Dynamic quenching of the multiband fluorescence of 3-hydroxyflavone

The properties of emission, absorption, and dual fluorescence excitation of 3-hydroxyflavone in acetonitrile are studied under the conditions of dynamic quenching by potassium iodide with concentrations up to 4 × 10^?2 M. The normal and tautomeric forms undergo quenching, which is more efficient for the tautomeric form. An interesting circumstance is that the absorption in the S ₀ → S ₁ and S ₀ → S ₂ singlet bands of the solution increases with increasing quencher concentration in the whole region of concentrations used, the steepest rise being recorded in the concentration region from 0 to 5 × 10^?3 M. The intensities and quantum yields of the two fluorescence bands show rather complicated nonlinear dependences on the quencher concentration. The long-wavelength fluorescence band, which belongs to the tautomeric form of 3-hydroxyflavone, is quenched considerably stronger. The experimental results reveal the kinetic character of the excited-state proton transfer in molecules of 3-hydroxyflavone in acetonitrile.