Synthetic Metals (v.158, #6)

Cross-linkable aromatic amines as materials for insoluble hole-transporting layers in light-emitting devices by S. Lengvinaite; J.V. Grazulevicius; S. Grigalevicius; B. Zhang; J. Yang; Z. Xie; Lixiang Wang (213-218).
A series of cross-linkable aromatic amines has been synthesized by the multi-step synthetic rout. Full characterization of their structure by 1H NMR-, IR- and mass spectrometry is presented. The synthesized materials were examined by various techniques including differential scanning calorimetry, thermogravimetry, UV and electron photoemission spectrometry. The electron photoemission spectra of the layers showed their ionisation potentials of 5.1–5.2 eV. One of the derivatives was used for the preparation of insoluble hole-transporting layers by photoinduced polymerization. The layers obtained were tested in multilayer light-emitting diodes. The device-containing hole-transporting layer of PEDOT/cross-linked network exhibited the best overall performance with a turn-on voltage of 5 V, a maximum photometric efficiency of 2.8 cd/A and a maximum brightness of ca. 5600 cd/m2.
Keywords: Aromatic amine; Cross-linkable material; Ionisation potential; Light-emitting diode;

Electroluminescence of (styrene-co-acrylic acid) ionomer/conjugated MEH-PPV blends by Rafael F. Cossiello; Ali Cirpan; Frank E. Karasz; Leni Akcelrud; Teresa D.Z. Atvars (219-225).
This work reports the electroluminescence of poly[2-methoxy-5(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and poly(styrene-co-acrylic acid-co-1-pyrenylmethyl methacrylate) (SAA) blends in ratios from 0 to 100 wt.% in mass of MEH-PPV. The styrene-co-acrylic copolymer was synthesized with 3 mol% of acrylic acid units to simultaneously enhance blend miscibility and charge transport in MEH-PPV. The morphology was studied using epifluorescence microscopy and scanning electron microscopy in which the pyrenyl-labeled copolymer is used to enhance microscopic contrast. Device performances were compared: those using MEH-PPV have a turn-on voltage of 3.5 V, luminance of 500 cd/m2 and current density of 430 mA/cm2 at 5 V, while MEH-PPV blended with 50 wt.% styrene–acrylic copolymer showed a turn-on voltage of 2.5 V, a luminance of 2300 cd/A and a current density of 640 mA/cm2 at 5 V.
Keywords: MEH-PPV; Electroluminescence; Polymer blend;

Triindolylmethane-based high triplet energy glass-forming electroactive molecular materials by Mindaugas Kirkus; Ramunas Lygaitis; Ming-Han Tsai; Juozas V. Grazulevicius; Chung-Chih Wu (226-232).
A series of new triindolylmethane-based compounds including those containing reactive functional groups were synthesized by the tandem addition–elimination–(Michael) addition reaction from 1H-indole and 1H-indole-3-carbaldehyde. The thermal, optical, photophysical and photoelectrical properties of the synthesized compounds were studied. The synthesized compounds exhibit moderate thermal stability with 5% weight loss temperatures ranging from 245 to 310 °C and form glasses with glass transition temperatures in the range of 98–123 °C. The ionization potentials of the synthesized compounds measured by the electron photoemission in air technique range from 5.67 to 5.80 eV. The solutions of the synthesized compounds show relatively high triplet energies in the range from 2.97 to 2.99 eV.
Keywords: Triindolylmethane; Molecular glass; High triplet energy; Ionization potential;

A method was developed for the determination of the protonation constants ( K H n L n H , L ), the stoichiometric factor of the protonation reaction (n) and pH of the half-color transition point (pH1/2) of three different types of electrochemically polymerized poly(aniline) (PANI) and poly(o-methylaniline) (PoMeANI) films. The protonation constants describe the reversible emeraldine base (EB) to emeraldine salt (ES) transition. The calculations of the constants were based on absorbance data obtained from UV–vis measurements of the polymer films equilibrated in pH buffer solutions between pH 2 and 12.It is shown that the protonation constant of the PANI film depends on the size of the acid counter ion, which is incorporated in the polymer film during electropolymerization in aqueous solution. Protonation constants of log K H n L n H , L = 3.5 (n  = 0.57) and 5.4 (n  = 0.56) were calculated for the PANI films prepared from a monomer solution containing 1.0 M HCl [small Cl anion; PANI(Cl)] and 0.1 M DBSA [bulky DBS anion; PANI(DBS)], respectively. The UV–vis spectra and pH1/2 shows that the electrically conducting protonated ES form of the PANI(DBS) film has a high stability and stays in the electrically conducting ES form between pH 2 and 7. In contrast, the PANI(Cl) film is mainly in the non-conducting EB form already at pH 7. The PoMeANI(Cl) film has a protonation constant of log K H n L n H , L = 3.2 (n  = 0.61). It shows, in combination with pH1/2, that ring substitution lowers the stability of the ES form of PoMeANI(Cl) in comparison to the non-substituted PANI(Cl) film.
Keywords: Protonation constants; Average proton number; pH sensitivity; Poly(aniline); Poly(o-methylaniline); Emeraldine base; Emeraldine salt; UV–vis spectroscopy;

Aqueous zinc–polyaniline secondary battery by Shengqi Li; Guolin Zhang; Guolin Jing; Jinqing Kan (242-245).
An aqueous zinc–polyaniline secondary battery was constituted by the polyaniline synthesized in a mixed solution containing 0.60 mol dm−3 aniline, 1.20 mol dm−3 1-ethyl-3-methylimidazolium-ethyl sulfate (EMIES) and 2.0 mol dm−3 H2SO4, Zn foil and an electrolytic solution containing 2.0 mol dm−3 ZnCl2 and 3.0 mol dm−3 NH4Cl with pH 6.0. The capacity and energy densities of the polyaniline are 141.2 A h kg−1 and 169.4 W h kg−1 for discharge process at 0.5 mA cm−2, respectively, which are much better than those of the polyaniline synthesized in HCl at the same current densities. The battery was successively charged/discharged at constant current densities, the columbic efficiency was 95.5% at 150th cycle, and the energy density of the battery was lower by only 6.0% at 150th cycle than at 1st cycle.
Keywords: Electroactive polyaniline; 1-Ethyl-3-methylimidazolium-ethyl sulfate; Ionic liquid; Zn–polyaniline battery;

Spectral properties of the TCNQ anion radical salt (N-Me-2,5-(Me)2-Pz)(TCNQ)2 by B. Barszcz; A. Graja; D.V. Ziolkovskiy; V.A. Starodub (246-250).
We present the optical conductivity, infrared- and Raman-active charge sensitive phonon modes of the new 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) anion radical salt containing N-methyl-2,5-dimethyl-pirazinium cations (N-Me-2,5-(Me)2-Pz)+. Comparison of the calculated frequencies of the totally symmetric TCNQ modes with corresponding vibrations in the (N-Me-2,5-(Me)2-Pz)(TCNQ)2 salt is given. An attribution of the main bands observed in the spectra of the salt is offered and discussed. The charges estimation with both, structural and spectroscopic methods is in good agreement with each other and confirms almost full charge transfer from cation to TCNQ species.
Keywords: TCNQ anion radical salt; Pirazinium-derived cation; IR and Raman spectra; Optical conductivity;

As nanomaterial possessing moderate conductivity, magnetic and dielectric property, novel hexanoic acid (HA)-doped polyaniline (PAni) nanocomposites containing TiO2 nanoparticles (dielectric filler) and carbon nanotubes, CNTs (magnetic fillers such as single-walled carbon nanotube, SWNT and multi-walled carbon nanotube, MWNT) were prepared by template free method. The PAni were characterized by UV, FTIR, X-ray diffraction (XRD), thermogravimetric (TGA) and scanning electron microscopy (SEM) analyses. Conductivity, magnetization, dielectric and microwave absorption properties of PAni were also investigated. The resulted nanorods/tubes as shown in SEM images clearly show that polymerization is proceeded in micelle/water interface through elongation. During template free method, TiO2 and CNT exist in the center of Ani/HA micelle. The SEM images show that some of the CNT enwrapped with PAni layer indicate CNT are just packed underneath the PAni and never attacked by PAni. PAni/HA/TiO2/SWNT with 20% of SWNT exhibits the best microwave absorption property (∼99.2% absorption) with reflection loss of −21.7 dB at 6 GHz due to its moderate conductivity (1.27 S/cm), magnetization (M s  = 1.01 emu/g), highest tan  δ and heterogeneity.
Keywords: Polyaniline; Nanocomposites; TiO2; Carbon nanotube; Conductivity; Microwave absorption property;