COMPARISON OF THE SMOLUCHOWSKI APPROACH WITH MODERN ALTERNATIVE APPROACHES TO DIFFUSION-INFLUENCED FLUORESCENCE QUENCHING - THE EFFECT OF INTENSE EXCITATION PULSES

For low intensity excitation pulses, the fluorescence intensity in the presence of quenchers is obtained, within the framework of the Smoluc howski approach, by convoluting the pulse profile with the survival pr obability of an excited fluorophore initially surrounded by an equilib rium distribution of quenchers. This conventional approach is generali zed to handle excitation pulses of arbitrary intensity. The resulting expression is exact in the limit that the,fluorophore is static and th e quenchers diffuse independently. Modern alternative approaches to th is problem are based either explicitely or implicitely on truncating t he reduced many-particle distribution function hierarchy by means of a superposition approximation. For a delta-function excitation pulse al l approaches yield the identical result. For arbitrary pulses, the mod ern 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 app roximation that is made in the modern approaches. (C) 1997 American In stitute of Physics.