Principles of molecular design of binuclear polymethine systems

The electronic nature of reaction centers of reactants in the formation of polymethine compounds has been analyzed, and it has been established that the polymethine structures, depending on the combination of parity of the external polymethine chain and the signs of the electron-donor strength of the terminal heterocyclic nuclei, can be divided into two classes: classical polymethine dyes and generalized Hünig systems. In the generalized Hünig systems, the dependence of the charge distribution and bond orders in the polymethine chain on the difference in basicities of the terminal nuclei should be the opposite of the known relationships in a number of classical polymethine dyes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 307–314, May–June, 1990.     

Polymethine-polyene transition parameter in polymethine dyes

Within the framework of the HMO approximation and an equal bond model, quantitative characteristics are proposed for the alternation of electron density on the atoms and bonds of an unsubstituted chain of polymethine dyes with arbitrary end-groups. These characteristics can be used, depending on the type of electron distribution, to classify a compound as a polymethine or polyene. A structural parameter determined by the nature of the end-groups has been found, this parameter being responsible for realization of one type of electron density distribution or the other in the polymethine chain.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 129–138, March–April, 1988.     

Quantum-chemical investigation of the distribution of the electron density in asymmetric polymethine dyes

It has been shown with the use of the HMO, PPP, and CNDO/2 approximations that the distribution of the electron density in asymmetric polymethine dyes at the ends of the polymethine chain is determined mainly by the electron-donor ability of the nearby terminal groups, whereas in the middle their influence becomes weaker as the chain becomes longer. The asymmetry of the dyes causes a decrease in the alternation of the charges on the atoms and an increase in the alternation of the bond populations. These phenomena are most clearly displayed in the SCF approximations, which always emphasize alternation. The closer are the electron-donor properties of the terminal groups and the longer is the polymethine chain, the smaller is the difference in the distribution of the electron density near the terminal residues in asymmetric and symmetric dyes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 347–351, May–June, 1986.     

Effects of temperature on the fluorescence intensities of polymethine dyes

Raising the temperature even in a narrow range causes an appreciable fall in the fluorescence intensity for DODC and HIDC polymethine dyes. Quantum-chemical calculations lead one to interpret the temperature effects as due to an increase in the probabilities of rotation around the bonds in the polymethine chain on account of reduction in their orders on excitation.Organic Chemistry Institute, National Academy of Sciences of the Ukraine, 253094 Kiev, ul. Murmanskaya 5, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 4, pp. 220–223, July–August, 1996. Original article submitted November 30, 1995.     

Reaction of 3-formylchromone with methyl- and methylene-active azocycles

The reaction of 3-formylchromone with quaternary salts of nitrogen heterocycles containing active methyl or methylene groups was investigated. It is shown that the compounds obtained can be used in the synthesis of merocyanine dyes containing an o-hydroxybenzoyl substituent in the polymethine chain. Dicarbocyanines with such a substituent were not isolated, evidently because of the high electrophilicity of the polymethine chain and the ease of formation of a six-membered heteroring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1271–1275, September, 1990.     

π-Electron waves in binuclear polymethine compounds

An additive generative function method previously proposed has been used to derive analytic expressions for the charge and bond-order distributions in polymethine chains for binuclear polymethine compounds. The -electron wave amplitude is determined primarily by the electron-donor capacity in the terminal groups at the edges and in the difference of those capacities at the center. The electron-donor capacity governs the charge exchange between a terminal group and the chain in the ground state. That approximation gives a rigorous basis for the terms used in the literature: polymethine and polyene types of compound, as well as for the smooth transition between them.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 266–271, May–June, 1989.     

Synthesis of benzimidazole derivatives

Imidadicarbocyanines containing a chloro, bromo, or methyl group in the polymethine chain were synthesized in order to investigate their optical properties.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 254–257, February, 1975.     

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.     

Synthesis of benzimidazole derivatives. 11. Imidatricarbocyanines with substituents in the polymethine chain

In order to investigate their optical properties, imidatricarbocyanines of the benzimidazole series containing methyl, methoxy, and cyano groups as substituents in the polymethine chain have been synthesized.For communication 10, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 524–527, April, 1980.     

Synthesis and properties of substituted indolo-3,3′-trimethinecyanines

Some new indolo-3,3-trimethinecyanines, derived from 1,2-dimethyl and 1-methyl-2-arylindole and substituted in the external polymethine chain with halogen, methyl, aryl, and cyano, have been synthesized. The effects of the substituents in the external polymethine chain on the spectral characteristics of the indolotrimethinecyanines are discussed, taking into account delocalization of electron density in the chromophore and steric effects, together with the polarographic and photographic properties of these dyes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1652–1656, December, 1983.     

Effective length of benzannellated terminal groups in polymethine dyes

The effect of benzannellation on the effective length of the terminal groups was studied by the method of asymptotic nonbonding MOs in the approximation of dyes with an extremely long polymethine chain. Both alternant and nonalternant conjugated hydrocarbon systems were examined. The variation of the effective length in relation to the number of added benzene rings was investigated. It was shown that the effect of annellation can be assessed by using the concept of equivalent terminal groups and the theory of perturbations in the asymptotic nonbonding MOs of polymethine dyes. Examples of the extension of the obtained relationships to heterocyclic terminal groups are given. The proposed approach makes it possible to interpret the cases where benzannelation is accompanied by a hypsochromic effect.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 142–148, March–April, 1990.     

Dependence of the composition of the products of thermal fragmentation of thiacyanine dyes on the length of their polymethine chain

The pathways of thermal fragmentation of thiacyanine dyes with different lengths of the external polymethine chain were investigated. The results of thermolysis of the thiacyanines are compared with the results of quantum-chemical calculations of their molecules.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 188–192, February, 1982.     

Optimized bond lengths and electron densities on atoms in heterosubstituted polyenes

Bond lengths and electron density distribution in the polymethine chain of various heterosubstituted polyenes having carbonyl, cyano, and amino end groups are calculated in geometry-optimized CNDO/2 aproximation. It is shown that the significant alternation of the carbon-carbon bond lengths is largely independent of the nature of the end group, the arrangement of long and short bonds being determined by the form of the polyene. Heterosubstitution causes the electron density to alternate and the alternation amplitude, which decreases towards the middle of the chain, is dependent on the electron-donor properties of the polyene.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 4, pp. 313–319, July–August, 1992.     

Synthesis and spectral-generational characteristics of pentamethylidynecyanine dyes from 1-methyl-3-arylbenzo[f]quinolinium salts

Pentamethylidynecyanine dyes were synthesized by the reaction of 1-methyl-3-(R-phenyl)benzo[f]quinolinium quarternary salts with 1,3,3-triethoxy-1-propene, Pentamethylidynecyanines substituted in the meso position of the polymethine chain were obtained by condensation of these salts with 1-anilino-2-methyl-3-dimethoxy-1-propene hydrobromide. The spectral and generational characteristics of the dyes were determined. It was shown that the presence of a phenyl group in the benzo-[f]quinoline ring of the dyes gives rise to a bathochromic shift of the absorption and generation maxima. The investigated dyes have high generation efficiencies that lie in the 20–30% range and in the 940–1010 nm spectral range.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1523–1527, November, 1982.     

Quantum-chemical investigation of bond orders in symmetric polymethine dyes

The behavior of the bond orders in symmetric model polymethine dyes has been investigated by the HMO, PPP, and CNDO/2 methods. It has been established that the greatest equalization of the bonds is achieved in the case of dyes with moderately basic terminal groups. In other cases, alternation of the bond orders, which diminishes with increasing length of the polymethine chain and attenuates with increasing distance from the end, has been discovered at the ends of the polymethine chain. The amplitude of the alternation of the bond orders in a polymethine chain is greater, the more the basicity of the terminal groups, as characterized by the electron-donor parameter _o (0 _o 90°), deviates in either direction from the mean (_o = 45°). It is considerably smaller in the first excited state than in the ground state. The -electronic approximation is a correct method for describing the electronic structure of a polymethine chain. The neglect of the electrons can distort the bond orders of the terminal groups.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 138–146, March–April, 1985.     

The length of the polymethine chain and the spectral-luminescent properties of symmetrical cyanine dyes

The general characteristics that relate the length of the polymethine chain of symmetrical cyanine dyes to their spectral-luminescent properties depending on the electron-donor character of the heterocycles and the nature of the solvent are formulated. For various types of symmetrical cyanines, the Stokes shifts decrease with the elongation of the polymethine chain due to weakening of the vibronic interactions. The vinylene shifts of the band maxima are essentially constant and fall within the range 100 to 130 nm depending on the nature of the heterocycles and the solvent. When the polymethine chain elongates the fluorescence quantum yields first increase and then decrease. The greater the effective length of the heterocycle the stronger the decrease. The fluorescence decay occurring when the polymethine chain gets longer is associated with intensification of the internal conversion. For symmetrical cyanines, the changes in the shapes of the electronic bands (their width, asymmetry, excess, and fine structure) as the chain elongates are governed by the competing effects of the vibronic and intermolecular interactions. The former decrease as the chain lengthens, causing the narrowing of the absorption bands for the lower vinylogs. On the other hand, the latter increase as chain lengthens, which leads to broadening of the bands for the higher vinylogs. The higher the solvent nucleophilicity and the greater the deviation of the electron-donor ability of the heterocycle from the average value the greater the broadening. Any elongation of the polymethine chain of symmetrical cyanines causes only narrowing of the bands and an increase in the asymmetry, excess, and structuring in the fluorescence spectra, which, unlike the absorption spectra, is independent of the electron-donor character of the heterocycles and the nature of the solvent. These effects are caused by the fact that, in contrast to absorption, changes in the shape of emission bands with increasing chain length are governed predominantly by vibronic rather than by intermolecular interactions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1227–1239, July, 1994.     

PCILO calculation on the ansa conformation of hexahydrorifamycin S

PCILO calculation on the conformation of the 16, 17, 18, 19, 28, 29 hexahydrorifamycin S points to an ansa chain conformation of the C(12)–C(28) fragment from the alternatives given by a previous ¹H NMR spectroscopic study.The energetically favoured conformation of the C(19)–N fragment has also been determined.     

Research on polymerocyanines

A number of bis(nullomethylidyne)- and nullomethylidynedimethylidynedimerocyanines that are rhodanine derivatives with 3,3-dimethylindolenine, benzothiazole, 4,5-diphenylthiazole, and pyridine residues were obtained. The color of the dimerocyanines depends on the basicity of the nitrogen-containing heterocyclic residue and the length and position of the external polymethine chain. A sharp increase in the sensitizing ability is observed on passing from nullomethylidynedimethylidynedimerocyanines to dimethylidynenullomethylidynedimerocyanines.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1209–1212, September, 1977.     

Investigation of the distribution of the negative charge in anionic cyanine dyes by means of lanthanide shift reagents

It was established by PMR with lanthanide shift reagents that the charge in anionic cyanine dyes with a linear chromophore is concentrated at the ends of the polymethine chain, while in compounds containing a vinylene group in the chromophore it is concentrated in the region of the five-membered ring. The results are compared with the data from¹³C NMR spectroscopy and relaxation measurements in the presence of Gd(fod)₃. The validity of the conclusions is also considered.Kiev University. Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya, Vol. 27, No. 2, pp. 197–201, March–April, 1991. Original article submitted December 20, 1989.     

Synthesis of thiapenta- and thiahexacarbocyanine dyes from alkoxy-substituted polymethine salts with dimethylamine residues

The possibility of the use of alkoxypolymethine salts with dimethylamine residues to obtain thiapenta- and thiahexacarbocyanine dyes is demonstrated. The synthesis of a number of meso-alkoxythiapentacarbocyanines that contain various condensed rings in the 12 and 14 positions of the polymethine chain was realized, and their photographic properties were investigated. It was established that the dyes obtained are effective infrachromatic sensitizers. The electronic absorption spectra of the synthesized compounds were measured.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1631–1636, December, 1981.