Effects of chromophore interaction in photophysics and photochemistry of cyanine dyes

Abstract

Spectral and fluorescent properties of ketocyanine dyes (polyenic bis-ω,ω′-aminoketones) and cation-anionic polymethine dyes of various structures were studied. The symmetric ketocyanines were shown to have a long-wavelength absorption band bathochromically shifted in comparison with that of the asymmetric ketocyanines with the same total length of the polyenic chain. The nonlinear ketocyanines exhibit the additional short-wavelength band in their absorption spectra, which can be more intense than the longwavelength band. The absorption spectra of ion pairs of cation-anionic dyes with overlapping cation and anion bands contain a new intense short-wavelength band inactive in fluorescence excitation. These spectral peculiarities are explained on the basis of chromophore interaction model. It has also been shown that theT1levels of ketocyanine chromophores do not essentially interact with each other in a ketocyanine molecule in nonpolar solvents; in polar solvents this interaction becomes appreciable due to lowering the potential barrier for conjugation.

Effects of chromophore interaction in the spectroscopy of ketocyanine dyes with a central pyranone or pyridone fragment

“…As mentioned above, the S-S absorption spectra of dye 6 consist of two bands: an intense short-wavelength band and a much less intense long-wavelength band ( Figure 1 The positions of these bands, their intensity ratio, and the energy splitting (∆ν) between the S 1 and S 2 levels were explained in terms of interaction of two aminopolyenic chromophores in the dye molecule. The chromophores composing the dye (halves of dye 6 from the NMe 2 fragment to the carbonyl group) are oriented at an acute angle with respect to each other [2][3][4]. We found that the replacement of the O atom in the pyranone ring of ketocyanine 6 by the NMe group (dye 1) led to a dramatic change in the absorption spectrum of the dye (Figure 1).…”

“…Due to simple structures, these compounds appeared to be convenient for modeling various photophysical and photochemical processes. Recently we have studied the photonics of a number of ketocyanines, both simple and having a central pyranone fragment [1][2][3][4]. Their spectral and photophysical properties can be well explained in terms of the theory of chromophore interaction based on dipole-dipole interaction.…”

“…Conjugation between the dye chromophores has also a strong effect on the absorption spectra of ketocyanines [5][6][7]. It was revealed that the absorption bands of symmetrical ketocyanines (containing two aminopolyene fragments of the same length) are shifted bathochromically with respect to those of the unsymmetrical dye with the same total length of the polyene chain [1,3]. In contrast to the linear ketocyanines, an additional short-wavelength band is observed in the absorption spectrum of the dyes in which the chromophores are arranged at an angle to each other [2,4].…”

Spectral properties and conformations of nonlinear ketocyanines

“…We have earlier 1-5 studied a series of the ketocyanine dyes (polyenic ω,ω´ bisamino ketones) with the central pyranone or pyridone moiety (1,2) and the polymethine salts corresponding to these dyes (3,4).…”

“…6,7 Based on the concepts of the theory of chromophore in teraction and the experimental ratio of intensities of the long and short wavelength bands, we assumed that mol ecules 1 and 3 exist in the nonlinear conformation (1´ and 3´, respectively) in which the chromophores (polyene chains extending between the NMe 2 and carbo nyl groups) of the dyes are arranged at an acute angle to each other. [1][2][3] The question about the predominant conformation of compounds 2 and 4 remains unanswered, because their absorption spectra consist of a broad poorly re solved band.…”