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Nonsymmetric cationic polymethine dyes (tricarbocyanines) demonstrate dual emission which depends upon the dynamical properties of the solvent. In this study the symmetric and nonsymmetric polymethine dyes were investigated comparatively by light-absorption and fluorescence spectroscopy. In liquid solvents the narrow emission band at 758 to 762 nm is observed only, while in solid media the major emission component is at 720 to 740 nm, which depends strongly upon the solvent and the excitation wavelength. Both components are observed in the intermediate case of highly viscous media. These features become more significant with the increase of electronic asymmetry of the dye. The mechanism involving cis-trans isomerization in the exited dye molecule and reorganization of its solvate shell is proposed for the explanation of this phenomenon. The viscosity- dependent dual emission and convenient spectral range, which does not interfere with the spectra of cellular pigments, makes these dyes very promising in the studies of microscopic viscosity of biomembranes and the whole cells.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
