Fluorescence quenching of fluorescein with molecular oxygen in solution

The fluorescence quenching of fluorescein (FL) with molecular oxygen in alkali solution and in different solvents was investigated by steady-state absorption and fluorescence spectroscopy techniques. Fluorescence quantum yield (Φf), radiative rate constant (kr), fluorescence lifetime (τf), and non-radiative rate constant (knr) values were determined. Stern-Volmer equation was employed to calculate bimolecular quenching rate constants (kq) and, then, Smoluchowski equation was used for the determination of diffusion-controlled rate constants (kdiff) to compare with the experimental kq values. The temperature, quencher concentration, and solvent viscosity were experimental parameters to understand fluorescence quenching process of fluorescein with molecular oxygen in solution. Experimental findings indicated that the mechanism of fluorescence quenching is diffusive in nature.