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 the
T1 levels 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.
