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Knyukshto V.N.,B. I. Stepanov Institute of Physics | Volkovich D.I.,B. I. Stepanov Institute of Physics | Gladkov L.L.,Higher State College of Communications | Kuzmitsky V.A.,Institute for Command Engineers | And 4 more authors.
Optics and Spectroscopy (English translation of Optika i Spektroskopiya)

We have performed complex experimental and theoretical investigations of the spectral-luminescent properties and electronic structure of new phthalocyanine analogs, Mg octaphenylporphyrazine and its derivatives with an annulated thiadiazole or selenadiazole ring instead of two phenyl groups. Fluorescence characteristics have been determined at 293 and 77 K: emission, excitation, and fluorescence polarization spectra; fluorescence quantum yield φF, and lifetime τF. Annulation of a five-membered chalcogen-containing heterocycle leads to splitting of the long-wavelength absorption band Q(0-0) and to the bathochromic shift of its longest wavelength component Qx(0-0), which increase upon passage from S to Se. At the same time, the fluorescence quantum yield φF and lifetime τF decrease, which is related to the intramolecular heavy-atom effect. The geometric structure of the ground state of the Mg porphyrazine molecules has been determined based on the density functional theory (DFT), and excited electronic states have been calculated with modified parametrization of the INDO/S method, INDO/Sm. Semiquantitatively, the calculated level positions of the lowest Q states and spectral shifts of Mg octaphenylporphyrazine and S-derivative agree with experimental data. For the range of the Soret band, calculated transition energies and their intensity distributions substantially depend on the dihedral angle γ between a phenyl ring and porphyrazine macrocycle. We show that, based on calculations at the angle γ = 60°, bands in the observed absorption spectra can be assigned with an accuracy of ~2000 cm-1. © Pleiades Publishing, Ltd., 2012. Source

Stsiapura V.I.,Kupala State University | Kurhuzenkau S.A.,Kupala State University | Kuzmitsky V.A.,Institute for Command Engineers | Bouganov O.V.,National Academy of Sciences of Belarus | Tikhomirov S.A.,National Academy of Sciences of Belarus
Journal of Physical Chemistry A

It has been established earlier that fluorescence quantum yield of thioflavin T (ThT) - a probe widely used for amyloid fibrils detection - is viscosity-dependent, and photophysical properties of ThT can be well-described by the fluorescent molecular rotor model, which associates twisted internal charge transfer (TICT) reaction with the main nonradiative decay process in the excited state of the dye. Solutions of ThT in a range of polar solvents were studied using steady-state fluorescence and sub-picosecond transient absorption spectroscopy methods, and we showed that solvent effect on nonradiative transition rate knr cannot be reduced to the dependence on viscosity only and that ∼3 times change of knr can be observed for ThT in aprotic solvents and water, which correlates with solvent polarity. Different behavior was observed in alcohol solutions, particularly in longer n-alcohols, where TICT rate was mainly determined by rotational diffusion of ThT fragments. Quantum-chemical calculations of S0 → S1 transition energy were performed to get insight of polar solvent contribution to the excited-state energy stabilization. Effect of polar solvent on electronic energy levels of ThT was simulated by applying homogeneous electric field according to the Onsager cavity model. Static solvent effect on the excited-state potential energy surface, where charge transfer reaction takes place, was not essential to account for experimentally observed TICT rate differences in water and aprotic solvents. From the other side, nonradiative decay rate of ThT in water, ethylene glycol, and aprotic solvents was found to follow dynamics of polar solvation knr ∼ τS -1, which can explain dependence of the TICT rate on both polarity and viscosity of the solvents. © 2016 American Chemical Society. Source

Goncharenko I.,Institute for Command Engineers | Marciniak M.,National Institute of Telecommunications
International Conference on Transparent Optical Networks

In paper the optical sensor allowing measuring both a direction and bend and stress values in building structures is described. The sensitive element of the sensor is the microstructured fiber with three cores. Distribution of mode fields in fiber cores depending on fiber structure and bend value is analyzed. The optimization of the sensitive element parameters depending on the purpose of use is proposed. © 2011 IEEE. Source

Pershukevich P.P.,National Academy of Sciences of Belarus | Volkovich D.I.,National Academy of Sciences of Belarus | Gladkov L.L.,Higher State College of Communications | Dudkin S.V.,Organic Intermediates and Dyes Institute | And 4 more authors.
Optics and Spectroscopy (English translation of Optika i Spektroskopiya)

The effect of the addition of phenyl groups to pyrrole rings of tetraazachlorins, a new class of tetrapyrroles, on the photophysical properties and electronic structure of the molecules has been investigated by a complex of experimental and theoretical methods. Characteristics of fluorescence at 293 and 77 K have been determined for phenyl-substituted tetraazachlorins. The objects of this study include unsubstituted tetraazaporphine. The introduction of phenyl groups affords a marked increase in the fluorescence quantum yield. For tetraazaporphine and phenyl-substituted tetraazachlorins, fluorescence buildup occurs as the temperature is decreased from 293 to 77 K, but to a lesser extent than for tetraazachlorins having no phenyl groups, which were earlier studied by the authors. The fluorescence buildup mechanism is discussed. The singlet oxygen generation quantum yield has been determined for the tetrapyrroles examined. This characteristic increases upon tetrapyrrole is phenylation. The electronic structure and absorption spectra of unsubstituted porphine and chlorin, tetraazaporphine, tetraazachlorin, octaphenyltetraazaporphine, and tetramethylhexaphenyltetraazachlorin have been calculated by the INDO/Sm method (original modification of the INDO/S method) with molecular geometry optimization using DFT. The results of the quantum-chemical calculation of the absorption spectra are in good agreement with experimental data for transitions to the lowest excited electronic states Qx(S1) and Qy(S2). © 2014, Pleiades Publishing, Ltd. Source

Kurochkin Y.,B. I. Stepanov Institute of Physics | Otchik V.,Institute for Command Engineers
Nonlinear Phenomena in Complex Systems

A possibility to define an analog of a uniform electric field in the Lobachevsky space is considered. Schrödinger equation for the hydrogen atom in this electric field is separated and Stark shifts of energy levels are evaluated. Source

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