signal typical for CN at about 2160 cm^?1 (ν). However, the presence of Fehcf was confirmed by the stretching vibrations of Fe–N bond at 146 cm^?1 and Fe–CN vibrations at 270 cm^?1. AFM imaging was performed to illustrate the roughness and morphology of the pEDOT/Fehcf surface.     

Long alkyl chain bearing derivatives of poly(3,4-ethylenedioxythiophene) studied by in situ EPR spectroelectrochemistry

Electrochemically synthesised polymers of long, 2-oxaalkyl chain derivatives of 3,4-ethylenedioxythiophene (EDOT) have been studied using in situ EPR spectroelectrochemistry. Originally developed as promising candidates for preparation of soluble PEDOT derivatives, their polymers themselves reveal interesting spectroelectrochemical properties, in some cases even superior to their family's parent. Our results indicate notable differences in potential dependencies of concentration of spins and ΔB_pp width between the two polymers, indicating a major influence of the alkyl side chain length on specific properties of paramagnetic charge carriers appearing in these polymers in the course of their redox processes. Certain features of their spectroscopic response however, like the hysteresis of potential dependence of concentration of spins and ΔB_pp widths, point to similarities of their doping - dedoping mechanism with the one of PEDOT.     

Amperometric alcohol biosensors based on conducting polymers: Polypyrrole,poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxypyrrole)

Alcohol biosensors based on conducting polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxypyrrole) (PEDOP) were constructed. Alcohol oxidase (AlcOx, from Pichia pastoris) was immobilized during electropolymerization of the monomers in sodium dodecylsulfate (SDS) and phosphate buffer electrolysis medium. Optimization of several parameters was carried out. The highest affinity was observed for the PEDOT/AlcOx sensor. Lowry protein determination method was also used to calculate the amount of immobilized enzyme in sensors. Before testing the biosensors on alcoholic beverages effects of interferents (glucose, acetic acid, citric acid, and l-ascorbic acid) were determined. The alcohol contents of the distilled beverages (vodka, dry cin, whisky, and rak?) were determined with the sensors constructed. A good match with the chromatography results was observed.     

Conductivity of de-doped poly(3,4-ethylenedioxythiophene)

The conductivity of chemically and electrochemically de-doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been investigated in situ. We observe a decrease in the conductivity by 4–5 orders of magnitude. The change of conductivity is correlated to the change of electronic structure. We obtain the dielectric function of the polymer by spectroscopic ellipsometry and note that anisotropy is observed in both doped and neutral states.     

Electro-conductive properties of poly(3,4-ethylenedioxythiophene)/poly(ionic liquid) films with respect to its structure and morphology

Poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(1-vinyl-3-ethylimidazolium⁺ (trifluoromethane sulfonyl)imide^?) (PIL) complexes were prepared at various PEDOT/PIL molar ratios and dispersed in propylene carbonate at a concentration of 1 wt%. After casting, the maximum conductivity was measured to be 1.2 × 10^?1 S/cm, which could be explained by the 3D variable range hopping model. The optimum surface roughness of the PEDOT/PIL film was measured, showing S_a and S_q values of 5.92 and 11.0 nm, respectively. The conductivity of the polymerized PEDOT without a template process had low conductivity due to its poor surface roughness and large particle size. Therefore, the conductivity of PEDOT/PILs is determined by the particle size, crystallinity and surface morphology. These results were supported by surface mapping microscopy, X-ray photon spectroscopy, and X-ray diffraction.     

Reflectance of conducting poly(3,4-ethylenedioxythiophene)

We present the reflectance spectrum of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with PF₆ with dc conductivity of 230 S/cm at room temperature, measured over a wide frequency range from 50 to 5×10⁴ cm⁻¹ (0.006–6 eV). The reflectance, R(ω), of PEDOT-PF₆ is characterized by metal-like signatures in the infrared (IR), including high R(ω) in the far-IR and a plasma frequency of approximately 1.2 eV. The optical conductivity, σ(ω), is dominated by intraband contributions below 1 eV, characteristic of a disordered metal near the metal–insulator (M–I) transition. The reflectance spectrum is in good quantitative agreement with the “localization-modified Drude (LMD) model”. Since the onset of the interband absorption (below 1.5 eV) is at lower energy than in other conducting polymers, PEDOT-PF₆ shows low absorption in the visible range between 2 and 3 eV. Our spectroscopic results demonstrate that this doped PEDOT system can be utilized as a transparent electrode for optoelectronic devices.     

Modification of poly(3-methylthiophene) (PMeT) structure during electrochemical doping-undoping,studied by in situ atomic force microscopy (ECAFM)

Doping and undoping of poly(3-methylthiophene) (PMeT) layers were performed in an electrochemical atomic force microscopy (ECAFM) microcell, and images accounting for modification of the polymer surface were continuously recorded. The main result is that the variation of polymer morphology is very slow in relation to the modification of doping charge. The discrepancy between the two time constants, related respectively with ion and solvent molecule transfer and by electronic charge transfer, was emphasized by in situ ellipsometry. In this case the variation of optical properties against doping charge is very fast.     

Vacuum ultraviolet spectroscopy of the optical properties and electronic structure of seven poly(di-alkylsilanes)

We report the ultraviolet (UV) and vacuum ultraviolet (VUV) optical properties and electronic structure, up to 44 eV, of thin-film samples of seven poly(di-alkylsilanes) [alkyl = n-butyl, n-pentyl, i-hexyl, n-hexyl, n-octyl, and n-tetradecyl] with three types of Si---Si backbone conformations: helical, planar zigzag, and trans-gauche-trans-gauche' (TGTG′). The backbone conformation determines the UV transitions, with helical materials exhibiting one near-UV absorption, while two UV transitions are seen for the two-phase materials containing both the helical and planar zigzag backbone conformations. The TGTG′ backbone exhibits a single UV absorption at 3.6 eV. At higher energies all materials show a prominent shoulder at 7.2 eV, with a doublet peak structure seen at ≈ 9 and ≈ 12 eV. The 7.2 eV transition is unaffected by the backbone conformation or alkyl substitution, while comparison with the electronic transitions in polyethylene shows that the high-energy double-peak structure corresponds to transitions in the hydrocarbon sidechains. The ≈ 12 eV transitions appear to shift to higher energy with increasing sidechain length and in tetradecyl these sidechain transitions are noticeably narrowed, suggesting unusual sidechain crystallization in poly(di-n-tetradecylsilane). A hierarchy of electronic transitions can be developed whereby the UV transitions arise in the Si backbone, at intermediate energies backbone to sidechain transitions are observed, while the high-energy transitions are of the alkyl sidechains. This hierarchy in the electronic transitions demonstrates the ability of VUV spectroscopy of the electronic structure to serve as a microscopic probe of the bonding and structure of polysilanes, for example providing detailed insight into the properties of the sidechains in these polymers.     

Copper modified poly(3,4-ethylenedioxythiophene): Part II: Potentiostatic experiments

The electrochemical reduction of copper ions is investigated at poly(3,4-ethylenedioxythiophene) (PEDT) coated electrodes by means of potentiostatic experiments, cyclic voltammetry and ESR measurements. It is established that copper deposition at low overpotentials allows stabilization of a considerable amount (up to 10%) of copper species in the polymer layer and impeding the copper crystallization process. An additional redox couple is found to appear at the PEDT voltammogram showing two different valence states of the copper/polymer related species. ESR and electrochemical measurements allow concluding that the redox couple is related to the formation of a [Cu(I)PEDT]⁺ complex and corresponds to the [Cu(I)PEDT]⁺+e⁻↔Cu(0)PEDT reaction. ESR spectra show that Cu atoms specifically bonded to the polymer disturb the PEDT paramagnetic system.     

Synthesis of highly conductive poly(3,4-ethylenedioxythiophene) fiber by simple chemical polymerization

Poly(3,4-ethylenedioxythiophene) (PEDOT) fiber was chemically synthesized by the polymerization of 2,5-dihalo-3,4-ethylenedioxythiophene in the presence of BF₃ without a template. The resulting conductive PEDOT fiber exhibited conductivity in the range of 150–250 S/cm (pressed powder pellet). The thermal stability of PEDOT was also improved and UV-spectroscopy analysis of a film exhibited a strong absorption band at 460 nm. The well-defined needle-shaped fibers of PEDOT were examined by SEM, and the average length and diameter of the fibers were 10 and 0.4 μm, respectively.     

One-step fabrication of conductive poly(3,4-ethylenedioxythiophene) hollow spheres in the presence of poly(vinylpyrrolidone)

Poly(3,4-ethylenedioxythiophene) (PEDOT) hollow spheres with the size ranged from 130 to 820 nm and a conductivity of 8 × 10^?2 S cm^?1 were prepared simply and directly via a one-step self-assembly approach in the presence of poly(vinylpyrrolidone) (PVP) as a soft template. It was found that the formation probability of PEDOT hollow spheres depended on the concentration of PVP. Bulk quantities of PEDOT hollow spheres can be obtained readily under the optimal conditions such as the concentration of PVP > 0.175 mM and PVP/EDOT molar ratio <1.4. The electron-rich oxygen atoms on the lactam groups in PVP were proposed to act as the chemically active sites to anchor EDOT cation radicals by virtue of electrostatic interaction and cause the self-assembly of PEDOT hollow spheres. Our investigation for the formation mechanism of PEDOT hollow spheres may shed some light on preparing of other hollow materials by proper molecular design and experimental condition optimization.     

Spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) in aqueous medium

The in situ electrochemical doping process of the poly(3,4-ethylenedioxythiophene) (PEDT) has been studied in an aqueous micellar medium by means of optical spectroscopies. The cyclic voltammetry (CV) and optical absorption results were compared with previous ones obtained either in acetonitrile or in water without surfactant. No significant effect of the medium, water or acetonitrile, was found, but the presence or absence of surfactant in water give rise to different doping CVs, especially in the reductive part. Resonant Raman scattering experiments show a behavior of PEDT different from the one in acetonitrile. The doping mechanism we deduced from these results should imply a variation between an “intermediate” electronic conformation of the polymer in the reduced state to a predominant benzenic one during doping. The comparison with our previous results obtained in acetonitrile leads us to think that the reduced PEDT is in fact slightly oxidized by the aqueous medium.     

Electro-assisted precipitation of electrolytes in poly(3,4-ethylenedioxythiophene) film

The electrolyte, NaBF₄, can be enriched into the matrix of poly(3,4-ethylenedioxythiophene) (PEDOT) film during the p-doping potential cycling between 0.6 and −0.9 V. It has been demonstrated that this enrichment is originated from the mixed ion transfer between doping and dedoping, i.e. BF₄⁻ anion migrate into the PEDOT film during the oxidation process, the Na⁺ cation insert into the film during the reduction process, and then, the electrolyte is accumulated into the film matrix after the multiple CV cycling. The quantitative analysis of energy-dispersive X-ray spectroscopy (EDX) confirmed the enrichment of NaBF₄ in the PEDOT film.     

Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) films with improved thermoelectric performances

Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films with room-temperature electrical conductivity of about 300 S cm^?1 were successfully prepared from PEDOT/PSS solution containing additives (DMSO or EG) on the smooth and flexible polypropylene (PP) film substrate with contact angle of 87°. As formed free-standing PEDOT/PSS films possess good flexibility and can be easily cut into various shapes with a knife. The contact angle of substrate has significant effect on the preparation of free-standing PEDOT/PSS films. Additionally, the process of adding DMSO or EG did not result in the change of carrier concentration but the increase of carrier mobility. The free-standing PEDOT/PSS film showed high electrical conductivity and stable Seebeck coefficient and its figure of merit (ZT) with high environment stability can be up to 10^?2, one order of magnitude higher than that of pressed PEDOT/PSS pellets (10^?3).     

XPS and IR study of electrochemically or chemically redoped poly(3-methylthienylene) films

XPS (X-ray photoemission spectroscopy) and IR (infrared) analyses of poly(3-methylthienylene) films, electrochemically or chemically redoped0 with various chemical species at varying doping levels, have been investigated. On the basis of these results, the major chemical species of dopants have been identified. As a results, the dopant content was determined and the poly(3-methylthienylene) films were classified as light or heavy by doping level. The conductivity ranged from about 10^?12 to 10₂ S cm^?1 for all the films investigated. The conductivity and the activation energy of conduction for the heavily-doped films vary as a function of the dopant content, independent of the different chemical species of dopants. In particular, a sudden change is observed in the dependence of activation energy on dopant content. This sudden change may be associated with the semi-conductor-metal transition. Furthermore, it is shown that the specific absorption bands in the infrared are induced by the doping, intensified with increasing dopant uptake and accompanied by an increase in conductivity.     

Humidity-dependent characteristics of thin film poly(3,4-ethylenedioxythiophene) field-effect transistor

π-Conjugated poly(3,4-ethylenedioxythiophene) (PEDOT) based field-effect transistors (FETs) were fabricated in this study. A thin PEDOT layer (thickness ≈500 nm) with the desired pattern was formed as an active and a gate electrode by a vapor polymerization of 3,4-ethylenedioxythiophene (EDOT) on the photolithographically patterned ferric p-toluenesulfonate (FTS) oxidant layer. Crosslinked poly(vinyl cinnamate) (PVCN) insulating layer was formed by spin-coating and UV crosslinking. The currents (I_ds) of the PEDOT active channel decreased with increasing gate bias (V_g), implying p-type FET. The dc conductivities (σ_dc) and I_ds of the PEDOT active channel were measured as a function of V_g under various relative humidities (RHs) ranging from 0% to 55%. The σ_dc and the I_ds of the PEDOT channel rapidly decreased with increasing positive V_g under humid conditions, while those of the PEDOT channel showed no change with V_g in vacuum, i.e. 0% RH. The threshold gate bias, which is defined as the onset of the curve of I_ds versus V_g, rapidly decreased with increase of RH. The moisture absorbed in the PEDOT active channel may assist the dedoping of the system by the screening and/or the relative separation of constituent ions from PEDOT chain upon applying a positive V_g. When the positive V_g was removed (V_g = 0), the σ_dc of the channel recovered slowly and a relatively long relaxation time was observed, which implies that the PEDOT active layer was slowly redoped. For the PEDOT based FET, we observed the moisture assisted dedoping and the redoping processes of the PEDOT channel upon applying and removal of positive V_g under the humid conditions.