Losytskyy M. Spectral manifestations of the interaction of the cyanine dyes in water solutions and on the DNA surface

Thesis is devoted to the experimental study by the spectral methods of cyanine dyes aggregation processes in aqueous solutions, as well as formation of these dyes aggregates bound with DNA. It was established that the long-wave fluorescence of the studied monomethine cyanines in water solutions as well as in the presence of DNA belongs to the H-aggregates of these dyes. The abnormally big as for cyanine dyes Stokes shift of H-aggregates, as well as their wide unstructured fluorescence spectrum is believed to be connected with the transformation process that happens in an excited state of an aggregate. It was supposed that during this transformation an excimer state is formed between aggregate monomers. It is possibly, that the excimer state formation process is preceded by the excited aggregate nonradiative transition from the upper splitted excited level to the lower one. It was first established that the studied dyes TO, Cyan 13 and Cyan 40 form H-aggregates on DNA. The aggregates are formed by the interaction of the unbound dye molecule with the one already bound to DNA in monomeric form. It was first revealed that the trimethinecyanine dye Cyan beta-iPr selectively forms J-aggregates in the groove of DNA AT-sequences. In J-aggregates absorption spectra the davydov splitting is manifested. The spectrum of fluorescence excitation polarization revealed the different polarization of the electronic transitions corresponding to the two splitted J-aggregate bands. The study of absorption, fluorescence and fluorescence polarization spectra showed that the results obtained for Cyan beta-iPr J-aggregates are consistent with the Kasha model of electronic energy levels for helical aggregates. The long- and short-wave electronic transitions to the splitted J-aggregate excited levels are considered to be directed respectively parallel and perpendicular to the J-aggregate helix axis. The study of the fluorescence intensity time dependence, as well as the study of the spectral band width of monomers and J-aggregates showed that the electronic excitation in Cyan beta-iPr J-aggregates is delocalized over about 7-11 dye monomer units. The results of the study could be used and already partially do for the development of the DNA detection procedures, as well as for the specific detection of double-stranded AT-sequences of DNA.