Properties and the nature of electric-field-induced variations in optical absorption spectra of polymethine dyes in polymer matrices

The effect of a permanent electric field on the absorption spectra of ionic (cationic and anionic) and intraionic symmetric and asymmetric polymethine dyes in poly-N-epoxypropylcarbazole, polyvinylbutyral, and polystyrene polymer films is studied. It is found that the electric field causes an increase in absorption of symmetric dyes in the short-wavelength region and a decrease in their absorption in the long-wavelength region. Asymmetric dyes exhibit opposite properties. These properties are common for these groups of dyes irrespective of their chemical structure and ionic nature. They are retained both in photoconducting polymers and in polymers that are incapable of charge photogeneration. These effects also take place in liquid solutions, although in this case they are much weaker. Various mechanisms of the influence of an electric field on the spectra, such as the electron transfer, Stark and Kerr effects, intermolecular interactions, and dye isomerization, are discussed. It is shown that the spectral effects are caused by the redistribution of the electron density in a chromophore of the dye in the ground state resulting in a change in the probability of vibronic transitions.     

High frequency impedance of cobalt-based soft magnetic amorphous ribbons near the Curie temperature

The impact of FeNi magnetic conductive coating on the high frequency impedance of Co₆₄Fe₃Cr₃Si₁₅B₁₅ amorphous ribbons and its dependence on an external magnetic field’s strength and temperature is studied. It is shown that the coating affects the range of the magnetic field with the greatest change in the impedance of the external magnetic field, along with the temperature sensitivity of the impedance modulus and its components in the region of phase transition. The considerable differences between the properties of amorphous ribbons and CoFeCrSiB/FeNi composites found in this work allow us to evaluate the prospect of future studies aimed at developing magnetoimpedance elements for nonmarker biodetection.     

Synthesis,spectral properties,and solvatochromism of merocyanine dyes based on bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate

Di-, tetra-, and hexamethine merocyanines containing heterocyclic fragments with different electron-donor abilities have been synthesized on the basis of bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate. Their electronic absorption spectra in solvents with different polarities have been studied, and their electronic structure and electronic transitions have been analyzed by DFT and TDDFT quantum chemical calculations using B3LYP functional and 6-31G(d,p) basis set. The electronic structure of the synthesized merocyanines changes from neutral polyene to polymethine and dipolar polyene, depending on the electron-donor ability of the heterocyclic fragment, length of the polymethine chain, and solvent polarity. Therefore, these merocyanines display positive, negative, and reverse solvatochromism.     

Phase transitions in a MgB<Subscript>2</Subscript> granular BCS superconductor in weak magnetic fields

The character of temperature dependences of the electric conductivity of MgB₂ granular BCS superconductors at temperatures of ~35–45 K in external magnetic fields H _ext of up to ~2 kOe is studied. An increase in the superconducting transition width ΔT _c with an increase in Hext is found. The presence of a system of weak links in MgB₂-based granular superconductors is established. On the basis of experimental data, MgB₂ granular superconductor is assigned to two-level superconducting systems and the H–T phase diagram is constructed.     

The dynamics of phase changes in a heat storage of thermal control system for onboard radio-electronic equipment

The paper considers a heat storage (HS) based on the materials with a “solid-liquid” phase change for a thermal control system for on-board radio electronic equipment (REE) with periodic and short time action. To intensify the heat transfer in the HS design, ribs made of hyper heat-conducting plates are used. The dynamics of temperature fields and phase transformations in the HS volume is studied on the basis of numerical modeling. The results of calculations have shown that the use of ribs in the form of hyper heat-conducting plates allows significantly reducing the amplitude of temperature fluctuations at the seat of the REE unit.     

Photogeneration of holes and electrons in amorphous molecular semiconductors with neutral and ionic organic dyes

Photoconducting properties of amorphous molecular semiconductors based on polystyrene films doped with tetranitrofluorenone and merocyanine or an anionic polymethine dye, or with epoxypropylcarbazole and merocyanine or a cationic polymethine dye were studied. The former type of the films is characterized by electron conductivity, whereas the latter type by hole conductivity. The activation energy for photogeneration of mobile charge carriers increases on passing from a merocyanine dye to ionic dyes and decreases with a growth in quantum energy of excitation light for the films of the former type, but does not depend on the light quantum energy for the films of the latter type. It was concluded that the activation energy of photogeneration is determined by electrostatic interaction of a photogenerated charge carrier with the ionized photogeneration site or a counterion for neutral and ionic dyes, respectively. At low dissipation rates of the excess thermal energy of excited dye molecules via electron-nucleus interaction, photogenerated electrons have a possibility to travel over a long distance from the photogeneration site as compared with holes.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 3, 2005, pp. 195–203.Original Russian Text Copyright © 2005 by Davidenko, Derevyanko, Zabolotnyi, Ishchenko, Kuvshinskii, Studzinskii.     

Pyrylocyanines. 23. 2-Pyrylocarbocyanines with substituents in hetero residues

Symmetric 2-pyrylo- and asymmetric (indo)(2-pyrylo)trimethinecyanines with substituents of different electronic nature in the pyran residue were synthesized. The influence of the conjugation effect and inductive effect on the characteristics of absorption bands of the synthesized dyes was analyzed by a quantum chemical calculation according to a common MO Hückel method.For Communication 22, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii No. 12, pp. 1607–1613, December, 1986.     

Pyrylocyanines. 15. Benzopyrylo-2-cyanines

Symmetrical 4,4-diphenyl-substituted benzopyrylo-2-monomethylidyne, carbo-, and dicarbocyanines and their thio analogs, as well as unsymmetrical carbocyanines that contain, in addition to 4-phenylbenzopyrylium or 4-phenylbenzothiopyrylium rings, 3-ethylbenzothiazolium or 1,3,3-trimethyl-3H-indolium residues, were synthesized. The indicated dyes were more highly colored than their isomers that contain flavylium or thioflavylium residues. On the basis of the deviations calculated from the centers of the absorption bands it was concluded that the benzopyran residues in the dyes of the series have greater electron donor character than those in the dyes of the series.See [1] for communication 14.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1173–1177, September, 1982.