Electronic excitation transfer in concentrated micelle solutions

Abstract

Electronic excitation transport among interacting clusters of chromophores is investigated as a function of chromophore and cluster concentration. The technique of time-correlated single photon counting is employed to obtain time-resolved fluorescence depolarization data on aqueous octadecylrhodamine B/triton X-100 micelle solutions. The time-dependent fluorescence anisotropy, the energy transport observable, is directly compared to a theory developed to model this system. The theory is based on a first-order cumulant approximation to the solution of the transport master equation. The model depicts the micelles as monodisperse hard spheres with chromophores (octadecylrhodamine B) distributed about their surfaces. At low micelle concentration, the dynamics of excitation transfer depend only on internal micelle structure. At high micelle concentration, excitation transfer occurs among chromophores on different micelles in addition to intramicelle transfer. The theoretical treatment provides nearly quantitative descriptions of the time and concentration dependence of the excitation transport. It correctly predicts the concentration at which intermicelle transfer becomes significant. In the low micelle concentration limit (energy transport confined to isolated micelles) the model having a Poisson distribution of chromophores works well for small v ([chromophores]/[micelle]), but progressively worse as v is increased. Following the literature, a chromophore interaction parameter (in the form of a two dimensional second virial coefficient) is used to skew the probe distribution. This enables the transport theory to reproduce the data for all the values of v investigated and provides a determination of the second virial coefficient.

Photoinduced electron transfer and geminate recombination on a micelle surface: Analytical theory and Monte Carlo simulations

“…29 The micelles are taken to be dilute, so that electron transfer from a donor on one micelle to an acceptor on another micelle is not considered. How-ever, micelle-to-micelle excitation transfer has been studied in detail, 30,31 and this electron-transfer theory could be extended in an analogous manner.…”

Monte Carlo simulations of electronic excitation transfer in polymer composites and comparison to theory

“…4-14͒ apply to systems of random copolymers, 4,6,15-18 micelle surfaces, 5,19,20 and the micellar, lamellar, and cylindrical phases of diblock copolymers, 7,8 making it possible to probe the architecture of a variety of polymer composites at the molecular level. Since the measurement of EET can involve the detection of single fluorescent photons, EET experiments afford a sensitivity that permits probing the configurations of copolymers which are present in a composite at very low concentrations.…”

Role of Diffusion in Photoinduced Electron Transfer on a Micelle Surface: Theoretical and Monte Carlo Investigations

“…We note that the results are particularly relevant for the analysis of experimental data. For example, recent experiments have studied electronic excitation transport among chromophores on micelles. , Analogous experiments could be performed for chromophores that undergo electron transfer, and the results will depend critically on whether the chromophores diffuse significantly on the time scale of the electron-transfer events. Importantly, experimental measurements of diffusion constants for chromophores in micelles have shown that these diffusion constants can be significant .…”