Steady-state and fluorescence decay measurements have been carried out on aqueous solutions of poly(ethylene glycol)s made of a central chain spanning two pyrene labels and flanked by overhangs of various lengths. These decays,exhibit excimer formation kinetics which cannot be explained within the theoretical framework of the classic Birks＇ scheme. The decay analysis is complicated by the existence of hydrophobic associations between the pyrene groups. We have analyzed our time-resolved fluorescence decays by deriving a dynamic version of a model originally proposed by Char et al. (Macromolecules 1989, 22, 3177-3180) where the pyrene excimer is formed in a sequential manner. A diffusion process brings the two chromophores within a capture volume where the excimer is produced at a much higher rate. An analysis of our fluorescence decays based on this approach yields kinetic parameters which are consistent with the Char et al. model and earlier observations made on these systems. As the size of the overhang increases, the diffusion-controlled excimer formation rate decreases as was found previously in organic solvents, and the degree of association increases as well. The excimer formation process within the capture volume is very rapid. This quantitative analysis provides us with a detailed picture of these systems.