On the energy transfer from a polymer host to the rhenium(I) complex in OLEDs

Photoluminescence and electroluminescence of PVK films doped with fac-[ClRe(CO)₃(bpy)], bpy = 2,2′-bipyridine, are investigated. Photoluminescence spectra of spin-coated PVK films (λ_exc = 290 nm) exhibit a broad band centered at 405 nm. As the concentration of dopant increases, the polymer emission is quenched and a band at 555 nm appears (isosbestic point at 475 nm). In OLEDs with ITO/PEDOT:PSS/PVK/butylPBD/Al architecture doped with fac-[ClRe(CO)₃(bpy)], the polymer host emission is completely quenched even at the lowest concentration of dopant. The electroluminescence spectra of the devices show that there is an efficient energy transfer from the host to the dopant, which exhibits a very intense emission at 580 nm.     

Microstructural studies and electrical properties of Mg-doped SrTiO3 thin films

The structure–property relations of Mg-doped SrTiO₃ (ST) sol–gel thin films deposited on Pt/TiO₂/SiO₂/Si substrates have been investigated in order to determine the effect that Mg dopants have on the dielectric properties of SrTiO₃. It has been predicted that Mg-doped SrTiO₃ should exhibit a dielectric anomaly similar to that observed recently in Bi doped SrTiO₃ but, to date, no polar state has been reported. It has been suggested that this may relate to the low solubility of Mg on the A-site in bulk ceramics (<0.05 at.%). However, for Sr_1−xMg_xTiO₃ (SMT) (x ⩽ 0.30) films annealed at 750 °C, all Mg ions were accommodated in the perovskite lattice and for SMT films annealed at 900 °C, the solubility limit of Mg was x = 0.10, above which a Mg-rich ilmenite second phase was observed. Irrespective of the higher solid solubility limit of Mg in the ST lattice for sol–gel ST films compared to equivalent ceramics, no ferroelectric or relaxor phase transition was observed, refuting previous predictions for this dopant.     

Self-assembling into interconnected nanoribbons in thin films of hairy rod poly(9,9-di(2-ethylhexyl)fluorene): Effects of concentration,substrate and solvent

This study utilizes atomic force microscopy to investigate the self-assembling behaviors from dilute solution into thin film of a well-known conjugated polymer, poly(9,9-di(2-ethylhexyl)fluorene) (PF2/6). We have found that the structures of nanoscale aggregates depend on various experimental parameters including concentration, substrate and solvent. The self-assembling of PF2/6 from 0.05 mg/mL solution in toluene onto SiO_x/Si substrate results in the formation of interconnected nanoribbons with thickness and width of about 20 and 150 nm, respectively. Varying polymer concentration and type of substrate (SiO_x/Si or mica) significantly affects the nanoscale structures. The change of solvent to chlorobenzene, a slightly more polar solvent with slower evaporation rate, causes the growth of ribbon width to micron size with slight increase of the thickness. When the solvents with higher evaporation rate (i.e. chloroform and dichloromethane) are used, densely packed nanoribbons are obtained. Its width also grows to micron size. The measurements of UV/vis absorption and photoluminescence spectra detect some discrepancies in pattern, reflecting the variation of local chain organization within thin films prepared by using different solvents.     

Effect of various parameters on the conductivity of free standing electrosynthesized polypyrrole films

Electrical characteristics of polypyrrole films electrodeposited in different aqueous electrolyte solutions including p-toluenesulfonate, naphtalenesulfonate, nitrate, tetrafluoroborate, and perchlorate anions were investigated using the Van der Pauw procedure. The polymer films were synthesized by electrochemical oxidation at a fixed potential. Experimental parameters including the pyrrole concentration, electrolyte, applied potential and substrate were shown to affect the electrical conductivity σ of polypyrrole films. Since the substrate contributes significantly to the overall conductivity of polypyrrole-coated electrodes, the results obtained with free standing polymer films appeared more reliable. The results indicated that the p-toluenesulfonate doped PPy film showed the highest average conductivity (σ_293 K = 4.5 × 10⁵ S m^?1) whereas the perchlorate doped one produced the lowest of all the films prepared (σ_293 K = 2 × 10⁴ S m^?1).     

The role of solvent on the doping of polyaniline with Fe(III) ions

The products formed from the reaction of emeraldine base polyaniline (EB-PANI) with Fe(III) ions in N-methyl-pyrrolidone (NMP), dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol media have been investigated using UV–VIS–NIR and resonance Raman (λ₀ = 632.8 and 1064 nm) spectroscopies. Through these results it was verified that the different PANI forms in solution can be formed by the suitable choice of the solvent. The behavior of Fe(III)/EB-PANI in different solvents was rationalized in terms of the interactions among Fe(III) ions, EB-PANI and solvent. In basic NMP, DMA and DMF media, the reaction of Fe(III) with EB-PANI yields EB-PANI doping giving ES-PANI and/or the EB-PANI oxidation to PB-PANI. The formation of ES-PANI is favored in DMF while PB-PANI is formed in a greater extension in NMP and DMA. In acidic m-cresol, only ES-PANI is produced in Fe(III)/EB-PANI solutions indicating the important role played by the solvent in the nature of the product.     

Polypyrrole-polyethylene glycol conducting polymer composite films: Preparation and characterization

The preparation and characterization of polypyrrole-polyethylene glycol (PPy-PEG) composite films are reported in this present paper. The polypyrrole-polyethylene glycol composites were synthesized by electrochemical method, using p-toluene sulfonate as a dopant in aqueous medium. The composite films were synthesized with various concentration of PEG and were characterized by optical microscopy, x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, photoacoustic spectroscopy and electrical conductivity measurement. Both the electrical conductivity and thermal diffusivity exhibited the highest values with the process condition of 0.2 M pyrrole, 0.1 M p-toluene sulfonate and 1×10⁻³ M PEG at 1.2 V (versus SCE). The optical microscopy of PPy-PEG shows the globular surface morphology. The XRD results demonstrated that PPy-PEG composite films are amorphous. The FTIR result reveals the successful incorporation of PEG into the PPy structure forming PPy-PEG composite films.     

A cyclopentadithiophene/thienopyrroledione-based donor–acceptor copolymer for organic solar cells

A new cyclopentadithiophene/thienopyrroledione-based donor–acceptor copolymer (P1) was synthesized using a microwave-assisted Stille coupling procedure and was compared to a known benzodithiophene-based copolymer using the same thienopyrroledione acceptor monomer (PBDTTPD). Cyclopentadithiophene-based copolymers have been known to exhibit lower band gaps than their corresponding benzodithiophene-based counterparts. The polymer showed excellent solubility at room temperature in chlorinated solvents. The absorption onset for P1 is close to 740 nm as compared with ～685 nm for PBDTTPD, corresponding to an optical band gap of 1.67 eV, which is 0.15 eV lower than PBDTTPD. The photovoltaic characteristics of the polymer were determined under AM1.5 illumination. The P1:PCBM BHJ device showed a high V_oc (0.92 V) and J_sc (8.02 mA/cm²) as well as a good PCE (2.43%), while the best device with 2% solvent additive gave a PCE of 3.47%.     

Preparation of organo-soluble polyanilines in ionic liquid

A method for preparation of organo-soluble polyaniline (PANI) is described. Oxidative coupling polymerization of anilium chloride with ammonium persulfate in a new ionic liquid, 2-hydroxyethyl ammonium formate (HAF), gives organo-soluble polyaniline with appreciable molecular weights (M_w = 86,400). Interestingly polyaniline (PANI) prepared by this method is highly soluble in many organic solvents such as acetone, tetrahydrofurane, dioxane, dimethyformamide and N-methyl, 2-pyrrolidinone. Thin films of PANI prepared at 0 °C (by solvent casting) show reasonable conductivities (up to 37.0 S cm⁻¹) when doped with p-toluene sulfonic acid.     

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.     

Comparative study: The effects of solvent on the morphology,optical and structural features of regioregular poly(3-hexylthiophene):fullerene thin films

In this report the effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C₆₀ films. The polymer blend films spin coated from faster evaporating, non-aromatic solvents demonstrated an improved ordering and optical absorption in P3HT and blended films, indicating that the limited solubility of P3HT:C₆₀ in a marginal solvent can lead directly to optimal morphologies on the films. The PL quenched by a factor of 3 after blending the P3HT with C₆₀ in a 1:1 wt. ratio using CB, xylene, DCB, and toluene as solvents, indicating a partially charge transfer from P3HT to C₆₀. A complete reduction in the PL intensity was observed in the film spin-coated from chloroform.     

Electrochemical synthesis of novel conducting polymer composite: Polypyrrole–pentacyanonitrosylferrate

With a view to develop conducting polymer film of high electroactivity, pentacyanonitrosylferrate (PCNFe) doped polypyrrole (PPY) composite films are prepared using cyclic voltammetry deposition method. The PPY–PCNFe composite is characterized by FTIR, TEM and TGA analysis. The electroactivity of PPY–PCNFe composite film is studied in 3 mM KCl (common electrolyte) solution. Two redox pairs at E_1/2 = ?0.59 V and 0.02 V due to redox behavior of polymer and dopant anions respectively are observed. The electroactivity study reveals the existence of two types of PCNFe dopant anions in the polymeric film: one form is loosely held and prone to easy removal from the polymer matrix whereas the other form is strongly bound to polymer backbone and prone to electrochemical redox reaction by movements of electrons. The high electroactivity of the film is attributed to the movements of ionic species into and out of the polymeric film as well as movements of electron.     

Synthesis of sulfonated polyaniline by polymerization of the aniline heterodimer 4-aminodiphenylamine-2-sulfonic acid

The aniline heterodimer 4-aminodiphenylamine-2-sulfonic acid has been polymerized in aqueous ammonium persulfate solution to yield a new form of sulfonated polyaniline (SPAn). This polymer, obtained as a green powder, is soluble in aqueous base (violet solution) and polar solvents (green solution, turning blue on standing). Its FTIR, UV–VIS and EPR spectra are quite similar to those of SPAn obtained by direct ring-sulfonation of polyaniline. The room temperature dc conductivity of the polymer is about 1.3×10⁻⁵ S/cm, indicative of considerable disorder in the sample. Cyclic voltammetry in 1.0 M HCl shows two redox peaks at E_1/2,1=0.50 V and E_1/2,2=0.68 V against Ag/AgCl electrode, characteristic of SPAn.     

Polyaniline,a dynamic block copolymer: key to attaining its intrinsic conductivity?

Photoluminescence studies of spun films of polyaniline base (emeraldine oxidation state) show that films prepared from NMP solution in air having a relative humidity between 43±2 and 57±2% (21°C) exhibit photoluminescence at 401 nm, which persists when the films are held in a dynamic vacuum. Films prepared from NMP solution containing water show similar behavior to those prepared in the above humidity range. When protonated (“doped”) with HCl the above photoluminescence disappears and is replaced by a photoluminescence peak at 467 nm. The reverse behavior occurs on deprotonation with NH₃ vapor, the 467 nm peak disappearing and the 401 nm peak reappearing. These results, together with photoluminescence studies on the phenyl/phenyl end-capped tetramer of aniline in both the emeraldine and leucoemeraldine oxidation states, lead to the conclusion that in solution the emeraldine base is a dynamic block copolymer in which reduced (benzenoid/amine) and oxidized (quinoid/imine) units are constantly interchanging positions via a tautomeric (hydrogen migration) process between nitrogen atoms. This process is promoted by water. The resulting production of long sequences of the reduced and oxidized units, which separate long sequences of the emeraldine base, persist when the NMP solvent is removed, resulting in microphase segregation of these sequences in the solid film. Since only the emeraldine base sequences can be doped by acids, the conductivity of the doped film is less than that of its predicted intrinsic conductivity.     

A novel low band gap conjugated polymer based on N-substituted dithieno[3,2-b:2′,3′-d]pyrrole

Poly{[N-dodecyl-dithieno(3,2-b:2′,3′-d)pyrrole-2,6-diyl]-alt-[2,1,3-benzothiadiazole-4,7-diyl]} (PBTDTP) was successfully prepared via Stille coupling. The new polymer is soluble in common organic solvents such as chloroform (CHCl₃), tetrahydrofuran (THF) and o-dichlorobenzene. Compared with N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole (DTP) homopolymer, the maximum absorption of PBTDTP was red-shifted approximately 40 nm. The optical band gap of the polymer in film state is 1.55 eV calculated from the onset of absorption spectrum. The cyclic voltammetry measurements of the polymer depicted a HOMO energy level of ?5.0 eV and a LUMO energy level of ?3.3 eV of PBTDTP. This work demonstrates that this newly synthesized polymer is a promising p-type material for application in bulk hetero-junction organic solar cells.     

Characterization of poly(N-alkylanilines) by Raman spectroscopy

Thin films of poly(N-alkylaniline) were synthesized in acidic aqueous solution and in mixtures of aqueous and organic solvents. The polymer films (alkyl = methyl, ethyl, propyl and butyl) were characterized by Raman spectroscopy with the excitation wavelengths of 514.5, 632.8 and 780 nm. The main Raman bands have been characterized for the leucoemeraldine, emeraldine and pernigraniline oxidation states between −0.2 and 0.8 V (vs. Ag|AgCl). This fundamental study shows that the structure of the half-oxidized emeraldine form contains quinoid units, which supports the commonly accepted oxidation and reduction scheme of poly(N-alkylanilines).     

Large magnetoresistance observed in facing-target sputtered Ni-doped CNx amorphous composite films

A series of amorphous Ni-doped CN_x films with ∼23 at.% Ni were fabricated using facing-target sputtering at different nitrogen partial pressures (P_N). The films were composed of ∼1–4 nm Ni-rich particles embedded in a CN_x matrix and turn from ferromagnetic at low temperatures to superparamagnetic at room temperature. The largest negative magnetoresistance (MR = [R(H) − R(0)]/R(0)) reaches −59% at a P_N of 4% and a temperature of 3 K. With a decrease of P_N from 4% to 0%, the electrical transport mechanism changes from tunneling to variable-range hopping and the maximum MR drops from ∼59% to ∼3.8%. The MR–H curves show a weak saturation trend in a high-field regime and the MR–T curves follow the relation of log|MR| ∝ −T below 20 K for all the films, despite the difference in transport mechanism. The origin of the large MR (−59%) can be ascribed to a spin-related high-order tunneling process.     

Oxidative polymerization of 4-[(4-phenylazo-phenyimino)-methyl]-phenol catalyzed by horseradish peroxidase

Schiff base derivate 4-[(4-phenylazo-phenyimino)-methyl]-phenol (4-PPMP) monomer was synthesized by condensation reaction and the chemical structure of the monomer has been characterized by UV–vis, FT-IR, ¹H NMR spectroscopies. 4-PPMP readily dissolves in 1,4-dioxane, THF, DMF, diethyl ether, chloroform and DMSO. Its solubility in methanol and ethanol is much lower. Enzymatic oxidative polymerization of azobenzene derivate 4-[(4-phenylazo-phenyimino)-methyl]-phenol using horseradish peroxidase (HRP) in the presence of hydrogen peroxide as catalyst and oxidizing agent was carried out in various solvents (acetone, methanol, ethanol, N,N-DMF, and 1,4-dioxane) and phosphate buffers (pH 6, 6.8, 7, and 7.2) at room temperature. Studies have shown that a black polymer having a melting point of 290 °C was successfully produced in good yields by utilizing aqueous 1,4-dioxane as the solvent at pH 6. Poly(4-[(4-phenylazo-phenyimino)-methyl]-phenol) P(4-PPMP) shows good solubility in 1,4-dioxane, DMF and DMSO but it is only sparingly soluble in chloroform, THF, methanol and ethanol. P-(4-PPMP) is insoluble in diethyl ether. Characterization of P-(4-PPMP) was carried out via UV–vis, FT-IR, ¹H NMR, elemental analysis and SEC measurements. The number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) of the polymer were determined to be 7970.4, 8146.2 and 1.02 g mol^?1, respectively. FT-IR and ¹H NMR studies confirmed the presence of phenylene and oxyphenylene units with in the polymer backbone. The optical band gaps (E_g) of 4-PPMP and P-(4-PPMP) were calculated as 3.69 and 3.36 eV, respectively.     

Electrochemical synthesis of self-doped polyaniline in fluorosulfonic acid/acetonitrile solution

Electrochemical formation of self-doped sulfonated polyaniline (SPAN) was carried out in acetonitrile-containing anhydrous fluorosulfonic acid (FSO₃H). Fluorosulfonic acid was used as both sulfonation reagent for aniline and also as supporting electrolyte. The degree of sulfonation of the polymer was controlled by varying FSO₃H and aniline concentrations while the film is being deposited. Different dry conductivity values for the polymer (1.24–14.6 S/cm) were measured depending on the degree of sulfonation of polyaniline. Polychromic behavior of SPAN (transparent yellow–green–dark blue) was observed when the cyclic voltammograms were taken between −0.30 and +1.90 V (vs. Ag/AgCl, saturated) during the growth of polyaniline film. The polymers having different degrees of sulfonation were found to be soluble in basic aqueous solution, dimethyl sulfoxide (DMSO) and N-methylpyrrolidone (NMP). SPAN was characterized by elemental analysis, FT-IR spectroscopy, UV–visible spectroscopy and cyclic voltammetry.     

Transport studies of NH4NO3 doped methyl cellulose electrolyte

This work reports on the transport properties of NH₄NO₃ doped methyl cellulose (MC) polymer electrolyte. The polymer electrolyte films were prepared by the technique of solvent casting. The highest room temperature conductivity of MC doped with 25 wt.% NH₄NO₃ is 2.10 ± 0.37 × 10^?6 S cm^?1. Conductivity–temperature relationship obeys the Vogel–Tamman–Fulcher (VTF) rule from which the glass transition temperature, T_g was evaluated. The mobility, μ and number density of charge carrier, n were calculated using the Rice and Roth model.     

Synthesis and characterization of low-bandgap copolymers based on dihexyl-2H-benzimidazole and terthiophene

A series of new semiconducting polymers with 3-(hexyloxy)thiophene, 2,2-dihexyl-2H-benzimidazole (HBI) and thiophene units was synthesized using Stille polymerization. These random copolymers show good solubility at room temperature in organic solvents owing to the long alkyl chain in new acceptor, 2,2-dihexyl-2H-benzimidazole. In HBI, the sulfur at 2-position of 2,1,3-benzothiadiazole (BT) unit was replaced with the carbon to make a highly soluble electron deficient moiety while keeping the 1,2-quinoid form of BT unit. The spectra of the solid films show absorption bands with maximum peaks at about 408–526 nm and the absorption onsets at 550–692 nm, corresponding to band gaps of 1.79–2.25 eV. The onset wavelengths of the absorption spectra in thin films exhibit a gradual red-shift with decreased amount of dihexyl-2H-benzimidazol unit, that is, from 550 nm with PHOTDTHBI-9 to 692 nm with PHOTDTHBI-1. Under white light illumination (AM 1.5 G, 100 mW/cm²), the device with PHOTDTHBI-3:PCBM blend demonstrated a V_OC value of 0.36 V, a J_SC value of 1.20 mA/cm², and a FF of 0.37, leading to the efficiency of 0.16%.