RELATIONS AMONG STEADY-STATE, TIME-DOMAIN, AND FREQUENCY-DOMAIN FLUORESCENCE QUENCHING RATES

Methods of nonequilibrium statistical thermodynamics are used to study relations among rate expressions for steady-state, time domain, and f requency domain fluorescence quenching rates. Equations are derived th at relate the Laplace transform, k0(z), of the quenching rate coeffici ent in the time domain, k0(t), to the steady-state rate constant, k(ss ), and to the mean field rate coefficient in the frequency domain, k(m f)(omega). These relationships can be useful in calculating steady-sta te and frequency domain results when the Laplace transform, k0(z), is given. The equation linking k0(z) with k(ss) is a rigorous consequence of the statistical nonequilibrium thermodynamic theory and is equival ent to an equation derived by Szabo (J. Phys. Chem. 1989, 93, 6929). T he equation relating k0(z) to k(mf)(omega) is obtained for the case of low illumination intensity and is different from that conjectured by Zhou and Szabo (J. Chem. Phys. 1990, 92, 3874). The relationships betw een the steady-state, time-dependent, and frequency-dependent quenchin g rates illustrate a more general principle: the molecular rate coeffi cient, k(t), of a diffusion-controlled bimolecular process is coupled to the rates of concurrent unimolecular processes, e.g., particle gene ration and decay.