Photoinduced hole dipoles' mechanism of liquid crystal photoalignment.

Polarized light absorption in photoalignment material induces anisotropic long-range interactions that orient liquid crystals. The main physical mechanisms behind anisotropic interactions are photocrosslinking and photodestruction of polymers, and photoisomerization and photorotation of azo dyes. Investigation of AtA-2 azo dye azimuthal anchoring versus exposure dose revealed the presence of an unusually strong anchoring peak at low doses, which is beyond our understanding of the known mechanisms. Here we explain these observations and demonstrate the existence of a photoalignment mechanism based on photoinduced hole dipole moments in the azo dye layer. Strong azimuthal anchoring energy >2×10-4J/m2 is obtained with a <0.5J/cm2 exposure dose.

Electric Field Oriented Nanostructured Organic Thin Films with Polarized Luminescence.

The effect of the external electric field of 105 V/m on the ordering of two luminescent liquid crystalline molecules (1-pentyl-2/,3/-difluoro-3///-methyl-4////-octyl-p-quinguephenyl and 9,10-Bis (4-pentylphenylethynyl)antracene) during thermal vacuum deposition is studied. The morphology, electrical conductivity, optical absorption, luminescence spectra, and polarization are presented and analyzed. All data show the formation of ordered films. The polarization degree is 60% for 1-pentyl-2/,3/-difluoro-3///-methyl-4////-octyl-p-quinguephenyl oriented films and 28% for 9,10-Bis (4-pentylphenylethynyl)antracene. The lower value of M2 luminescence polarization can be explained by the absence of dipole moment in this molecule.

Experimental and theoretical study of photo- and electroluminescence of divinyldiphenyl and divinylphenanthrene derivatives.

Electronic absorption and luminescence spectra of four new compounds of divinyldiphenyl and divinylphenanthrene derivatives are investigated experimentally in tetrahydrofuran solutions and thin films obtained by thermal vacuum deposition and by spin coating of these substances embedded into polyvinylcarbazole matrix. Molecular geometry optimizations and electronic spectra have been calculated in the framework of XMC-QDPT2/6-31G (d, p) and TDDFT/B3LYP/6-31G (d, p) levels of theory. We have fabricated and studied OLED devices with the structure ITO/PEDOT:PSS/NPD/L/Ca/Al and ITO/PEDOT:PSS/PVK+L/Ca, where L is the luminophore. It is demonstrated that the photo-and electroluminescence spectra of divinyldiphenyl are not identical and undergo strong changes depending on the method of sample preparation.

Ionization of 4,4'-bis(phenylethynyl) anthracene by electron impact.

Ionization of a 4,4'-bis(phenylethynyl)anthracene (C(30)H(18), BPEA) molecule is studied for the first time at different energies of bombarding electrons in crossed electron and molecular beams. The relative cross-section of single ionization of a BPEA molecule in the energy range of 5-55 eV is measured. The ionization potential, E(I) = 7.62 +/- 0.2 eV, is determined using the threshold region of C(30)H(18)(+) ion yield energy dependence. A scheme of the BPEA molecule fragmentation is proposed. Experimental results are in reasonable accordance with calculations made in the framework of the density functional theory.

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.

Interaction of low-energy electrons with linear diphenylethynyl derivatives in the gas phase.

The gas phase electron impact spectroscopy has been used to study the relative efficiency of excitation into singlet states and energies of singlet-triplet transitions for two electroactive organic materials, anthracene and biphenyl-containing diphenylethynyl derivatives. The probability of the lowest singlet-triplet transition in anthracene-containing molecule was found to be much higher than that in anthracene which is connected with triple bonds. No noticeable contribution of the triple bonds into singlet spectra of the studied molecules was observed. There are a number of intense transitions in the range higher than 10 eV. The optical spectrum calculated using the density functional theory is in good agreement with experimental electron energy loss and optical absorption spectra.

[Gamma-aminobutyric acid content and activity of the enzyme synthesizing it in blood plasma of children exposed to ionizing radiation as a result of the accident at the Chernobyl nuclear power plant]. / Soderzhanie gammaaminomaslianoi kisloty i aktivnost' fermenta ee sinteza v plazme krovi detei, podvergavshikhsia vozdeistviiu ioniziruiushchei radiatsii vsledstvie avarii na Chernobyl'skoi AES.

Marked individual fluctuations in blood levels of GABA and GDC revealed in 35 to 50% of adolescents exposed to ionizing radiation several years before indicate the presence of an imbalance in the GABA-ergic system. These children (with GABA-ergic system disturbances) represent a group at risk of developing remote effects of radiation exposure presenting as disturbed rhythms and terms of sexual maturation, of growth, thyroid and adrenal abnormalities, and they should be regularly checked up.