Kristin Weidemaier

Solvent structure and hydrodynamic effects in photoinduced electron transfer

A previously developed statistical mechanical theory describing photo‐induced electron transfer and geminate recombination in liquid solutions has been modified to account for realistic finite‐volume solvent effects. This work introduces physically important effects caused by the solvent which fundamentally affect the rates and spatial distribution of charge transfer events. The finite volume of solvent molecules gives rise to a nonuniform distribution of particles around an electron donor, which is incorporated into the theory by a two‐particle radial distribution function (rdf). The Percus–Yevick solutions for the rdf can give numerically useful values for the solvent structure, g(R) although any form of g(R) can be used with the method. The nonuniform particle distribution significantly affects the electron transfer rates and the distribution of ion pairs formed by forward electron transfer, particularly at short times. In addition, finite solvent size affects the rate of relative diffusion between any...

Photoinduced electron transfer between donors and acceptors on micelle surfaces

Abstract Fluorescence time-dependence and fluorescence yield data are used to examine photoinduced electron transfer between N,N-dimethylaniline and octadecylrhodamine B on the surfaces of dodecyltrimethylammonium bromide (DTAB) and Triton X-100 micelles. The data are analyzed with a detailed theory that includes diffusion of the chromophores over the micelle surface and models the reaction rate by a distance-dependent Marcus form. Good agreement between theory and experiment is obtained for reasonable choices of the transfer parameters for DTAB. However, for Triton X-100, there is reasonable agreement between theory and experiment only for values of the parameters that verge on unphysical. Possible explanations are discussed.

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

A detailed theoretical analysis of photoinduced electron transfer and geminate recombination on the surface of a spherical micelle is presented. An exact point‐particle analytical theory is first developed for one donor and N competing acceptors in random fixed positions on the micelle surface. The method is applicable to any restricted geometry system. Starting with a neutral donor and acceptors, the time dependent probability of having an excited neutral donor and the time dependent probability of having ions are calculated for various numbers of acceptors and various forward and back electron‐transfer parameters. The theoretical results are compared to Monte Carlo simulations of the problem, and the exact agreement obtained demonstrates that the ensemble averages are properly performed. Comparison is also made to a previously reported approximate analytical theory. The analytical theory and the Monte Carlo simulations are then extended to include the effects of donor–acceptor and acceptor–acceptor excl...

Effect of chromophore diffusion on electronic excitation transfer in micellar systems

Abstract An analytical theory and Monte Carlo simulations are used to study electronic excitation transport (EET) among chromophores diffusing on the surface of spherical micelles. The effect of molecular diffusion on the experimental observables is analyzed for two limiting cases, donor-trap (DT) and donor-donor (DD) EET. Analytical expressions are given for the time-dependent ensemble averaged survival probability of the excited donor P ( t ) in the DT case. Diffusion is found to have a pronounced effect on the excitation transfer kinetics except when chromophores have long Forster transfer distances R 0 and short fluorescence lifetimes.

Electron Transfer in Solution: Theory and Experiment

Photoinduced electron transfer is a fundamental chemical process. Following the transfer of an electron from an electronically excited donor to an acceptor, the resulting radical ions can go on to do useful chemistry. Electron back transfer (geminate recombination), however, quenches the ions and prevents further chemistry from occurring. The initial steps of photosynthesis involve excitation of a donor followed by electron transfer. Electron back transfer to the primary donor would stop the photosynthetic process. However, a specialized spatial array of consecutive acceptors eliminates the back transfer problem and is responsible for the efficiency of photosynthesis [1, 2, 3]. In systems of randomly distributed donors and acceptors (liquid or solid solutions) geminate recombination can be very rapid [4]. In liquid solutions, geminate recombination competes with diffusional separation of the photoinduced ions and limits chemical yields. Therefore, understanding phenomena which influence back transfer is not only an important basic problem, but is a problem of considerable practical significance.