EFFECT OF METAL-SALTS ON THE FLUORESCENCE OF IONIC DYES IN WATER SOLUTIONS

Energy transfer between the dye cations and lanthanide ions in concent rated water solutions of electrolytes is studied. It is found that the energy transfer is described by the diffusion mechanism and its rate constant is not affected by the solution structure and viscosity. A si multaneous decrease in tau(f) and I-f of trypaflavine with increasing concentration of CsCl is found. At the same time, LiCl, NaCl, and KCI do not affect these quantities. The diffusion mechanism of fluorescenc e quenching of cationic dye by an external heavy atom (Cs+) in water s olutions is proved. We attribute a nonlinearity of the trypaflavine fl uorescence quenching by Cs+ ions to the shielding of charges of intera cting ions by Cl- anions. It is found that Br- anions quench the trypa flavine fluorescence 5-10 times more effectively than Cs+ cations do. It is shown that fluorescence of fluorescin dianion is also quenched i n the presence of CsCl, but in this case the process occurs within ion ic pairs consisting of the dye and quenching cation, competing with ot her cations for the site in this pair. The assumption is advanced that an external heavy atom does not affect fluorescence of oxazine 1 dyes luminescing in the red and near IR regions because of the effective c ompetition of internal conversion with intersystem crossing in them.