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 frequency domain fluorescence quenching rates. Equations are derived that relate the Laplace transform, k0(z), of the quenching rate coefficient 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(mf)(omega). These relationships can be useful in calculating steady-state 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 equivalent to an equation derived by Szabo (J. Phys. Chem. 1989, 93, 6929). The 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 between the steady-state, time-dependent, and frequency-dependent quenching rates illustrate a more general principle: the molecular rate coefficient, k(t), of a diffusion-controlled bimolecular process is coupled to the rates of concurrent unimolecular processes, e.g., particle generation and decay.