Eduard E. Kolesnik

Spectral and Luminescent Properties and Electroluminescence of Polyvinylcarbazole with 1,8-Naphthalimide in the Side Chain

A novel copolymer with moieties capable of charge transport and light emission on the basis of polyvinylcarbazole and 1,8-naphthalimide is synthesized. A bright and stable electroluminescence from single layered structure is observed. White light emission can be easily realized by tuning the content of naphthalimide moieties or a number of naphthalimide derivatives. Such approach can be considered as a common way to create single layered light-emitting devices with a stable white emission.

Spectroscopic and Morphological Properties of Divinylbenzoxazolylbiphenyl Thin Films

The thin organic films based on 4,4′-bis-[(Z)-1-(1,3-benzoxazol-2-yl-2-ethenyl)]biphenyl and its partly fluorinated derivatives are studied. Absorption, luminescence, and excitation spectra, luminescence decay and film morphology were found to depend sensitively on the changes in molecule structure, nature and temperature of the substrate, as well as the thermovacuum deposition rate, being the origins of bad reproducibility of the optical properties of such films. Molecular aggregation with chromophore dipoles arranged parallel to each other has been observed in absorption and luminescence spectra. The fluorescence characteristics can be explained by the combination of radiation of aggregated and non-aggregated molecules. The main characteristics of the molecules under study are calculated using DFT approach. The unusual behaviour of photodegradation in fluorinated film is found.

Electrical and luminescence properties of a poly(amidoamine) dendrimer containing naphthalimide

The electrical and luminescence properties of a poly(amidoamine) (PAMAM) dendrimer containing naphthalimide are investigated. The influence of adsorbed oxygen on the electrical conductivity of thermally evaporated organic films is analyzed using cyclic thermal desorption. The results obtained are interpreted within a model of two-level hopping electron transfer according to which one of the two systems of energy levels corresponds to intrinsic states of electrons in PAMAM molecules and the other system is associated with the states of electrons in adsorbed oxygen molecules. The use of the cyclic thermal desorption method in combination with the proposed model makes it possible to estimate the localization length of electrons numerically and to determine the states involved in hopping electron transfer. It is demonstrated that the studied compound in the solid state possesses a high luminescence power over a wide spectral range.

Effect of Temperature and Oxygen on Luminescence Spectra and Polarization of Divinylbenzoxazolylbiphenyl Thin Films

H-type molecular aggregation as assembly with chromophore dipoles arranged parallel to each other has been observed in absorption and luminescence spectra of divinylbenzoxazolylbiphenyl thin films deposited on quartz glass substrate by thermovacuum method. The reversible changes of fluorescence anisotropy have been observed under film heating below the glass transition temperature correlating with lifetime changes. The addition of oxygen was found to cause an essential luminescence quenching. The hexyloxy group in the side chain of dibenzoxazolylbiphenyl molecule decreases H-type molecular aggregation and energy migration, and increases luminescence quenching induced by adsorbed oxygen owing to the formation of more porous film morphology.

Porous alumina-based cathode for organic light-emitting devices

We propose a new cathode for organic light-emitting devices based on anodic porous alumina films. For this purpose usual and modified porous alumina and structured aluminum with removed porous alumina layer can be used. The usage of porous alumina cathode results in more inhomogeneous electric field and, as a consequence, more intensive auto electron emission and cathode efficiency. Owing to extended surface this matrix also gives the possibility to reach higher luminophor concentration without noticeable luminescence quenching. Organic electroluminescent devices of this type are easily produced and can be more efficient and stable as compared with usual layered structures. An intensive secondary electron emission is observed after irradiating of activated alumina matrix by an electron beam. We developed one of the proposed porous alumina cathode based organic electroluminescence structure doped with amorphous naphthalimide derivative. A bright electroluminescence of naphthalimide in such a structure was observed for the first time. The ways of the further development of this structure are pointed out.

Organic‐Inorganic Nanocomposites: Optical and Electrophysical Properties

A short review on achievements of conducting and luminescent nanocomposites as well as spectroscopic and electrophysical properties of thin polymer films containing metal and semiconductor nanoparticles and the data of studies of thin films and ITO/nanocomposite/Al or metal/nanocomposite/metal structures mainly based on poly‐N‐epoxypropylcarbazole (PEPK) with Ag or Ag/Au and CdS nanoparticles are presented. It is shown that these nanocomposites are very promising materials for creation of printed electronics circuitry and scintillation screen of field emission displays.

Spectral‐Luminescence Characteristics of Polyphenyls and Polyacenes in the Gas Phase in Electron‐Beam Excitation

The spectra of electron‐energy loss, excitation functions, and fluorescence spectra in excitation of the vapor of polyphenyls and polyacenes by electron beams of different energies are determined. The influence of successive complication of the molecules under study on these spectral‐luminescence characteristics is tracked. Unlike the optical absorption spectra, in the spectra of electron‐energy loss of all the substances studied one observes a band which is related to the singlet‐triplet transition S0–T1. The transitions up to S0–S5 are recorded in excitation of the molecules by high‐energy electrons, including the region of vacuum ultraviolet. From the functions of fluorescence excitation the authors have determined the excitation thresholds that correlate with the energies of the S1 levels, except for pyrene in which the S0–S1 transition is forbidden and does not show up not only in photon excitation but also in electron‐beam excitation, although the intercombination forbiddenness in the latter case is removed and the S0–T1 band is observed.

Spectral and electroluminescent properties of divinylbiphenylyl

The results of studies of the spectral, luminescent, and electroluminescent characteristics of four linear divinylbiphenylyl derivatives are presented. All the compounds under study fluoresce effectively in solutions and thin films in the blue spectral range. For thermally vacuum-deposited films, it is possible that absorption and luminescence spectra change due to aggregate formation. The studied biphenyl derivatives can electroluminesce in simple single-layer devices with a low (4 V) threshold voltage.

Transformation of energy in some laser dyes under excitation by electrons

The main characteristics of interaction of monokinetic electrons with different energies in the range from 0 to 50 eV at an angle 90 degree(s) (electron energy loss spectra, luminescence excitation functions, and luminescence spectra) for some lasing potential organic materials (paraquaterphenyl, 1,4-bis[2-(5- phenyloxazolyl)]benzene (POPOP), 2,5-biphenyloxazole (PPO), perylene, (beta) -binaphthilenoxide (dinaphthofuran), and 4-methylamino-N-(o-tolyl)-1,8-naphthalimide) are presented and analyzed. It was shown the correlation between elastic and inelastic scattering. It was found that the nature of electron and photon excitations is similar. Direct population of triplet states for most of studied compounds is negligible. The substances with intensive longwave singlet band (perylene, POPOP, PPO, naphthalimide) are very attractive for lasing search in electroluminescent cell. Calculation of excitation rates based on Born approximation results in essential error.

Modeling of Electroluminescence of Thin Organic Films

We propose a simple model for describing the electroluminescence in a single-layer thin-film organic electroluminescent cell on the assumption that the luminophore molecules are directly excited by electron impact and are the result of recombination. The calculated luminescence and efficiency curves are in qualitative and quantitative agreement with experimental data. To attain a high efficiency, it is necessary to use cathodes with a low work function and a high Fermi energy and relatively small electric fields.