Determination of the stern-volmer constant in quantum systems with dual fluorescence

The mathematical relations describing the properties of the steady-state spontaneous emission of quantum systems with dual fluorescence under conditions of dynamic quenching of excited states by foreign impurities are analyzed. The direct dependence of the intensity and yield of the photoproduct fluorescence on the quencher concentration is not simple and cannot serve as a convenient base for determining the Stern-Volmer constant. It is shown that, in the case of a kinetic character of product formation, the fluorescence intensity ratio of the initial dye and its photoproduct linearly increases with the quencher concentration. The relation obtained can be used to determine the constant of bimolecular quenching of the excited states of reaction products. This conclusion is based on the analysis of the experimental fluorescence spectra of 3-hydroxyflavone, obtained upon excitation in the region of the S ₁ absorption band under conditions of dynamic quenching by potassium iodide. This analysis can be applied to a wide range of luminophores with photoreactions accompanied by dual fluorescence (charge transfer, proton transfer, phosphorescence, complexation, etc.).