E. I. Mal’tsev

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.

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.

Synthesis, structure, photo- and electroluminescence studies of bis[2-(N-tosylamino)benzylidene-4′-dimethylaminophenylaminato]zinc

A new bis[2-(N-tosylamino)benzylidene-4′-dimethylaminophenylaminato]zinc complex was synthesized, its structure was studied by methods of elemental analysis, IR spectroscopy, 1H NMR spectroscopy, X-ray absorption spectroscopy, and quantum chemical calculations. Electron absorption and photoluminescence spectra of the zinc complex were investigated. An OLED device based on it was made and found to emit “soft” yellow light with CIE coordinates (x = 0.431, y = 0.537) and radiation luminance 1300 cd m−2 at a working voltage of 14 V.

Electrophosphorescence of aromatic polyimides doped with platinum porphyrins

The mechanism of electroluminescence in polymeric thin-layer devices based on aromatic polyimides and various molecular complexes of Pt porphyrins as heavy-atom-containing luminophores was studied. On the basis of spectral and electron-hole transport properties of aromatic polyimides and Pt porphyrins, as well as the current concepts adopted in polymer photonics, the processes of singlet-singlet and triplet-triplet energy transfer in the examined single-layer systems aromatic PI-Pt porphyrin with a high electrophosphorescence quantum yield exceeding 2% are discussed.

Synthesis and photo- and electroluminescent properties of copolyfluorenes with nile red fragments in side chains

New copolyfluorenes containing units of 4,7-dibromo-2,1,3-benzothiadiazole (green luminophore) and 3,6- or 2,7-dibromocarbazole derivatives with side-chain fragments of green (4-pyrrolidinyl-1,8-naphthalimide) and red (Nile red) luminophores and additional carbazole or diphenyloxadiazole groups are synthesized via the Suzuki copolycondensation reaction. The structure of the polymers is modified via insertion of triphenylamine, aryloxadiazole, and quinoxaline units in the backbone of copolyfluorenes and via introduction of triphenylamine, fluorene, and benzene terminal groups. The molecular-weight characteristics of the polycondensation products and the specific features of the transfer of polyfluorene emission energy to the indicated luminophores in solutions and films are studied. Coating the emissive copolyfluorene layer with electron-conducting and hole-blocking layers of poly[9,9-bis(6′-diethoxyphosphorylhexyl)fluorene] makes it possible to increase the brightness of light-emitting diodes (to 2380–3900 cd/m2) and their current and luminance efficiencies.

High precision nanoscale AFM height measurements of J-aggregates

Atomic force microscopy (AFM) was used to obtain high-resolution images of nanosized organic J-aggregate molecular crystals of 3,3′-di(gamma-sulfopropyl)-5,5-dichlorotiamonomethinecyanine (TC) and 3,3′-bis(2-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) and precise height measurements of J-aggregates monolayers were conducted. It was found that TC J-aggregates obtained both in the solution bulk and by self-assembly on the mica surface are extended monolayer sheets of high mechanical flexibility. The height of TC is 1.05 ± 0.05 nm, which corresponds to the crystallographic size of a single molecule along the short axis. A model of asymmetric single-layer molecular packing is suggested in which sulfopropyl groups are located on the same side of the layer plane. In the case of C8S3, narrow multilayer ribbonlike structures with heights of 3 to 30 nm were observed. The heights are strictly quantized with a step of 3 nm. A bilayer model of C8S3 molecular packing in J-aggregates is discussed with partially interpenetrating monolayers with hydrophobic sides oriented face to face. A model of structural C8S3 units as “elementary ribbons” with the transverse dimensions of 3 × 4 nm is suggested on the basis of the comparison of AFM data with electron microscopy data from other works.

Synthesis, Crystal Structure, and Electroluminescent Properties of Zinc and Cadmium Tetradentate Azomethine Complexes

Chemical and electrochemical syntheses of zinc(II) and cadmium(II) complexes based on tetradentate Schiff bases (H2L1 and H2L2) resulting from condensation of 2-tosylaminobenzaldehyde with 3,6-dioxa-1,8-octanediamine or 4,9-dioxa-1,12-dodecanediamine were performed. The structure, composition, and properties of the complexes were studied by elemental analysis, IR, 1H NMR, and UV spectroscopy, X-ray absorption spectroscopy, and X-ray diffraction. The zinc(II) and cadmium(II) complexes luminesce in a DMF solution in the blue spectral region (λPL = 425–433 nm), the photoluminescence quantum yield φ being 0.25–0.30. Multilayer zinc(II)- and cadmium(II)-based electroluminescent structures with green-blue emission of the exciplex nature were fabricated.

Synthesis, structure, and spectral studies of zinc and cadmium complexes with 2-tosylaminobenzaldehyde and aminoquinoline azomethine derivatives

New zinc and cadmium complexes with 3-[2-(N-tosylaminobenzylidene)]aminoquinoline (HL1) and 6-[2-(N-tosylaminobenzylidene)]aminoquinoline (HL2) were synthesized. The structures of HL1, HL2 and complexes ML2 (M = Zn, Cd) were established based on the elemental analysis data, IR spectroscopy, 1H NMR spectroscopy, and quantum chemical calculations. Electron absorption and photoluminescence spectra of the complexes were studied. OLED devices were developed, where ZnL22 complexes were used as an emission layer. This device emitted yellow light with CIE x = 0.436, y = 0.492 and x = 0.463, y = 0.484, maximum luminance at 10 V was 126 and 150 cd m−2, respectively.

Tubular structure of J-aggregates of cyanine dye

1 A heightened interest in certain supramolecular organic structures is associated with their unusual optical and electronic properties. These structures include J aggregates of cyanine dyes that represent a variation of micro and nanosized molecular crystals with strong and narrow absorption band (J band) in the visible range shifted toward longer wavelengths as compared with the spectrum of monomers [1, 2]. Owing to high electron–hole conductivity and special spectral properties caused by excitation of delocalized Frenkel excitons, J aggregates are promising organic systems for application in different optoelectronic devices [3–7].

Bis[2-(4′-Bromopyrazolyl-1′)-3-Tosylaminopyridinato]zinc(II): Synthesis, structure, and luminescence properties

Abstract2-(4′-Bromopyrazolyl-1′)-3-tosylaminopyridine (HL3) and its complex ZnL2 (I) are synthesized, and their structures are studied by IR, UV, and 1H NMR spectroscopy. The molecular structure of complex ZnL2 is determined by X-ray diffraction analysis. The atomic structure of ZnL2 is confirmed by the optimization of the molecular geometry using quantum-chemical calculations in the density functional theory approximation. The experimental bands in the absorption spectrum of complex I are interpreted on the basis of the calculations, and its photoluminescence properties are studied.