Structure of complex systems using electronic excitation transport: Theory, Monte Carlo simulations, and experiments on micelle solutions

Abstract

Monte Carlo (MC) simulations and an analytical theory are presented to describe electronic excitation transport (EET) among static chromophores constrained to lie on the surfaces of spherical micelles. Both donor–trap (DT) and donor–donor (DD) EET are examined for two types of systems: probe molecules on the surfaces of isolated (low concentration) micelles, and probes on the surfaces of interacting (concentrated) micelles. The EET dynamics are described by the function, 〈G s(t)〉, the probability of finding the excitation on the originally excited chromophore. For the isolated micelle calculations, the excitation dynamics depend on the distribution of probes on a single hard sphere surface. For the interacting micelle calculations, the hard sphere structure is accounted for by using the radial pair distribution function, g(r). Both single micelle and many micelle DT calculations do not involve approximations. Consequently, the DT expressions agree exactly with the MC calculations. For the DD calculations, a first order cumulant approximation is used to obtain analytically tractable solutions to 〈G s(t)〉. Padé approximants of the cumulant solution, accurate over a broad range of chromophore number and Förster interaction strengths, are used to describe DD EET on isolated micelles. For DD EET in many micelle systems, the first order cumulant approach is shown to be a suitable method for intermicelle structural studies. Both the cumulant and MC calculations are simultaneously compared to time resolved flourescence depolarization measurements performed on octadecylrhodamine B(ODRB)/triton X-100/water systems made in previous investigations.