On the conditions needed to verify a nonstationary diffusion model by kinetic analysis of fast fluorescence quenching

Abstract

Numerical experiments were carried out to test the feasibility of distinguishing fluorescence quenching kinetics based on the treatment of Smoluchowski, Collins and Kimball (SCK) from those showing single-exponential decays (Stern-Volmer kinetics) for a series of emission lifetimes lower than 1 ns corresponding to the measured lifetimes for seven thioketones in perfluoro-1,3-dimethylcyclohexane as solvent. Experimental apparatus functions have been used to simulate the decays. The results show that it is possible to determine the parameters of the SCK decay curve using appropriate equipment with short excitation sources and a detector with adequate time resolution and using the nonlinear least-squares fitting technique, provided the emission lifetime τ is longer than the duration of the nonstationary diffusion phase. Correlation coefficients are determined between the SCK function parameters, which explain the difficulties often encountered in fitting decay curves to SCK theory. Parameter uncertainties have been estimated from a series of simulations which experimentalists can use to ensure the parameters, which they obtain from fitting fluorescence decay curves in the presence quenchers, are valid and not interdependent.