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  • 1
    Electronic Resource
    Electronic Resource
    Cis-trans-isomerization of cationic-anionic polymethine dyes (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 682-688 
    Details
    ISSN: 1573-9171
    Keywords: polymethine dyes ; cis-trans-isomerization ; ion pairs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of solvent polarity and ion pair formation oncis-trans-isomerization of cationic-anionic polymethine dyes and of related simple cationic and anionic dyes is studied by flash photolysis. The change in the rate constant for reversecis-trans- isomerization of photoisomers due to the interaction of a cation with an anion in an ion pair is observed in nonpolar solvents. A drop in the yield of the photoisomers to zero is observed for a number of cationic-anionic dyes in weakly polar and nonpolar solvents which is possibly due to steric hindrances in the photoisomerization process in ion pairs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00704002
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  • 2
    Electronic Resource
    Electronic Resource
    Study of the absorption spectra and ionic equilibria of cationic-anionic polymethine dyes (1992)
    Springer
    Russian chemical bulletin 41 (1992), S. 1985-1991 
    Details
    ISSN: 1573-9171
    Keywords: polymethine dyes ; absorption spectra ; ionic equilibria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The absorption spectra of a number of cationic-anionic polymethine dyes in polar, low-polarity, and nonpolar solvents were studied. It was established that in polar solvents the absorption spectra represent the sum of the absorption spectra of the cation and anion, whereas in nonpolar and low-polarity solvents, in many cases the appearance of a short-wave absorption band is observed, due to interaction of the chromophores of the cation and anion in ion pairs. In solvents of intermediate polarity (for example, in chloroform and ethyl acetate), a concentration dependence of the absorption spectra is observed, determined by the equilibria of ionic dissociation. The ionic dissociation constants of a number of cationic-anionic dyes in chloroform and ethyl acetate were determined by a conductometric method. The thermodynamic data obtained are compared with the spectral data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00863360
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  • 3
    Electronic Resource
    Electronic Resource
    Fluorescent properties of cationic-anionic polymethine dyes (1992)
    Springer
    Russian chemical bulletin 41 (1992), S. 1992-1997 
    Details
    ISSN: 1573-9171
    Keywords: polymethine dyes ; fluorescence spectra ; ion pairs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The fluorescence spectra were studied and the quantum yields of the fluorescence of a number of cationic-anionic polymethine dyes were measured in polar, low-polarity, and nonpolar solvents. It was shown that the fluorescence spectra of cationic-anionic dyes in polar solvents, like the absorption spectra, represent the sum of the fluorescence spectra of the corresponding cationic and anionic dyes. For dyes in which the absorption bands of the anion and cation are close and a new short-wave band arises in the ion pairs, excitation into this band virtually does not lead to fluorescence, which is a consequence of the forbidden nature of the long-wave transition that arises as a result of the interaction of the chromophores. For a number of cationic-anionic dyes in ion pairs an energy transfer is observed: When an ion possessing short-wave absorption is excited, an ion with long-wave absorption fluoresces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00863361
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  • 4
    Electronic Resource
    Electronic Resource
    Photochemistry of anionic polymethine dyes (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 677-682 
    Details
    ISSN: 1573-9171
    Keywords: polymethine dyes ; cis-trans isomerization ; ion pairs ; triplet state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Spectral and kinetic properties of photoisomers and triplet molecules of a number of anionic polymethine dyes, namely, differential absorption spectra, rate constants (k i ) and activation parameters of reversecis-trans-isomerization, and triplet-state-decay rate constantsk T are studied by flash photolysis. CINDP/2 calculations of electron density in anionic dyes show thatk i andk T in polar solvents are determined primarily by the electronic effect of the substituents in themeso-position of the polymethine chain of a dye. The increase ink i due to the formation of ion pairs consisting of a dye with a counterion is observed in nonpolar solvents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00704001
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  • 5
    Electronic Resource
    Electronic Resource
    Study of fluorescent aggregates of polymethine dyes (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 60-66 
    Details
    ISSN: 1573-9171
    Keywords: fluorescence spectra ; polymethine dyes ; aggregates ; ion pairs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Absorption, fluorescence, and fluorescence excitation spectra have been studied for a number of anionic, cationic, and cationic-anionic polymethine dyes in low-polar and nonpolar solvents, as well as in binary mixtures of solvents differing in polarity. For most of the dyes studied, fluorescent aggregates have been found to form. Their broad fluorescence bands are located in the long-wave region with respect to those of the initial dyes. The quantum yield of the aggregate fluorescence is normally higher than that of the initial dyes. Fluorescence excitation spectra of some cationic-anionic dyes in nonpolar solvents disagree with their absorption spectra because of contact and solvent-separated ion pairs simultaneously present in the solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00699975
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