13C NMR and Fourier transform infrared study of electrochemically prepared polythienylene film

The ¹³C NMR and Fourier transform infrared (FTIR) spectra of an electrochemically prepared polythienylene film have been obtained. The polythienylene film displays only two sharp absorption bands, at 124.8 and 136.5 ppm downfield from TMS (tetramethylsilane) in the ¹³C NMR, these being attributable to the carbon atoms in the β-position and the α-position, respectively, relative to the sulfur atom of poly(2,5-thienylene). The polythienylene film also shows a sharp absorption band at 789 cm^?1 in the IR, which is definitely ascribable to the C-H out-of-plane vibration of poly(2,5-thienylene). The polythienylene film will be shown to have a highly defined structure with a dominance of poly(2,5-thienylene).     

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.     

Structural characterization of amorphous hydrogenated-carbon nitride (aH-CNx) film deposited by CH4/N2 dielectric barrier discharge plasma: C, H solid state NMR, FTIR and elemental analysis

The chemical composition and bond structure of polymer like amorphous hydrogenated carbon nitride (aH-CN_x) thin films was studied by solid-state ¹³C and ¹H MAS NMR spectroscopy, FTIR spectroscopy and elemental analysis. The hydrogenated CN_x film was deposited on Si (100) substrate by CH₄/N₂ gas mixture dielectric barrier discharge (DBD) plasma. The broad ¹H signals obtained even at 33 kHz spinning speed with spinning side bands indicates the existence of a large proton proportion in the film. The ¹H and ¹³C signals are strongly broadened due to homo- and heteronuclear dipolar couplings and also due to amorphous nature of the deposited film. The local structure of the amorphous aH-CN_x film is dominated by C-C and C-N single bonds i.e. carbon is mainly in the sp³ hybridized state. The Fourier Transform infrared (FTIR) spectroscopy of the film indicates the typical regions for -C≡N, -(CO), -NH, vibrations together with overlapping NH and OH stretching bonds. CH₃ and C-N groups as well as species with CN conjugated double bonds are present in the deposited CN_x film. From elemental analysis it is obtained that the composition of the film is (in wt.%): C: 61.8, H: 8.4, N: 17.7.     

Ions transport and self-doping in layer-by-layer conducting polymer films

The self-doping mechanism for charge transport is investigated in layer-by-layer (LBL) films from two conducting polymers, namely poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA). The efficiency of charge intercalation, defined as the ratio between the charge and the mass change, is twice for the POMA/PTAA LBL film in comparison with a cast POMA film. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated with experiments using a quartz crystal microbalance. The doping efficiency for LBL film is the same, i.e., 3.93 × 10⁻⁴ and 3.56 × 10⁻⁴ g/C for the Li⁺ and (C₂H₅)₄N⁺ doped films, and is different for the cast POMA film, i.e., 11.3 × 10⁻⁴ for Li⁺ and 6.45 × 10⁻⁴ g/C for (C₂H₅)₄N⁺. Therefore, once no significant differences in the intercalation mechanism are observed when different cations, Li⁺ or (C₂H₅)₄N⁺, are used with the LBL films, this indicates that the self-doping mechanism is controlled by the exchange of anions.     

Iron doping effects on the high-resolution 13C NMR spectra of solid poly(para-phenylene)

A comparative study of the electrical conductivity, electron spin density and ¹³C high-resolution solid-state NMR linewidth of FeCl₃-doped poly(para-phenylene) (PPP) was made as a function of Fe³⁺ concentration. It is concluded that the NMR linewidth changes are related to the interaction between bipolarons in the polymeric chain.     

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.     

Experimental studies of n-doped (CH)x: D.c. electrical conductivity

The d.c. electrical conductivity of n-doped (CH)_x was studied as a function of the doping level at 25°C. The dopants were sodium-naphthalene, lithium and sodium benzophenone dianionic salts in tetrahydrofuran (THF). Details of the experimental procedure are described.It was discovered that the THF vapour pressure present in the atmosphere in contact with the doped film drastically increases the film conductivity, at low doping levels. This may be due to an effect of the solvation state of cations.Conductivity measurements were also performed at very low doping levels (evaluated from metallic infrared bands) on (CHNa_y)_s, (CDNa_y)_x and (CDK_y)_x. A mobility value of 4 × 10^?6 cm^2/rmVs was deduced for 57% trans-(CHNiny)_x.     

Bridged polysilsequioxane adsorption materials containing phosphonic acid residues

Reactions of hydrolytic polycondensation of bis(triethoxysilane) [(C₂H₅O)₃Si]₂C₂H₄ (or [(C₂H₅O)₃Si]₂C₆H₄) and functional agent (C₂H₅O)₃Si(CH₂)₂P(O)(OC₂H₅)₂ (alkoxysilanes molar ratio of 2: 1 and 4: 1, fluoride ion catalyst and ethanol solvent) yielded powder-like xerogels that contained phosphonic acid residues in the surface layer. Their treatment with boiling concentrated hydrochloric acid resulted in transformation of functional groups ≡Si(CH₂)₂P(O)(OC₂H₅)₂ into acid groups ≡Si(CH₂)₂P(O)(OH)₂. The methods of IR, ¹H MAS NMRm and ¹³C, ²⁹Si, ³¹P MAS NMR spectroscopy showed the following (1) The surface layer in the initial xerogels contains not only phosphorus functional groups, but also some non-hydrolyzed ethoxysilyl groups as well as silanol groups. (2) The hydrochloric acid treatment of the initial xerogels causes the hydrolysis of not only ethoxy groups in the phosphonic acid residues, but also most residual ethoxysilyl groups. (3) Vacuum drying of xerogels after acid treatment forms ≡Si(CH₂)₂P(O)(OH)-OSi≡ links in their surface layer (not more than 20% of phosphorus-containing groups). (4) According to ²⁹Si CP MAS NMR spectroscopic data, boiling acid treatment relatively enriches the xerogel structure T² and T³ units and accounts for the higher rigidity of the hybrid framework. These units also account for retention of the porous structure in these xerogels over time, while most initial xerogels have porous structures that collapse in 12–18 months of storage. The acid-treated xerogels were attributed to microporous adsorbents (having specific surface area of 620 to 760 m²/g). According to the AFM data, both initial and acid-treated xerogels contain almost spherical aggregates of the primary particles (globules).     

A comparative study on liquid-state photoelectrochemical cells based on poly(3-hexylthiophene) and a composite film of poly(3-hexylthiophene) and nanocrystalline titanium dioxide

A comparative study was done between liquid-state photoelectrochemical cells (PECs) consisting of photoactive electrodes of poly(3-hexylthiophene), P3HT, and a composite film of nanocrystalline titanium dioxide (nc-TiO₂) and P3HT. The nc-TiO₂/P3HT based device shows better performance with an open-circuit voltage of 0.51 V, a short-circuit current of 0.31 mA/cm², and a fill factor of 0.51 when illuminated with white light intensity of 100 mW/cm². The IPCE% obtained at 550 nm for P3HT based device was 0.18% while for that of the nc-TiO₂/P3HT based device was 4%. In P3HT based devices, P3HT showed its p-type behavior while in nc-TiO₂/P3HT based devices, P3HT acted as a sensitizer to nanocrystalline TiO₂.     

Bridge polysilsesquioxane xerogels with a bifunctional surface layer of the ≡Si(CH<Subscript>2</Subscript>)<Subscript>3</Subscript>NH<Subscript>2</Subscript>/≡Si(CH<Subscript>2</Subscript>)<Subscript>3</Subscript>SH composition

Xerogels with a bifunctional surface layer of the ≡Si(CH₂)₃NH₂/≡Si(CH₂)₃SH composition are synthesized by hydrolytic co-polycondensation of bis(triethoxy)silane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and two trifunctional silanes, namely, 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. Using IR, ¹H MAS NMR, and ¹³C CP/MAS NMR spectroscopic techniques, it is shown that in addition to complexing groups, the surface layer also contains water, silanol groups that are involved in the hydrogen bond formation and also residual ethoxysilyl groups. According to ²⁹SiCP/MAS NMR spectroscopic data, the degree of polycondensation of synthesized xerogels exceeds 80%. It is found that the use of 1,2-bis(triethoxysilyl)ethane as the structuring agent in place of tetraethoxysilane allows one to synthesize bifunctional xerogels with the highly developed biporous structure (S _sp = 607–680 m²/g, V _c = 1.38–1.47 cm³/g, d = 2.9–3.1 and 18.3 nm). Changing the ratio structuring-silane/functionalizing-silane-mixture from 2: 1 to 4: 1 in the reaction system has virtually no effect on the porous structure parameters of final xerogels.     

Effect of γ irradiation on the electrical properties of trans-polyacetylene

Trans-polyacetylene powder, prepared with the help of a Ti(OC₄H₉)Al(C₂H₅)₃ catalyst mixture, was exposed to γ irradiation up to a dose of 1 Mrad. An investigation, using IR, ¹³C NMR and DSC techniques, showed that no essential structural changes occurred during irradiation.The conductivity of undoped material markedly decreases on irradiation. The thermopower slightly increases. Both features suggest that a reduction in number of charge carriers, rather than a mobility decrease, is responsible for the conductivity decrease. The results are analysed in the framework of Kivelson's theory describing hopping between charged and neutral solitons.     

FTIR studies of charged photoexcitations in regio-regular and regio-random poly(3-alkylthiophene) films

We have studied the low energy photo-induced absorption (PA) band of photo-generated polarons in a variety of poly(3-alkylthiophene) (P3AT) films which including regio-regular and regio-random stereo orders, different length of alkyl side group, and various film preparation techniques. In addition to the traditional one-dimensional (1D) polaron PA bands, we observed quasi two-dimensional excitations (DP) in regio-regular P3AT films, where the polymer chains self-organize to form 2D lamella structures. Due to increased interlayer and interchain coupling, the two plaron energy levels split by 2Δ (≈2t_⊥), resulting in two allowed optical transitions where the lower energy band (DP₁) dominates and red-shifts into the mid infrared range. The DP₁ band blue-shifts when the length of the alkyl side group increases, or when using lower boiling point solvent, or when preparing films at higher temperature.     

Anisotropic conductivity–temperature characteristic of solution-cast poly(3-hexylthiophene) films

For the purpose of developing a positive temperature coefficient (PTC) device, thin films of poly(3-hexylthiophene) (P3HT) were prepared by solution-cast from chloroform. In the present work, the P3HTs of high molecular weight (M_w) with various regioregularities were employed, and the structure anisotropy and the temperature dependence of conductivities in directions parallel (σ_∥) and perpendicular (σ_⊥) to the film surface were investigated. For highly orientated P3HT films, the temperature dependence of σ_⊥ was found to reflect an amorphous character of charge hopping along this direction. However, the σ_∥ decreased greatly above 50 °C, which was attributed to a decrease in the in-plane π-stacking caused both by the melting of crystallized side chains and the enhanced side-chain disturbance with increasing temperature. Different charge transport mechanisms were proposed to explain the anisotropic conductivity–temperature characteristics observed in the two directions. The high conductivity in the parallel direction was deteriorated significantly by thermal recycles, probably due to a reduction of the orientation degree of P3HT crystallites in the bulk film, rather than a change of conjugated length of polymer backbone. A reversible PTC effect was observed for the P3HT film with a high M_w and medium regioregularity in the perpendicular direction, which suggested that the high M_w was more important than the high regioregularity to design the thin film PTC devices based on the soluble P3HT films.     

Self-healing protective films prepared on zinc by treatments with cerium(III) nitrate and sodium phosphate

Chromate-free, self-healing protective films were prepared on a surface of zinc electrode previously treated in a solution of cerium(III) nitrate Ce(NO₃)₃ by coverage of the surface with a layer of sodium phosphate Na₃PO₄. The self-healing ability of the film was examined by polarization measurements of the electrode after scratching the surface with a knife-edge crosswise and immersed in an aerated 0.5 M NaCl solution for many hours and by observation of pit formation at the scratches. A thin film containing 0.0552 mg/cm² of Na₃PO₄·12H₂O prepared on the electrode previously treated in 1×10⁻³ M Ce(NO₃)₃ at 30 °C for 30 min and dried at 90 °C for 23 h was highly self-healing and protective against corrosion of zinc in 0.5 M NaCl at the scratches. No pit was detected at the scratches on the electrode coated with this film after immersion for 72 h.     

Multiferroic BiFeO<Subscript>3</Subscript> thick film fabrication by aerosol deposition

BiFeO₃ (BFO) multiferroic materials in the crystalline phase require very delicate processing conditions. In order to fabricate a high quality BFO thick film, aerosol deposition (AD) was employed and the phase evolution and multiferroic properties of the film were investigated for different annealing temperatures. A BFO thick film annealed at 500 °C had a dielectric constant of 80 at 1 kHz and possessed ferroelectric characteristics. At an applied electric field of ∼900 kV/cm, the remaining polarization and coercive field (E_c) were approximately 7.5 μC/cm² and 370 kV/cm, respectively. In addition, the BFO thick film fabricated via AD and annealed at 500 °C showed weak ferromagnetic behavior between −1250 Oe and +1250 Oe and was saturated at the higher magnetic field strength, showing ferromagnetic behavior.     

Preparation and luminescent characteristics of Sr3RE2(BO3)4:Dy (RE = Y, La, Gd) phosphors for white LED

Dysprosium-activated Sr₃RE₂(BO₃)₄ (RE = Y, La, Gd) phosphors were synthesized by a high temperature solid-state reaction method. The phase uniformity of the phosphors was characterized by X-ray powder diffraction (XRD) and the luminescence characteristics were investigated. The excitation spectra at 575 nm emission show strong spectral bands in the region of 300-500 nm. The emission spectra of the phosphors with 365 nm excitation show three bands centered at 484 nm, 575 nm and 680 nm, which originate from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The effect of Dy³⁺ concentration on the emission intensity of the phosphors was investigated. The fluorescence decay curves for ⁴F_9/2 → ⁶H_13/2 excited at 365 nm and monitored at λ_em of 575 nm were measured. The decay times decreased slowly with increasing Dy³⁺ doping concentration due to a trap capturing to resonance fluorescence transfer of the activated ions and due to the exchange interactions between activated ion pairs. In order to determine the type of interaction between activated ions, the concentration dependence curves (lg(I/x) versus lg x) of Sr₃RE₂(BO₃)₄:Dy³⁺ (RE = Y, La, Gd) were plotted. The concentration quenching mechanism of the ⁴F_9/2 → ⁶H_13/2 (575 nm) transition of Dy³⁺ is the d-d interaction. All results indicate these phosphors are promising white-color luminescent materials.     

Solution processable organic electro-phosphorescent iridium complex based on a benzothiazole derivative

We have synthesized a new solution processable iridium complex, di[2-(4′-octyloxyphenyl) benzothiazole]iridium(III)acetoacetone, [(OPBT)₂Ir(acac)], based on benzothiazole derivative for organic electro-phosphorescent devices. The synthesized molecule was identified by ¹H NMR and ¹³C NMR, and readily soluble in common organic solvents such as chlorobenzene. The UV–visible absorption and photoluminescence properties of pristine [(OPBT)₂Ir(acac) thin film as well as poly(N-vinylcarbzole) (PVK) thin film doped with the iridium complex were studied. The maximum UV–visible absorption and photoluminescence (PL) spectra are found to be at 337 nm and 547 nm, respectively. We have fabricated phosphorescent organic light-emitting devices using the ITO/PEDOT:PSS (40 nm)/PVK:(OPBT)₂Ir(acac) (40 nm)/Balq (40 nm)/LiF (1 nm)/Al (80 nm) configuration with the iridium complex as a triplet emissive dopant in poly(N-vinylcarbazole) (PVK) host. The electroluminescence (EL) devices showed greenish yellow light emission with maximum peak at 551 nm. Especially, the maximum external quantum and current efficiency of 1 mol% doped device were 1.74% and 4.89 cd/A, respectively.     

Effect of annealing temperature on ferroelectric properties of （Bi, Nd）4（Ti, V）3O12 thin films

Thin films of Nd^3＋/V^5＋-cosubstituted bismuth titanate, （Bi3.sNd0.5）（ Ti2.96V0.04）O12 （BNTV）, were fabricated on the Pt（111）/Ti/SiO2/Si（100） substrates by a chemical solution deposition technique and annealed at different temperatures of 650, 700, 750 and 800 ℃. The surface morphology and ferroelectric properties of the samples were studied in detail. The result shows that the film annealed at 800 ℃ indicates excellent ferroelectricity with a remanent polarization of 2Pr=40.9 i.tC/cm^2, a coercive field （Ec） of 114 kV/cm at an applied electrical field of 375 kV/cm. The substitution of Ti-site ion by V^5＋ ions could improve the upper limit of the optimal annealing temperature by decreasing the space charge density in BNT thin film. Additionally, the mechanism concerning the dependence of ferroelectric properties of BNTV thin films on the annealing temperature was discussed.     

Characterization of poly(isothianaphthene) derivatives and analogs by using solid-state 13C NMR

The combination of several options of a multipurpose ¹³C CP/MAS solid-state pulse sequence allows the characterization of insoluble poly(isothianaphthene) (PITN) derivatives and analogs. In order to improve solubility and processability of low bandgap polymers, poly (5-tert.butylisothianaphthene) and poly(5,6-dihexoxyisothianaphthene) have been synthesized and analyzed. The same chemistry also allows for the synthesis of poly(2,3-dihydro-1H-indene) and poly (isoindole). Based on model compounds, a proper ¹³C NMR assignment enables one to predict the geometric structure (aromatic versus quinoid) of these conducting polymers.     

A proton magnetic relaxation study on pyrolysates of polyacrylonitrile (PAN) fibres: Motion of electrons

Polyacrylonitrile (PAN) fibres heat treated at temperatures between 400 and 800 °C (PAN400-PAN800) have been studied by means of proton NMR. The spin-lattice relaxation rate (T₁⁻¹) was measured as a function of NMR frequency over a wide range (4–300MHz). T₁⁻¹ was found to show the singular dependence upon frequency characteristic of the low-dimensional (one- and two-dimensional) diffusive motion of electrons. A distinct change of the dimensionality of the electronic motion from one dimensional to two dimensional was observed in PAN500. In addition, the dependence of T₁⁻¹ on the heat-treatment temperature (HTT) is in accordance with that of the unpaired electron spin number measured by ESR. It was interpreted in terms of polaron and bipolaron formation.