Davydov Splitting in Spectra of Cyanine Dye J-Aggregates, Formed on the Polynucleotides

It was found in our previous work (T. Y. Ogul'chansky et al. (2001) Spectrochimica Acta Part A57, 2705–2715) that the carbocyanine dye Cyan iPr forms J-aggregates in the groove of poly(dA)-poly(dT). In the present paper we study in detail the spectral properties and energy levels structure of the Cyan iPr J-aggregates by means of absorption and fluorescence spectroscopy and polarization measurements. The energy structure of an aggregate consists of at least two exciton zones, and dipole moments of the absorption transitions to these zones are oriented at an angle of about 90° one to another. It was supposed that the transition moment of the lower zone is parallel to the polynucleotide axis and the moment of the upper zone is perpendicular. The fluorescent transitions are possible only from the lower exciton zone, while the excitations of higher zone undergo nonradiative transitions to the lower one.