A. V. Vannikov

Electroluminescence of polymer/J-aggregate composites

Efficient electroluminescence was revealed in single-layer light-emitting diodes based on electron-hole conducting polymers containing the nanocrystalline phase of cyanine dyes (J-aggregates). These species exhibit a very narrow emission band with a maximum in the red to infrared spectrum range. The J-aggregates play an active role in the charge carrier transport of the composites.

Near-infrared electroluminescence in polymer composites based on organic nanocrystals

IR electroluminescence was revealed in single-layer light-emitting diodes based on a type of electroactive polymer nanocomposites-electron-hole conducting aromatic polyimide and organic nanocrystalline particles of cyanine molecules, known as J-aggregates. These materials exhibit a very narrow emission band with a maximum at 815 nm. Dramatic increase of charge-carrier mobility was observed for these layers containing the J-aggregate nanocrystalline phase.

Solvent-induced supramolecular assemblies of crown-substituted ruthenium phthalocyaninate: morphology of assemblies and non-linear optical properties

The information concerning the architecture of supramolecular assemblies, which are composed of ruthenium(II) tetra-15-crown-5-phthalocyaninate with axially coordinated triethylenediamine molecules, has been obtained with the application of atomic force microscopy. The ensembles are formed in Ru(II) complex solutions in chloroform and tetrachloroethane. The number of molecules and their relative orientation in supramolecular assemblies were estimated in dependence of the solvent (chloroform, tetrachloroethane) and the heating temperature. Samples fabricated after heating of the Ru(II) complexes solution in tetrachloroethane formed stable supramolecular wires of 600 nm and more in length. The third-order non-linear optical characteristics of complexes in tetrachloroethane solution were studied by the z-scanning method. Molecular polarizability of the complex is about 4.5 × 10-32 esu. The polarizability attributed to one molecule increases by a factor of 3.6 when the individual molecule assembles into a supramolecular aggregate.

A comparative voltabsorptometric study of polyaniline films prepared by different methods

Abstract A comparative cyclic voltabsorptometric study was carried out for polyaniline (PAn) films prepared by electrochemical polymerization and vacuum thermal evaporation. The absorption values were measured at different characteristic wavelengths (895, 755, 665, 435, and 325 nm) corresponding to the individual absorption bands separated by us earlier from the spectra using the Alentsev–Fock method. Differential voltabsorptometric curves (dA/dt vs. potential (DCVA)) measured in aqueous HCl were compared with ordinary cyclic voltammetry (CVA). The experiments for different sweep rates were also compared. It was found that the DCVA peak at 895 nm corresponds perfectly to the CVA peak both in the electrosynthesized and the vacuum deposited PAn. The DCVA peak at 435 nm (cation-radicals) precedes the CVA peak (similar to the maximum of the EPR signal), while that at 755 nm (polarons or cation-radical dimers) lags behind the CVA peak. For the vacuum deposited films an intense intermediate DCVA and current peaks (at about 0.6 V vs. Ag/AgCl) are observed. The results are discussed in terms of the heterogeneous structure of PAn; particularly, its specific features in the films prepared using different methods.

Bright blue–green electroluminescence from aromatic polyimides

New polyimide type of polymers, aromatic polyimides (APIs) containing sulphur atoms in the backbone, were investigated as electron-hole transporting and light-emitting materials for use in unilayer electroluminescent diodes. The simplicity of synthesis, high thermal stability, organic solvent solubility together with excellent film-forming properties make the APIs potentially of interest for technological applications.

Photorefractive polymer composites for the ir region based on carbon nanotubes

The photorefractive properties of polymer composites based on aromatic polyimide and single-wall carbon nanotubes are studied using radiation at a wavelength of 1064 nm. It is found that the nanotubes possess photoelectric sensitivity in this spectral region and that the kinetic photorefractive characteristics of the polymer composites are entirely determined by the photogeneration and charge transport characteristics of the layers. The two-beam gain coefficient of the signal beam measured for a composite consisting of aromatic polyimide and 0.25 wt % of single-wall carbon nanotubes in a constant electric field E0 = 79 V/μm is equal to 84 cm−1 and exceeds the optical absorption coefficient by 59 cm−1. The refractive index modulation is equal to Δn = 0.004 at E0 = 54 V/μm.

Photoelectric, nonlinear optical and photorefractive properties of polyimide doped with J-aggregates of cyanine dye

Abstract Novel solid-state photorefractive compositions consisting of the aromatic polyimide ( T g is about 230 °C) and the thiacarbocyanine dyes were prepared. These systems have the high net gain coefficient, Γ − α , about 360 cm −1 . The dyes form the nanocrystalline J -aggregates that are responsible for photoelectric sensibility in the region of action of Ar–Kr laser and are known to have also very high third-order macroscopic polarizability. The Kerr electrooptical effect is mainly responsible for the light induced refractive index change. It is established that the charge photogeneration time constant determines the time of the photorefractive grating formation and depending on the dye used may be about 20 ms. So, it became possible to develop the solid-state high-performance photorefractive layers based on the polymer with high T g .

Electron drift mobility in pyrazolo[3,4-b]quinoline doped polystyrene layers

Pyrazolo[3,4-b]quinoline derivatives are found to have electron transport properties. A field dependent electron drift mobility, in the range of 10−6–3×10−5 cm2/(V s) at an electric field of (1–7)×105 V/cm, has been found from the pyrazolo[3,4-b]quinoline doped polystyrene specimen, which was measured using a conventional time-of-flight method. The results are fit well into a correlated disorder model for a dipole medium when energetic features of the transport molecules are also taken into account.

Aromatic Polyimides as Efficient Materials for Organic Electroluminescent Devices

Derivatives of newly synthesized aromatic polyimides containing sulphur atoms in the backbone were studied as electron-hole-transporting and light-emitting materials for use in combination with tris(8-hydroxyquinoline)-aluminium in multilayer organic electroluminescent devices. Efficient bipolar charge transport has been revealed in the polymers. Bright electroluminescence (15 000 cd m -2 at 14V) was observed in the visible range. The possible role of intermolecular donor-acceptor interactions in the mechanism of electroluminescence is discussed.

J-AGGREGATE ELECTROLUMINESCENCE IN DYE DOPED POLYMER LAYERS

The electroluminescence (EL) of a dye nanocrystalline phase was revealed in single layer light-emitting diodes based on polymers doped with cyanine dye molecules. Observation of light emission in the visible range depended on the redox potentials of the dyes used. The 9,10-dithioanthracene-containing polyimides exhibiting efficient electron-hole transport appeared to be appropriate media for the generation of J-aggregate EL.