Impact of hydrogen bonds in polyaniline.AMPSAn/acid solutions

Water concentration in polyaniline (PANI)/acid solutions containing 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPSA) significantly changes the solubility of PANI and the stability of its solutions. By varying trace amounts of water, we investigated the impact of hydrogen bonds (H-bonds) on PANI chain conformation in solutions of AMPSA/dichloroacetic acid (DCAA) or AMPSA/orthophosphoric acid. UV–vis–NIR spectral changes of these PANI solutions reveal that a competition between H-bond formation and protonation among PANI, AMPSA and water is an on-going process. The H-bonds between the PANI and AMPSA molecules can cause a large red shift in the π_b → π_q electron transition (the quinoid peak) from ∼630 nm into the near IR (NIR) region. Absent protonation peak (410–490 nm) and blue color of the solution suggest that the H-bond interaction, instead of protonation, is sufficient to cause PANI chains to adopt an “expanded coil” chain conformation in the PANI.AMPSA_n/DCAA or H₃PO₄ solutions. Protonation leads to the gelation of PANI solutions. The kinetic mechanism of protonation of the PANI.AMPSA_n/DCAA solutions is studied. The activation energy of protonation in the PANI.AMPSA_0.6/DCAA solutions is ∼60 kJ/mol.     

GPC characterization of emeraldine base in NMP containing ionic liquids

Strong aggregation between chains of polyaniline (PANI) emeraldine base (EB) molecules dissolved/dispersed in N-methyl-2-pyrrolidinone (NMP) results in a multi-modal molecular weight distribution in gel permeation chromatograph (GPC) results, regardless of how low the concentration of EB is. The addition of a salt, such as lithium chloride (LiCl), is known to improve EB solubility in NMP by deaggregating the polymer chains. However, we have found that ionic liquids, such as 1-methyl-3-butyl imidazolium tetrafluoroborate ([BMIM][BF₄]) or 1-methyl-3-ethyl imidazolium tetrafluoroborate ([EMIM][BF₄]), not only have less impact on the EB chain conformation than LiCl does, but also deaggregate the EB molecules more effectively. A mono-distributed GPC peak is obtained for EB (M_w up to 3 × 10⁵ g/mol) dissolved in the NMP/ionic liquid solutions. Therefore, the EB molecular weight distribution is characterized more accurately by using the NMP/ionic liquid solution than the NMP/LiCl solution.     

Polyaniline emeraldine base in N-methyl-2-pyrrolidinone containing secondary amine additives: B. Characterization of solutions and thin films

Secondary amines are added to emeraldine base (EB)/N-methyl-2-pyrrolidinone (NMP) solutions to stabilize the EB solution. However, amines can interact with the EB molecule either by physical interaction, such as with the hydrogen bond (H-bond), or by chemical reaction. Several amines with different basicity and geometry were investigated. The UV–VIS–NIR, FT-IR, GPC, and TGA results reveal that secondary amines, due to their different basicity and molecular size, can chemically degrade EB in two different ways. Secondary amines with strong basicity and small size, such as azetidine (AZ) and pyrrolidine (PY), attack both the quinoid ring and the NC site in the EB backbone immediately. The attacked EB not only loses its conjugated structure due to ring substitution, but also loses its molecular weight because the chain breaks down. Secondary amines with moderate or strong basicity and large geometry, such as heptamethyleneimine (HPMI), reduce most of the quinoid ring to form a ring-substituted material. The final product loses its conjugated structure, but its molecular weight does not appreciably change. However, amines with weak basicity, such as 2-methyl-aziridine (2MA), form H-bonds with EB but do not appreciably degrade the EB structure.     

Synthesis,characterization, and photovoltaic properties of diketopyrrolopyrrole-oligothiophene/fullerene dyads

Low-band-gap dyad molecules containing diketopyrrolopyrole (DPP) chromophore and hexathiophene were designed and synthesized in combination with C₆₀ and C₇₀ derivatives as the electron acceptors. The effect of alkyl side chains in the donor parts on film morphology, thermal properties, and optical properties were investigated by X-ray diffraction analysis, differential scanning calorimetry, UV–vis absorption spectroscopy, and fluorescence spectroscopy. The donor part with a shorter alkyl side chain showed better packing of the π-plane and an enhancement of absorption in the longer-wavelength region, which led to higher J_SC of organic solar cells. The use of C₇₀ as the electron acceptor led to stronger absorption in the visible region, resulting in improved external quantum efficiency and J_SC compared with those of the C₆₀ derivatives. The single-component solar cell of the dyad with the methyl side chains and C₇₀ derivative showed the power conversion efficiency of 0.84% with a relatively high J_SC of 4.4 mA cm⁻² under AM 1.5 illumination (100 mW cm⁻²).     

Optical and electrical characteristics of poly(3-alkylthiophene) and polydiphenylamine copolymers: Applications in light-emitting devices

In this work, poly (3-methylthiophene) (P3MT) or poly (3-octylthiophene) (P3OT) films were synthesized electrochemically with polydiphenylamine (PDFA), in layers and blended copolymers, in non-aqueous media through the oxidation of the monomers, using a standard three-electrode cell in acetonitrile with 0.100 mol L⁻¹ LiClO₄. The polymeric thin films were deposited on platinum plates for optimal quality control of the process. The electrochemical behaviors of as-prepared and partial dedoped films obtained by these methods was verified by cyclic voltammetry (CV) and have been characterized by UV–vis reflectance, resonance Raman, electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. Based on data obtained by UV–vis reflectance spectroscopy, it was possible to characterize the chemical species in the polymer matrix using the resonant Raman method. Both Raman and PL spectra results led to the characterization of three structures (aromatic, semi-quinone and quinone forms of thiophene rings) which formed the homopolymers and copolymers chain. The EPR measurements were taken to quantify the semi-quinone species stabilization at 298 and 77 K temperatures. The ionization potential (I_P), electron affinity (E.A.) and gap energy (E_g) parameters were determined based on the technical analyses carried out.     

A facile and inexpensive method for the preparation of conducting polyaniline–clay composite nanofibers

Hybrid nanofibers constituted by polyaniline doped with phosphoric acid (PAniPh) and two different clays: pristine montmorillonite (MMT-Na⁺) and organoclay functionalized with amino undecanoic acid (MMT-COOH), were successfully prepared by employing a very simple procedure based on previous swelling the clay in anilinium salt solution followed by in situ polymerization under static conditions and low [acid]/[aniline] molar ratio. The nanocomposites were characterized by X-ray diffraction (XRD), field emission-scanning electron micrograph (FEG-SEM), transmission electron microscopy, Fourier transform-infrared (FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, electrical conductivity and thermal gravimetric analysis (TGA). Nanocomposites containing around 12% of clay resulted in conducting nano-fibers with ramose structure and higher electrical conductivity than pure PAniPh. The extended conformation was also confirmed from UV–vis spectrum. The best surface conductivity (2.3 S/cm) and highest extended conformation were observed for the PAniPh/MMT-COOH nanocomposite.     

Synthesis and nonlinear optical characterization of new poly{2,2′-(3,4-didodecyloxythiophene-2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]}

A new donor–acceptor type poly{2,2′-(3,4-didodecyloxythiophene-2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]} (P) was synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. The polymerization was carried out using chemical polymerization technique. The optical and charge-transporting property of the copolymer was investigated by UV–vis, fluorescence emission spectroscopic and cyclic voltammetric studies. The copolymer shows UV absorption maxima at 375 nm and displays bluish-green fluorescence in DMF solution. Its electrochemical band gap was determined to be 2.07 eV. The nonlinear optical (NLO) properties of the copolymer was investigated at 532 nm using single beam Z-scan and degenerate four-wave mixing (DFWM) techniques with nanosecond laser pulses. The copolymer exhibits strong optical limiting behavior due to effective three-photon absorption (3PA). Values of the effective 3PA coefficient (γ), third-order nonlinear susceptibility (χ⁽³⁾) and figure of merit (F) have been calculated.     

Organic photosensitizers with N-carboxymethyl pyridinium acceptor/anchoring group for dye-sensitized solar cells

Four new organic dyes with N-carboxymethyl pyridinium as electron acceptors/anchoring groups were designed and synthesized. The optical and electrochemical properties were characterized by UV–vis, fluorescence spectroscopy and cyclic voltammetry. The absorption spectra of the four pyridinium dyes were in the range of 450–650 nm. The dye with triphenylamine as the electron donor shows a solar-energy-to-electricity conversion efficiency (η) of 2.33% in comparison with the reference Ru-complex (N719 dye) with a η value of 5.45% under the same experimental conditions. The dye with phenoxazine as the electron donor gives broad IPCE spectra in the range of 400–750 nm. All these new dyes are simple in structure, very easy to synthesize, and gives high V_oc.     

Modification of graphite oxide nanoparticles prepared via electrochemically oxidizing method

Graphite oxide nanoparticles (GONPs), prepared via electrochemically oxidizing technique, were chemically reduced by hydrazine hydrate in water medium. The electrical conductivity of the samples showed an improvement by three orders of magnitude from 1.38 × 10⁻⁶ s cm⁻¹ (before reduction) to 1.02 × 10⁻³ s cm⁻¹ (after reduction). UV–vis measurement was used to explained the restoration of the conducting conjugated networks in graphite nanoparticles. The hydrophilic GONPs or their reduced samples could be further organically modified, using cetyltrimethylammoniumbromide (CTAB) as a modifier, turned to a hydrophobic nanoparticles which could form homogeneous and stable dispersion in toluene, and other organic media.     

The role of oxygen in the interaction of emeraldine base polyaniline with Cu(II) or Fe(III) ions in NMP solution

The influence of molecular oxygen in the interactions of emeraldine base form of polyaniline (EB-PANI) with Fe(III) or Cu(II) ions in 1-methyl-2-pyrrolidinone (NMP) solutions has been investigated by UV–vis–NIR, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies. Through the set of spectroscopic results it was possible to rationalize the role of O₂ and to construct a scheme of preferential routes occurring in the interaction of EB-PANI with Fe(III) or Cu(II). Solutions of 4.0 mmol L⁻¹ EB-PANI with 0.8, 2.0 and 20 mmol L⁻¹ Fe(III) or Cu(II) ions in NMP were investigated and the main observed reactions were EB-PANI oxidation to pernigraniline (PB-PANI) and EB-PANI doping process by pseudo-protonation, or by a two-step redox process. In the presence of O₂, PB-PANI is observed in all Fe(III)/EB solutions and EB-PANI doping only occurs in solutions with high Fe(III) concentrations through pseudo-protonation. On the other hand, emeraldine salt (ES-PANI) is formed in all Fe(III)/EB solutions under N₂ atmosphere and, in this case, doping occurs both by the pseudo-protonation and two-step redox mechanisms. In all Cu(II)/EB solutions PB-PANI is formed both in the presence and absence of O₂, and only for solutions with high Cu(II) concentrations doping process occurs in a very low degree. The most important result from EPR spectra was providing evidence for redox steps. The determined Cu(II) signal areas under oxygen are higher than under N₂ and, further, the initial metal proportions (1:2:20) are maintained in these spectra, indicating that Cu(I) formed are re-oxidized by O₂ and, so, Cu(II) ions are being recycled. Consistently, for the solutions prepared under nitrogen, the corresponding areas and proportions in the spectra are much lower, confirming that a partial reduction of Cu(II) ions actually occurs.     

The influence of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture

We examine the effects of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-additive concentration, molecular weight, and specimen elongation on the temperature-dependent electronic transport properties of polyaniline films prepared with AMPSA in the presence of a great excess of a formic and dichloroacetic acid (DCAA) solvent mixture. The AMPSA-additive dependent resistivity and thermopower are reported for free-standing PANI:AMPSA_x (M_w=200,000 g mol⁻¹) films (x=0.1–0.5) in the temperature range from 2 to 325 K. The low-temperature data indicate that these samples are just on the insulating side of a disorder-induced metal–insulator (M–I) transition (dρ/dT<0), and that thermal motion at elevated temperatures is sufficient to produce a metallic state (dρ/dT>0) at room temperature. Transport occurs via variable-range hopping (VRH) for temperatures below 200 K, with hopping parameters that are a strong function of x; increased AMPSA concentration decreases the resistivity and moves the samples towards the M–I phase boundary. There is a minimum in the resistivity for all samples at a temperature T_min that is also doping dependent. Stretch orientation of PANI:AMPSA_0.5 films, prepared with higher molecular weight PANI (M_w=300,000 g mol⁻¹), along the resistivity measurement direction decreases the room-temperature resistivity at the expense of a more insulating low-temperature state. The T_min values of both stretched and unstretched PANI:AMPSA_0.5 films are pushed below 200 K, which reflects reduced disorder in film processed with higher molecular weight polyaniline. These results reflect an evolution in the underlying inhomogeneous mesoscopic disorder present in doped conducting polymers.     

Study of the interconversion of polyaniline oxidation states by optical absorption spectroscopy

The polyaniline (PANI) bases can be classified in three distinct oxidation states: leucoemeraldine (LB), the totally reduced form, emeraldine (EB), the half oxidized form, and pernigraniline (PB), the totally oxidized form. The oxidation state varies continuosly from the leucoemeraldine to the pernigraniline base with addition of oxidant agent, and vice-versa with addition of reductor. In this work, we studied the polyaniline oxidation state interconversion using ultraviolet/visible (UV–vis) optical absorption spectroscopy. We utilized PANI and a derived form of it, poly(o-methoxyaniline) (POMA). For oxidation, we used ammonium peroxydisulfate and, for reduction, ascorbic acid, both in solutions of N-methyl-2-pyrrolidinone (NMP). We observed isosbestic points in the spectra when a base converted to another, and this indicates that one base converts directly to another in one step at molecular level, without passing through any intermediate forms. Using UV–vis optical absorption curves, we obtained a method simpler than others cited in literature to estimate the oxidation states. The method consisted in obtaining calibration curves which give the unknown oxidation states of polymeric samples (PANI and POMA).     

Synthesis of electrochemically and thermally stable amorphous hole-transporting carbazole dendronized fluorene

A novel amorphous hole-transporting carbazole dendrimer, 2,7-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-9,9-bis-n-hexylfluorene (G2CF), was synthesized by a divergent approach involving bromination and Ullmann coupling reactions. G2CF showed UV–vis absorption bands at 304 and 332 nm in chloroform solution and the photoluminescence spectra showed a maximum peak at 373 nm in a bluish-purple region. Differential scanning calorimetry (DSC) and cyclic voltammetry (CV) analysis revealed G2CF was an electrochemically and thermally stable amorphous material with a high glass transition temperature (T_g) of 237 °C. The organic light-emitting device having the structure of ITO/G2CF/Alq₃/LiF:Al exhibited a bright green emission with a maximum luminescence of 11,000 cd/m² at 16 V and a turn-on voltage of 5.4 V.     

Temperature dependence of the resistance of self-assembled polyaniline nanotubes doped with 2-acrylamido-2-methyl-1-propanesulfonic acid

Hollow polyaniline (PANi) nanotubes doped with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) have been synthesized and their electrical resistance measured as a function of temperature. The average length of the nanotubes was in the range 2–5 μm and the average diameter was in the range 200–400 nm. Longer reaction times did not affect the morphology of the nanotubes. The resistance of AMPSA doped nanotubes were measured as a function of temperature and compared to emeraldine base PANi doped with AMPSA in the solid state. Dissolving the PANi nanotubes in dichloroacetic acid leads to better polymer chain ordering.     

Synthesis of two benzo[1,2-b:3,4-b′]dithiophene-based conjugated polymers with different side chains and their applications in photovoltaic devices

Two D–A conjugated polymers (named PBDTC₆DBT and PBDTC₁₀DBT) with benzo[1,2-b:3,4-b′]dithiophene (BDT) as donor and 4,7-dithiophen-2,1,3-benzothiadiazole (DBT) as acceptor, were designed and synthesized. PBDTC₆DBT and PBDTC₁₀DBT have hexyl and decyl as side chains in the DBT units, respectively. The polymers were characterized by spectroscopic (NMR and UV–vis) methods, GPC, DSC and cyclic voltammetry. In order to study the photovoltaic properties of the two conjugated polymers, photovoltaic devices with the configuration of ITO/poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS)/polymer:[6,6]-phenyl C₆₁-butyric acid methyl ester (PC₆₁BM)/LiF/Al, were fabricated, in which PBDTC₆DBT or PBDTC₁₀DBT acted as electron donor in active layers. According to the experimental data, when the blend ratio of PBDTC₆DBT and PC₆₁BM reached 1:2, the best photovoltaic properties among the PBDTC₆DBT-based devices were obtained, and the open-circuit voltage, the short-circuit current density and the power conversion efficiency were measured to be 0.63 V, 6.18 mA/cm² and 1.86%, respectively. As to PBDTC₁₀DBT-based devices, the maximum of power conversion efficiency reached 0.99% with the blend ratio of PBDTC₁₀DBT and PC₆₁BM being 1:2. PBDTC₁₀DBT and PBDTC₆DBT were both promising donor candidates in the application of polymer solar cells.     

CO sensor based on polypyrrole functionalized with iron porphyrin

Polypyrrole (PPy) was chemically functionalized with 5,10,15,20-tetraphenyl-21H,23H-porphyrin iron(III) chloride (FeTPPCl) with special interest on noxious carbon monoxide (CO) gas in ppm level. Controlled functionalization of PPy was achieved with incorporation of various concentrations of porphyrin. The resulted semiconducting material was well characterized by different techniques such as UV–vis spectroscopy, FTIR, GFAAS, XRD, and EDAX. The functionalized polypyrrole material on interdigitated electrode was experienced an immediate increase in resistance when exposed to carbon monoxide gas at very low concentration. The CO gas interacted very fast with the FeTPPCl functionalized PPy at room temperature (RT) and then slowly saturated. The response of these materials was not unidirectional, but reverses to the original resistance level when CO was removed from the test chamber. The highest response factor (ΔR/R₀ × 100) and lowest response time (t₅₀) obtained are 12 and 169 s, respectively. An optimum level of doping (1 mol% of FeTPPCl) was established for the highest sensitivity and the detection level is as low as 100 ppm.     

Preparation and fluorescent properties of europium (III) complexes with β-diketone ligand and 2,2-dipyridine or 1,10-phenanthroline

The β-diketone ligand, 1-(4-methoxyphenyl)-3-phenylpropane-1,3-dione (MPPD), and its binary Eu(III) complexes Eu(MPPD)₃, ternary complexes Eu(MPPD)₃·Bipy with 2,2-dipyridine (Bipy) and Eu(MPPD)₃·Phen with 1,10-phenanthroline (Phen) were prepared. The complexes were characterized with by elemental analysis, FT-IR, ¹H NMR, UV–vis absorption, thermogravimetric analysis (TGA), ESI-MS and fluorescence spectroscopic techniques. TGA results showed that these complexes have good thermal stability. The emission spectra for complexes 2–4 exhibited the characteristic emission bands that arise from the ⁵D₀ → ⁷F_J (J = 0–4) transitions of the europium ion in solid state and chloroform solution. Based on the emission spectra in solid state, the Eu(III) ion could be sensitized efficiently by the ligands to some extent, in particular, in the ternary system, the secondary ligands Bipy and Phen acting as a light-harvesting center was involved in the highly efficient energy transfer process. In addition, the experimental intensity parameters, Ω₂ and Ω₄ were calculated from the fluorescence emission spectra. The radiative decay rate A_rad, the nonradiative rates A_nrad, the lifetime (τ) and the luminescent quantum yield (η) were determined and analyzed.     

A simple polyol synthesis of silver metal nanopowder of uniform particles

Silver metal has been synthesized in form of a finely divided loose nanopowder, 10–30 nm particle sizes, using a simple polyol process. In hot water, polymer molecules of polyvinyl alcohol (PVA) induce Ag⁺ → Ag reaction as a weak reducer (suitable to control the final particle size), forming a nanofluid of Ag nanoparticles in situ dispersing in part of PVA molecules. Ag nanoparticles do not aggregate much when casting a viscous Ag–PVA nanofluid (hot) onto a substrate in thin laminates or films. Freestanding Ag–PVA films could be obtained of 1–5 mm thickness after drying at room temperature. Dried sample can be easily peeled from a silicate glass substrate. As small as 5–10 mm Ag–PVA pieces were heated in air in order to recollect Ag nanoparticles by burning off the polymer. At 300–400 °C, Ag–PVA disintegrates and encounters combustion in air, resulting in a pure Ag-powder. As analyzed by X-ray diffraction, a single crystalline phase of an Fm3m cubic crystal structure formed. Lattice parameter a = 0.4071 nm and density ρ = 10.61 g/cm³ compare well the bulk values a = 0.4086 nm and ρ = 10.50 g/cm³.     

Rheological characterization of 2-acrylamido-2-methyl-1-propanesulfonic acid-doped polyaniline solution

The rheological properties of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-doped polyaniline (PAni) using dichloroacetic acid (DCA) as solvent were systematically studied using parallel-plate rotational rheometer. The influence of PAni/AMPSA concentration, PAni molecular weight, shear rate, temperature and time on the apparent viscosity was measured and analyzed. At certain shear rate (about 0.03–1 s^?1, in the second region), PAni/AMPSA solution presents typical shear-thinning behavior, and PAni/AMPSA concentration and PAni molecular weight obviously affected the rheological behaviors of PAni/AMPSA solution. By temperature sweeps, it was found that the apparent viscosity of PAni/AMPSA solution decreased with the increase of temperature, and the solution became gel after 80–90 °C. More importantly, a predominant transition temperature at about 55 °C was observed in the PAni/AMPSA solutions, suggesting a structural transition at this temperature. The results of the rheological stability of PAni/AMPSA solution at different concentration and molecular weight by monitoring the viscosity change with the time at 30 and 60 °C verified that the higher temperature might be responsible for the quick gelation of the PAni solution. In addition, the non-Newtonian exponent and the apparent viscous flow activation energies of PAni/AMPSA solution has been calculated and discussed as well.     

Electrochemical,optical and electrochromic properties of imine polymers containing thiophene and carbazole units

New imine polymers containing thiophene and carbazole moiety were synthesized by using both chemically oxidative in the presence of FeCl₃ and electrochemically oxidative process. While UV–vis, FT-IR, ¹H- and ¹³C NMR techniques were used for the structural characterization, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values were determined by size exclusion chromatography (SEC). The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels, electrochemical (E^′g)$({E^{\prime }}_g)$ and optical band gap (E_g) values were calculated by using the results of cyclic voltammetry and UV–vis absorption spectroscopy measurements, respectively. Spectroelectrochemical measurements were carried out against the changes in the optical properties of conducting polymers upon voltage changed. Also the yellow color of film changed to green color with applied potential. Conductivities of these polymers were determined by using four-point probe technique. It was seen that the conductivities were increased by iodine doping.