An examination of diffusion-influenced fluorescence quenching by nearest quenching neighbors in liquids

The exclusive quenching of a potentially fluorescent species in solution by its nearest quenching neighbor imposes a finite upper integration limit to the flux equation and provides a modified version, i.e.

of the Smoluchowski-Collins-Kimball formulation of the Stern-Volmer equation. This is applied to data reported for the fluorescence quenching of two anthraquinone derivatives byN,N-dimethyl-p-toluidine in acetonitrile solutions of different (pressure-induced) viscosities. Values of the relative fluorescence quantum yields I₀/I(c) calculated from the above equation, using recovered values of the encounter diameter ϱ, the intrinsic quenching rate constant k⁰ and the viscosity-dependent diffusion coefficient D, agree with experimental data with an overall average deviation (2.7% for 53 data points) well within a reported experimental uncertainty of ±8%.