Condensed heterocyclic compounds containing a thiazole ring. 12. Derivatives of thiazolo[3,4-b][1,2,4]triazine

Unsymmetrical monomethinecyanine dyes, containing a benzothiazole residue, were obtained from thiazolotriazine. To interpret the nature of the main absorption bands and localize the electronic transitions, the transition energies and electronic distribution of the first and second excited states of several model compounds were calculated by the self-consistent field method.For Communication 11, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1693–1697, December, 1986.     

Calculation of conformational equilibrium of biscarbocyanines from their absorption spectra

On the basis of the general characteristics of the interaction of two chromophores bound to the same molecule, we propose a method for calculating the conformer ratio from the absorption spectra of biscarbocyanines. The probability that the polymethine chain takes on a specific conformation may be calculated from the absorption spectral data of the investigated biscyanine, its analog with a fixed structure, and the result of construction of graphic models of the proposed conformers. All other conditions being equal, the factor deciding the conformational equilibrium is the effective volume of the atoms or the atomic groups in the 1 and 3 positions of the terminal heterocyclic nucleus. In the NH-biscyanine series, derivatives of the same azole, such a factor is the repulsion of like-charged chromophores (maximum in conformers with close chromophores and minimum in conformers with distant chromophores).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 426–435, July–August, 1986.     

Pyrylocyanines. 32. Free radicals of a series of tert-butyl-substituted pyrylocyanines and their heteroanalogs

The one-electron reduction of tetra-tert-butyl-substituted pyrylo- and thiapyrylocyanines of the - and -series was investigated by ESR spectroscopy and electrochemistry. The free radicals formed from cations of the indicated dyes were characterized.For Communication 32, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1638–1641, December, 1993.     

Condensed heterocycles with a thiazole ring. 15. Dyes based on thiazolo[3,4-b][1,2,4]triazine

Unsymmetrical tri- and pentamethinecyanine dyes with a thiazolo[3,4-b][1,2,4]triazine ring were synthesized. The electron-density distribution on the atoms of the dyes in the ground, first, and second excited states was calculated by a quantum-chemical method. It was established that the first two electron transitions are localized on the same atoms of the dyes and that charge transfer to the triazine fragment of the molecule is realized upon excitation. The degree of participation of the heterocyclic ring in the first electron transition, which is responsible for the color of the dye, decreases with an increase in the length of the polymethine chain.See [1] for Communication 14.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 985–991, July, 1988.     

Charge distribution and 13C NMR spectra of cyanine dyes with bridging groupings in the chromophore

The electronic structure of cationoid and anionoid cyanine dyes was calculated by the CNDO/2 method. The calculation results were compared with the data of the ¹³C NMR spectra. It was shown that the anionoid dyes of the malonocyanine class have all the inherent properties of a polymethine state, i.e., alternation of charges and leveling of bonds, and these are also characteristic of cationic streptopolymethines. According to the calculation data, the introduction of bridging groupings causes considerable changes in the electronic structure of the cyanine dyes, as confirmed by the results of the study of their ¹³C NMR spectra.Translated from Teoreticheskaya i Ékperimental'naya Khimiya. Vol. 23, No. 6, pp. 687–692, November–December, 1987.     

Conformation transformation barriers in linear donor-acceptor systems

The PM3 semi-empirical andab initio approximations have been used to calculate the equilibrium geometry and energy levels of donor-acceptor molecules that are derivatives of conjugated amines. Chain lengthening inverts the local level of the unshared nitrogen electron pair and the delocalized level, and also changes the sign of the barrier to rotation of the dimethylamino group in the excited state. Organic Chemistry Institute, Ukrainian National Academy of Sciences, 252660 Kiev 94, ul. Murmanskaya 5, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 224–228, July–August, 1997.     

Breaking of Symmetry of Solitons in the Ion-Radicals of α,ω-Disubstituted Polyenes

Quantum-chemical calculations in the AM1 approximation were made for the optimized geometry and also the electron and spin density distributions in the ion-radicals of ,-substituted polyenes [R—(CH=CH) _n —R]^±·. It was found that a soliton (of hole or electron type) with half-integral spin forms waves for the and components of the electron density, in contrast to the wave for the charges in the ions of polymethine dyes with a closed electron shell, containing a zero-spin soliton. The introduction of terminal groups of medium electron-donating power [—NH₂,—C(CN)₂] leads to the breaking of symmetry of the soliton at n2, whereas in unsubstituted polyenes the symmetrical geometry and symmetrical distribution of the electron and spin density are retained irrespective of the length of the conjugation chain.     

Location of charge and geometric soliton waves in dications of α,ω-substituted polyenes

A quantum-chemical investigation of the location and form of the solitons in the dications of polyenes was undertaken. It was shown that two soliton waves (both charge and geometric) in opposite phases are generated in the doubly charged conjugated systems; they coincide in form with that for the solitons in the single-charge π systems. In the dications of polyenes with a long chain both solitons are repelled from each other. In short chains a minimum distance is maintained between them, and both centers of the soliton waves can even be outside the molecule. The introduction of hydroxy or phenyl terminal groups into the dications of the polyenes leads to displacement of the centers of the charge and geometric waves without substantially distorting their form. The introduction of an amino group or tropylium residue is accompanied by displacement of the solitons to the end of the conjugation chain so that half of the soliton waves projects onto the molecule. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 272–278, September–October, 2008.     

A quantum-chemical study on the structures of linear conjugated systems that absorb in the near IR range

Calculations have been performed in the AM1 approximation on the equilibrium geometry, charge distribution, and energy levels of [R−(CH)_m−R]² symmetrical conjugated systems in which z=0, ±1, ±2; R=CN₂, NH₂, O; m=1÷46; the symmetrical structure is disrupted in a long molecule having an odd number of CH groups. In a long even-numbered system, there are two parts in which there are bond equalization and substantial charge alternation, which features are also characteristic, of odd systems, and in which they differ from neutral even ones, which have a uniform electron-density distribution and CC bond length alternation. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 3, pp. 150–154, May–June, 1999.     

W-Commensurability

Properties of the set of solutions (P, Q) of the equation [P, Q] = W in a free group are discussed in the paper, here W is any fixed nonempty group word.