Effects of polydispersity on fluorescence quenching in micelles

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Abstract
The effects of polydispersity on fluorescence quenching in micelle systems are discussed theoretically. Predictions are tested on computer generated fluorescence decay data for quenching in polydisperse micelle systems. It is shown that the estimated parameters, i.e, aggregation numbers and rate constants, are highly dependent on the micelle size distribution, and on the dynamic properties of the solubilizate–micelle system. Two extreme cases are considered: a static one, where no size changes of the micelles occur during the residence time, and a dynamic one where very large size variations take place. In the static case, the estimated aggregation number will decrease with quencher concentration from the weight average aggregation number in the limit of zero quencher concentration. In the dynamic case, the number average aggregation number is obtained, independent of quencher concentration. The initial decay constant contains information about the aggregation numbers, and in the generated data, this could be used to indicate the presence of polydispersity. Data from a number of experiments with the single photon counting technique are presented and analyzed according to the presented theory.