Pyrylocyanines. 11. Symmetrical tetraphenyl-substituted pyrylo-2-cyanines

Symmetrical polymethine dyes (monomethylidyne, carbo-, and dicarbocyanines), viz., 4,6-diphenylpyrylium, -thiopyrylium, and -pyridinium derivatives, were synthesized. It follows from a comparison of the absorption spectra of pyrylo-2-cyanines and their heteroanalogs with the spectra of the corresponding 4 isomers that these dyes differ from one another with respect to the positions, intensities, and forms of the bands. The pyrylocarbo- and -dicarbocyanines and their sulfur analogs are more deeply colored than their isomers, while the reverse regularity is observed in the pyridocyanine series. The long-wave bands in the spectra of all of the isomers are accompanied by more intensive transitions to the vibrational sublevels than in the case of the isomers.See [1] for Communication 10.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 898–902, July, 1980.     

Pyrylocyanines. 14. Unsymmetrical pyrylocyanines based on 2,3-polymethylene-4,6-diphenylpyrylium salts

Unsymmetrical 4,6-diphenylpyrylo-2-carbo- and dicarbocyanines, as well as the analogous pyridocyanines, containing 3-ethylbenzothiazolium and 1,3,3-trimethyl-3H-indolium residues and an ethylene or trimethylene bridging grouping between the position of the polymethine chain and the position of the pyrylium or pyridinium residue were synthesized. The introduction of bridging groups is generally accompanied by a bathochromic effect and intensification (in the pyrylocyanine series) or weakening (in the pyridocyanine series) of the fine structure of the absorption bands. On the basis of the deviations calculated from the centers of the absorption bands and the dependences of the vinylene shifts and the absorption band widths on the structure of the dyes it was concluded that the trimethylene bridging groups in the examined cases increase the electron-donor character of the heterocyclic residues in the dyes more markedly than the ethylene bridging groups.See [1] for Communication 13.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1327–1331, October, 1981.     

Pyrylocyanines. 30. Unsymmetrical 4,6,4′,6′-tetraphenyl-substituted 2-pyrido-2-pyrylocyanines with trimethylene groupings in the chromophore

The reaction of methylamine with symmetrical 4,6,4,6-tetraphenyl-substituted 2-pyrylopolycarbocyanines, in which both a positions of the polymethine chain are linked to the positions of the heterocyclic residues by trimethylene groups, was used to synthesize the corresponding pyridopyrylocyanines. The effect of trimethylene groupings in the 2-pyridocyanines on this transformation was examined. The principles involved in the color of the synthesized pyridopyrylocyanines were studied.See [1] for Communication 29.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 345–348, March, 1992.     

Synthesis and spectral properties of merocyanine dyes based on fluorene and its derivatives

The di-, tetra- and hexamethine merocyaninyes, the derivatives of fluorene, diphenyl 9H-fluorene-2,7-disulfonate, and bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9H-fluorene-2,7-disulfonate, as well as the derivatives of the heterocycles of moderate (indolylidene and benzotiazolylidene), weak (benzo[c,d]indolylidene and 2,6-diphenylpyrane) and strong (2,6-diphenylpyridine) electron-donor properties were synthesized and their absorption spectra in solvents of different polarity were studied. The quantum-chemical analysis of electronic structure of the synthesized merocyanines was performed and the types of electronic transitions in them were found by the DFT and TDDFT methods with the B3LYP/6-31G(d,p) basis.     

Non-Gaussian statistics of an optical soliton in the presence of amplified spontaneous emission

We apply an approach based on the Fokker-Planck equation to study the statistics of optical soliton parameters in the presence of additive noise. This rigorous method not only allows us to reproduce and justify the classical Gordon-Haus formula but also leads to new exact results.     

Information capacity of optical fiber channels with zero average dispersion

We study the statistics of optical data transmission in a noisy nonlinear fiber channel with a weak dispersion management and zero average dispersion. Applying analytical expressions for the output probability density functions both for a nonlinear channel and for a linear channel with additive and multiplicative noise we calculate in a closed form a lower bound estimate on the Shannon capacity for an arbitrary signal-to-noise ratio.     

A dye laser with a polyurethane matrix

A dye laser with a polyurethane matrix cured by polycondensation is studied. An increase in the conversion efficiency, service life, optical stability, and tuning range in comparison with lasing media produced by radical polymerization is demonstrated.     

Controlling soliton refraction in optical lattices

We show in the framework of the 1D nonlinear Schr?dinger equation that the value of the refraction angle of a fundamental soliton beam passing through an optical lattice can be controlled by adjusting either the shape of an individual waveguide or the relative positions of the waveguides. In the case of the shallow refractive index modulation, we develop a general approach for the calculation of the refraction angle change. The shape of a single waveguide crucially affects the refraction direction due to the appearance of a structural form factor in the expression for the density of emitted waves. For a lattice of scatterers, wave-soliton interference inside the lattice leads to the appearance of an additional geometric form factor. As a result, the soliton refraction is more pronounced for the disordered lattices than for the periodic ones.     

Radiation damages under irradiation of the BCS superconductor MgB<Subscript>2</Subscript> by high-energy electrons

This paper reports on the results of investigations of the influence of irradiation of the two-band BCS superconductor MgB₂ by electrons with an average energy $ \bar {\rm E} $ \bar {\rm E} ∼ 10 MeV at high doses (0 ≤ ϕt ≤ ∼2.5 × 10¹⁸ cm⁻²) on the temperature and width of the transition to the superconducting state, the temperature dependence of the electrical resistivity in the normal state, the crystal lattice parameters, and the diffraction line intensity. An increase in the electron irradiation dose ϕt leads to the following effects: a decrease in the critical temperature T _c ; an increase in the width of the superconducting transition ΔT _c ; and a decrease in the “residual electrical resistivity” ρ_{273 K}/ρ_{40 K}, in the parameters a and c of the hexagonal crystal lattice, and in the ratio between the diffraction line intensities I ₁₁₀/I ₁₀₀. From analyzing the results obtained, it has been established that the main type of radiation damages under irradiation of the BCS superconductor MgB₂ by high-energy electrons is the formation of vacancies in the B sublattice, which leads to a narrowing of the large band gap Δ_σ on the Fermi surface.