For low intensity excitation pulses, the fluorescence intensity in the presence of quenchers is obtained, within the framework of the Smoluchowski approach, by convoluting the pulse profile with the survival probability of an excited fluorophore initially surrounded by an equilibrium distribution of quenchers. This conventional approach is generalized to handle excitation pulses of arbitrary intensity. The resulting expression is exact in the limit that the,fluorophore is static and the quenchers diffuse independently. Modern alternative approaches to this problem are based either explicitely or implicitely on truncating the reduced many-particle distribution function hierarchy by means of a superposition approximation. For a delta-function excitation pulse all approaches yield the identical result. For arbitrary pulses, the modern approaches predict different. albeit numerically similar, results. This difference, however, does not constitute an improvement over the Smoluchowski approach. Rather, it is a reflexion of an additional approximation that is made in the modern approaches. (C) 1997 American Institute of Physics.
