Electronic excitation transport and trapping in micellar systems: Monte Carlo simulations and density expansion approximation

Abstract

A theoretical treatment of electronic energy transport and trapping in a finite volume is presented by taking, as a typical example, an ensemble of chromophores solubilized in a spherical micelle. A truncated power series expansion in the chromophore density is used to calculate the configurational average of G S( t), the probability that an initially excited donor molecule is still excited, and G D( t), the probability of finding an excitation in the sub-ensemble of donors at time t, which are directly related to experimental observables. A detailed analysis of the problem via a Monte Carlo simulation is carried out for different occupation numbers of donor and trap molecules in a micelle, and for different ratios of the micelle radius to the Förster radius. The density expansion, as checked against the numerical results, provides a quite reasonable approximation, especially at short times and low chromophore concentrations. The difference in energy transfer dynamics between a finite and infinite volume system is described. The theory developed can be useful for probing structural details of microdisperse systems via time-resolved fluorescence measurements.