The fluorescence quenching of S-2-xanthione and S-2-deuterated xanthione by 3,3-diethylpentane, cyclohexane, and deuterated cyclohexane in perfluoro-1,3-dimethylcyclohexane has been studied by means of a picosecond time-resolved, single-photon counting technique. The donor fluorescence decay in the presence of the quencher for six analyzed systems could satisfactorily be fit using the Smoluchowski-Collins-Kimball function. The molecular parameters: R (the sum of the molecular radii), D (the sum of diffusion coefficients), and the specific rate constant of the process (kappa) for all electronically excited donor-quencher pairs have been determined. The values of molecular parameter D, obtained from fluorescence quenching studies, are significantly lower than the sum of the macroscopic measured diffusion coefficients values. These results points to substantial differences in the rate of translational diffusion established in the molecular and macroscopic scale. The systems studied are proposed as model systems for further study of the time-dependent fluorescence quenching processes.