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

The study is devoted to investigation of a number of ketocyanine dyes (polyenicω,ω′-bisaminoketones) with a central pyranone or pyridone fragment and respective polymethine salts by UV-VIS absorption and NMR spectroscopies. It was found that replacement of bridging O atom with NMe group suppresses the chromophore interaction in the cross-conjugated ketone and corresponding tridecamethine salt. Furthermore, incorporation ofmeso-amino substituent into the polymethine chain of the salts with the central pyrylium fragment sharply decreases the chromophore interaction. In spite of dramatic differences between the absorption spectra of the ketocyanines containing O- or NMe- bridging fragment,13CNMR spectra of these dyes are similar. A comparison of the differences between the chemical shifts of adjacent polymethine carbon atoms in the13CNMR spectra for these dyes point to stronger alternation of charges along the polymethine chain and, consequently, stronger chromophore interaction for the dye with the central pyrylium cycle. Flash photolysis experiments showed photoisomerization of the dyes with NMe bridging group to form long-lived isomeric form.

Effects of chromophore interaction in photophysics and photochemistry of cyanine dyes

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.