Synthetic Metals (v.158, #11)

An A2  + B4 approach was adopted to synthesize a partially conjugated hyperbranched polymer HPBPV in which rigid fluorescent conjugated segments and flexible non-conjugated spacers arranged alternately through ether bonds in the skeleton. FT-IR, NMR and elemental analysis were employed to identify the structure of the monomers and polymer. The optimized conformation of HPBPV (one generation) demonstrated three-dimensional structure instead of two-dimensional structure of the fully conjugated hyperbranched polymer. Property investigations revealed that the polymer had good solubility in common organic solvents, good thermal stability and high glass transition temperature. It is also found that the end groups have an obvious impact on the solubility and thermal properties of the polymers, which was discussed in detail in the paper. The relative PL quantum efficiency of the polymer in dilute chloroform solution amounts to 62%. A brief LED device was fabricated and its electroluminescent performance was studied.
Keywords: Hyperbranched polymer; Luminescence; End group; Light-emitting;

Complexes of the type [PhHg]2[M(cdc)2], [Me2Sn][M(cdc)2], [n-Bu2Sn][M(cdc)2], [n-Bu3Sn]2[M(cdc)2] and [Ph3Sn]2[M(cdc)2] (M = Ni(II) and Cu(II); cdc2−  = cyanodithioimidocarbonate) and their I2-doped products have been prepared and characterized by microanalysis, magnetic and solution as well as solid phase conductivity measurements, IR, Raman, electronic, 1H and 13C NMR and ESR spectroscopic techniques. ESR silent diamagnetic compounds [PhHg]2[Cu(cdc)2], [Me2Sn][Cu(cdc)2], [n-Bu2Sn][Cu(cdc)2], [n-Bu3Sn]2[Cu(cdc)2] and [Ph3Sn]2[Cu(cdc)2] are strongly antiferromagnetically coupled. [PhHg]2[Ni(cdc)2] is weakly paramagnetic because of the weak axial interactions of sulfur atoms of the ligand cdc2− with some of the Ni(II) centers. Sharp 1H NMR signals suggest that [PhHg]2[Cu(cdc)2], [n-Bu2Sn][Cu(cdc)2], [n-Bu3Sn]2[Cu(cdc)2] and [Ph3Sn]2[Cu(cdc)2] remained diamagnetic in solution as well. Majority of the complexes exhibited σ rt in the range of 10−11 to 10−10  S cm−1 while the I2-doped products show enhanced conductivity in the 10−10 to 10−6  S cm−1 range and exhibit semiconducting behaviour.
Keywords: Organoheterobimetallic dithio complexes; Semiconductors; 1H and 13C NMR; UV–vis; I2-doping;

A series of stable salts of the oxidized donors TTF, o-Me2TTF, TMTTF, and TTF(SCH2CH2CN)4 by Eric W. Reinheimer; Hanhua Zhao; Kim R. Dunbar (447-452).
Reactions of the organic donors tetrathiafulvalene (TTF), o-dimethyltetrathiafulvalene (o-Me2TTF), tetramethyltetrathiafulvalene (TMTTF), and tetrathiafulvalene tetrathiolate [TTF(SCH2CH2CN)4] with oxidizing agents of suitable potential resulted in the formation of stable salts in which the donors are present in their monocationic radical forms. The salts presented herein represent a series of reagents containing oxidized chalcofulvalene donors that can be used as starting materials for metathesis reactions with other cations. All of the salts were characterized by X-ray crystallography and UV–vis–NIR spectroscopy.
Keywords: Organic donors; Stable salts; Cations;

Effect of electrolyte solvent on the morphology of polypyrrole films: Application to the use of polypyrrole in pH sensors by Stéphanie Carquigny; Olivier Segut; Boris Lakard; F. Lallemand; Patrick Fievet (453-461).
Electrochemical and morphological characteristics of polypyrrole (PPy) films electro-deposited from three different electrolyte solutions (acetonitrile, water and acetonitrile + water) have been investigated using atomic force microscopy and scanning electron microscopy. Experimental parameters including the electrolyte and the deposition time were shown to affect the morphologies of polypyrrole films. After characterization of the polypyrrole film morphologies, these polymer films were successfully tested as sensitive layers in pH sensors since the pH sensor responses were fast, linear and sensitive to pH changes. More, these responses of the pH sensors were dependent on the experimental conditions of the electro-deposition (thickness and solvent).
Keywords: Polypyrrole; Electrochemical oxidation; Polymer-modified electrodes; Scanning electron microscopy; Atomic force microscopy; pH sensors;

Carbazole-containing enamines as charge transport materials for electrophotography by A. Matoliukstyte; E. Burbulis; J.V. Grazulevicius; V. Gaidelis; V. Jankauskas (462-467).
Synthesis and thermal, optical as well as photoelectrical properties of carbazole-based enamines are reported. The synthesized compounds were found to form glasses with the glass transition temperatures up to 104 °C as characterized by differential scanning calorimetry. Electron photoemission spectra of the synthesized enamines have been recorded and the ionization potentials have been established. The lowest value of ionization potential (5.22 eV) and the best charge transport properties were shown by di(2,2-diphenylvinyl)(9-ethyl-3-carbazolyl)amine. Room temperature hole-drift mobilities in its 50% solid solutions in bisphenol Z polycarbonate established by the xerographic time-of-flight technique were found to be 9 × 10−5  cm2  V−1  s−1 at electric field of 106  V cm−1.
Keywords: Enamine; Glass; Ionization potential; Charge transport; Drift mobility;

High mobility n-channel organic field-effect transistors based on soluble C60 and C70 fullerene derivatives by Paul H. Wöbkenberg; Donal D.C. Bradley; David Kronholm; Jan C. Hummelen; Dago M. de Leeuw; Michael Cölle; Thomas D. Anthopoulos (468-472).
We report on n-channel organic field-effect transistors (OFETs) based on the solution processable methanofullerenes [6,6]-phenyl-C61-butyric acid ester ([60]PCBM) and [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM). Despite the fact that both derivatives form glassy films when processed from solution, their electron mobilities are high and on the order of 0.21 cm2/V s and 0.1 cm2/V s, for [60]PCBM and [70]PCBM, respectively. Although the derived mobility of [60]PCBM is comparable to the best values reported in the literature, the electron mobility of [70]PCBM is the highest value reported to date for any C70 based molecule. We note that this is the only report in which C60 and C70 methanofullerenes exhibit comparable electron mobilities. The present findings could have significant implications in the area of large-area organic electronics and organic photovoltaics where C60 derivatives have so far been the most widely used electron acceptor materials.
Keywords: Organic transistors; Methanofullerenes; Fullerene derivatives; n-Channel; Electron transport;

The thin-film field-effect-transistor model recently developed is applied to devices based on materials that already show current even without a bias present at the gate resulting in so-called normally-on transistors. These fall in three categories: (i) narrow-band-gap semiconductors, where the thermal energy is sufficient to excite carriers across the band-gap, here analyzed for unipolar and ambipolar materials, (ii) doped semiconductors, and (iii) metals. It is shown what the impact is on the IV and transfer curves.
Keywords: Thin-film field-effect transistors; Organic semiconductors; Two-dimensional electronics; Metal–insulator–metal transistor;