Electrochemically prepared poly(3-methylthienylene) films doped with iodine

Electrochemically prepared poly(3-methylthienylene) films doped with iodine have been investigated and the relationship between their conductivity and iodine content was studied. The conductivity of the films with various iodine contents was obtained in accordance with an Arrhenius equation with an activation energy equal to 0.17 to 0.033 eV. The highest conductivity was 5 S cm^?1. The activation energy, which is dependent on the iodine content, shows discontinuous change, as is the case with polyacetylene doped with iodine. The relationship between conductivity and structure of the poly(3-methylthienylene) films will be discussed.     

Photoluminescence and electroluminescence properties of poly(9-vinylcarbarzole) doped with anthracence derivatives containing bis(ethynylphenyl oxadiazole) or bis(vinylphenyl oxadiazole) substituents

The photoluminescence (PL) and electroluminescence (EL) properties of two novel light-emitting anthracence derivatives containing bis(ethynylphenyl oxadiazole) or bis(vinylphenyl oxadiazole) substituents (ANOs) blended with poly(9-vinylcarbazole) (PVK) are characterized. The energy transfer process in the blends is discussed. By employing 2,5-bis(5-tert-butyl-2-benzoxazolyl) thiophene (BBOT) and tris(8-hydroxyquinoline) aluminum (Alq3) as electron transporting layers (ETLs) in the EL devices, remarkable improvements in EL efficiency were observed. The effect of the transporting layer on the EL intensity of the devices is also discussed.     

Magnetic properties of undoped and doped poly[(3-methoxy)4,6-toluene] (P3mt)

The magnetic properties of two types of poly[(3-methoxy)4,6-toluene] (P3mt₁ and P3mt₂) are studied before and after doping with iodine or organic acids (CF₃COOH or CH₃SO₃H) in a range of temperature varying from 110 to 460 K. Under 250 K and independent of the state, the magnetic susceptibility χ obeys Curie law dependence. Up to this temperature, χ is governed by a Pauli law contribution. This fact can be related to localized or delocalized spin. Furthermore, iodine doping induces distortion in the polymers that affects the ESR line distribution. In the case of organic acids doping process, a hyperfine structure with hyperfine coupling constant values between 2.2 and 2.8 G is observed. As the spin concentration decreases, we deduce that in the case of P3mt₂, there is a de-doping process.     

Exciton fusion and charge-carrier generation in poly(di-n-hexylsilane)

We have observed charge-carrier generation in the long-wavelength tail of the first electronic transition in poly(di-n-hexylsilane), which varies as the square of the intensity of the incident light and as the absorption coefficient raised to a power somewhat greater than two. We discuss two mechanisms involving exciton fusion for generating carriers.     

Highly crystalline and soluble dodecylbenzene sulfonic acid doped poly(o-toluidine)

Dodecylbenzene sulfonic acid (DBSA) doped poly(o-toluidine) (POT) was synthesized by oxidative polymerization technique. The optical, structural, morphological, thermal and electrical properties of the POT-DBSA have been investigated. It was found that conducting emeraldine salt of POT-DBSA is stable in chloroform. X-ray diffraction showed that the POT-DBSA is a highly crystalline polymer due to formation of H-bonding across chains. The scanning electron micrograph reveals a flaky like feature with few globular structures and the size of the grain was about 3 μm. The highest conductivity of POT-DBSA was found to be 1.88 × 10^?3 S/cm at 1:1 molar ratio of oxidant to o-toludine and at 0.18 M of DBSA. Schottky diode based on POT-DBSA was fabricated using Al as Schottky contact and Cu as an Ohmic contact. The junction parameters including ideality factor and barrier height of the diode was 3.0 and 0.989 eV, respectively.     

Photovoltaic devices based on a novel poly(phenylene ethynylene) derivative

A novel poly(phenylene ethynylene) derivative containing benzothiadiazole (BT) co-monomer (PPE-BT) was synthesized, characterized and used for photovoltaic devices. Photovoltaic devices of ITO/PEDOT-PSS/pristine PPE-BT/Ba/Al and ITO/PEDOT-PSS/PPE-BT+PCBM (1/4 w/w)/Ba/Al were fabricated and their photovoltaic performances were measured and discussed. The energy conversion efficiency and incident photo-current conversion efficiency of photovoltaic device based on PPE-BT+PCBM reached 0.022% (78.2 mW/cm², AM1.5) and 1% (391 nm), respectively. Its photosensitivity reached 3.1 mA/W, which is almost one order of magnitude higher compared to that of the pure PPE-BT. The electroluminescence of pristine PPE-BT was almost completely quenched when it was blended with PCBM.     

Studies of the photocurrent generation performances from a series of amphiphilic bis-chromophore zinc complexes and correlation between photocurrent generation performance and molecular structure

A systematic study of the photocurrent generation (PCG) performances from seven analogues of bis-hemicyanine dye chromophore cations ionically combined with a bivalent zinc anion, bis-(2-thione-1,3-dithiol-4,5-dimerapto) zinc, has been made under the same conditions in order to discuss the influence of molecular structure on PCG performance. The coincidence of the action spectra of the PCG with the absorption spectra of the monolayer LB films on indium–tin oxide (ITO) electrodes indicate that the hemicyanine analogue chromophore cations in the bis-chromophore complex are the photoelectric active moieties which is responsible for the PCG for each analogue. The results also demonstrate that these bis-chromophore zinc complexes have larger quantum yield than their corresponding iodide salts. The correlation between PCG capability and the molecular structure of hemicyanine dye chromophore cation has been established. This correlation is valuable in leading to systematic improvement in performance and new molecule design with high quantum efficiency.     

Enhanced electron injection and electroluminescence in poly(N-vinyl carbazole) film doped with ammonium salt

We demonstrated that the electron injection and electroluminescent (EL) properties of poly(N-vinyl carbazole) (PVCz) can be dramatically improved by lightly doping with tetra-n-butylammonium tetrafluoroborate (Bu₄NBF₄). The device used in this study was an ITO/PVCz:Bu₄NBF₄(95:5 in mol)/Al. The EL spectrum of this device was similar to that of an undoped device, and the peak wavelength was 402 nm. The maximum EL intensity of this device was 407 cd/m² at 11.5 V at 486 mA/cm² which is higher by three orders of magnitude than that of an undoped device.     

Particle induced X-ray emission (PIXE) and radiochemistry study of poly(pyrrole) doped with toluenesulfonate or polystyrenesulfonate anions

Poly(pyrrole) films have been prepared at constant current using two different doping ions (i.e., toluenesulfonate ions or polystyrenesulfonate ions). Particle induced X-ray emission experiments show that incorporation is reversible with toluenesulfonate anions: when the films are reduced in 0.1 mol dm⁻³ KNO₃ solutions, all the anions incorporated during the synthesis are released. With polystyrenesulfonate ions, however, the incorporation is irreversible. It is likely that such films have cation exchanging properties. This phenomenon has been studied using barium ions, the incorporation of which was monitored using a radiochemical method.     

Morphology and physico-electrochemical properties of poly(aniline-co-pyrrole)

Copolymers of aniline (An) and pyrrole (Py), poly(aniline-co-pyrrole), have been prepared by a conventional chemical oxidative polymerization from monomer mixtures of various compositions, with ammonium persulfate (APS) as the oxidant and hydrochloric acid as the dopant, and the morphologies and physico-electrochemical properties of the poly(aniline-co-pyrrole) have been investigated. Poly(aniline-co-pyrrole) prepared with more polyaniline (PANI) or polypyrrole (PPy) component have similar morphologies, structures, thermal and electrochemical performances, and the relative dosage (molar ratio) of An and Py monomers during the polymerization is crucial to the properties of the resulting poly(aniline-co-pyrrole). More monomer applied in the polymerization of An and Py mixtures would result in products with similar properties to the individual homopolymer of that monomer, while poly(aniline-co-pyrrole) prepared from equimolar An and Py monomer displays unique properties. The conductivity is a non-linear function of chemical composition, and this chemical heterogeneity might lead to the broad DSC curves and various morphologies of the poly(aniline-co-pyrrole) copolymers.     

Alkali doped poly(vinyl alcohol) for potential fuel cell applications

Optical transparent, chemically stable alkaline solid polymer electrolyte membranes were prepared by incorporation KOH in poly(vinyl alcohol) (PVA). The distributions of oxygen and potassium in the membrane were characterized by XRD and SEM–EDX. It is demonstrated that combined KOH molecules may exist in the PVA matrix, which allow it to be an ionic conductor. In particular, the chemical and thermal stabilities were investigated by measuring changes of ionic conductivities after conditioned the membrane in various alkaline concentrations at elevated temperatures for 24 h for potential use in fuel cells. The membranes were found very stable even in 10 M KOH solution up to 80 °C without losing any membrane integrity and ionic conductivity due to high dense chemical cross-linking in PVA structure. The measured ionic conductivity of the membrane by AC impedance technique ranged from 2.75 × 10^?4 S cm^?1 to 4.73 × 10^?4 S cm^?1 at room temperature, which was greatly increased to 9.77 × 10^?4 S cm^?1 after high temperature conditioning at 80 °C. Although, a relatively higher water uptake, the methanol uptake of this membrane was one-half of Nafon 115 at room temperature and 6 times lower than that of Nafion 115 after conditioned at 80 °C. The membrane electrolyte assembly (MEA) fabricated with PVA–KOH in direct methanol fuel cell (DMFC) mode showed an initial power density of 6.04 mW cm^?2 at 60 °C and increased to 10.21 mW cm^?2 at 90 °C.     

Synthesis and optical properties of poly(thiophene-fluorene) copolymers with benzothiazole moiety

Poly[9,9-dihexylfluorene-co-(benzothiazol-2-yl)thiophene-co-9,9′-spirobifluorene] (PF_xB_yS_z) were synthesized by palladium-catalyzed Suzuki coupling reaction. PF_xB_yS_z were characterized by FT-IR, elemental analysis, and ¹H NMR. All the copolymers showed decomposition temperatures above 400 °C and glass transition points above 180 °C, suggesting that these materials had excellent thermal stability. As the benzothiazolylthiophene content in copolymers was increased, the band gaps of copolymers decreased. All the copolymers exhibited fluorescence peaks in the visible region, and the energy transfer from fluorene to benzothiazolylthiophene units were observed.     

Synthesis and electrical properties of poly(p-azoarylene) films

Polymers and copolymers containing p-azoarylene and p-azoxyarylene groups were synthesized by oxidative coupling of various aromatic diamines. Films were cast directly from the reaction mixtures or from the polymer solutions. The films were n-doped by sodium naphthalide or p-doped by iodine. They showed electrical conductivities of 10⁻⁴ ohm⁻¹ cm⁻¹ to 10⁻⁵ ohm⁻¹ cm⁻¹.     

Synthesis and properties of chemically coupled poly(thiophene)

We describe the synthesis and physical properties of poly(thiophene) with a molecular weight of approximately 4000 consisting of 46 – 47 thiophene rings (184 – 188 carbons along the backbone). The pristine polymer exhibits an ESR line similar to that of cis-(CH)_x; the small number of unpaired spins is consistent with relatively high-quality material. The electrical conductivity can be increased by nearly ten orders of magnitude to values in excess of $\text{10 Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ upon partial oxidation by AsF₅. The magnitude and temperature dependence of the thermopower of the doped polymer (24 mol%) are consistent with metallic behavior. The decrease in conductivity as the temperature is lowered and the magnitude of π at room temperature apparently result from the macroscopic transport being limited by interparticle contacts.     

Electrochemical preparation and properties of poly(3-methoxy-2,5-thiophenediyl) and poly(3-methylthio-2,5-thiophenediyl)

Soluble and conductive poly(3-methylthio-2,5-thiophenediyl) and poly(3-methoxy-2,5-thiophenediyl) films were prepared by the electrochemical polymerization of 3-(methylthio)thiophene (MTT) and 3-methoxy-thiophene (MOT), respectively. The polymers were identified from their i.r. spectra and found to be soluble in chloroform, propylene carbonate (PC), dimethyl sulfoxide (DMSO) and 1-methyl-2-pyrrolidinone (NMP). When doped, they were soluble in PC, DMSO and NMP. Cast films could be obtained from their solutions. The degrees of polymerization of poly-MTT and poly-MOT were 7.4 and 79, respectively. The vis-near i.r. specta of either polymer solution had characteristic peaks due to bipolarons. The doped poly-MTT solution became undoped after four days in air. The doped poly-MOT solution was stable for a few months, and the conductivity of the pressed pellet of doped poly-MOT did not change for as long as 11 months. With regard to differences in the absorption spectra between the films and solutions of the undoped state, the films had bands at longer wave-length than the solutions. The shifts may possibly have been due to internal rotation about single bonds, probably occurring more freely in solution than in films. Solid-state samples retained the coplanar configuration. In cyclic voltammograms, the oxidation potential of poly-MOT was lower than 0 V versus Ag/Ag⁺. It is thus evident that the doped state of poly-MOT is stable in air.     

Electronic transport in doped poly (3,4-ethylenedioxythiophene) near the metal-insulator transition

The temperature dependences of the conductivity and magnetoconductivity of poly(3,4-ethylenedioxythiophene) doped with PF₆, BF₄ and CF₃SO₃ in the metallic and critical regimes have been studied. Doped films exhibit a weak temperature dependence of the resistivity, ϱ(T), with the characteristic resistivity ratio ϱ_r = ϱ(1.4 K)/ϱ(291 K) = 1.5–20; i.e. close to the metal-insulator transition. For metallic samples (ϱ_r<2.1) prepared with each of the dopants, the sign of the temperature coefficient of resistivity (TCR) changes from negative to positive below 10 K; the temperature of the resistivity maximum, T_m, decreases with increasing ϱ_r. For samples with ϱ_r ~ 20, the power-law temperaturedependence characteristic of the critical regime of the metal-insulator transition is observed, with ϱ(T) ~ T^−0.6. High magnetic fields induce the transition from positive to negative TCR for all metallic samples with ϱ_r < 2.1 and decrease the low-temperature conductivity for samples with ϱ_r > 2.1. In both cases (negative and positive TCR), the low-temperature conductivity of metallic samples is well described by a T^1/2 dependence, both in the presence of a magnetic field and with the magnetic field equal to zero. The magnetoconductance of samples in metallic and critical regimes is negative, Isotropic, and, for metallic samples, exhibits H² and H^1/2 dependences at low and high magnetic fields, respectively. The results for metallic samples are explained as resulting from the influence of electron-electron interactions on the lowtemperature conductivity.     

Optical properties of highly oriented poly(p-phenylene-vinylene)

A review of recent results on the complex refractive index determination of oriented poly(p-phenylene-vinylene) (PPV) by polarized near-normal-incidence reflectance, transmittance and ellipsometry measurements is presented. In particular, the new experimental data obtained for highly stretch-oriented films of PPV and the results of correlated quantum-chemical calculations on the same polymer will be reported and discussed with the purpose of clarify the controversial assignment of the electronic transitions of PPV and its derivatives.     

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.