Photoinduced Electron Transfer and Geminate Recombination in Liquids

Abstract

The coupled processes of intermolecular photoinduced forward electron transfer and geminate recombination between donors (rubrene) and acceptors (duroquinone) are studied in two molecular liquids: dibutyl phthalate and diethyl sebacate. Time-correlated single-photon counting and fluorescence yield measurements give information about the depletion of the donor excited state due to forward transfer, while pump-probe experiments give direct information about the radical survival kinetics. A straightforward procedure is presented for removing contributions from excited-state-excited-state absorption to the pump-probe data. The data are analyzed with a previously presented model that includes solvent structure and hydrodynamic effects in a detailed theory of through-solvent electron transfer. Models that neglect these effects are incapable of describing the data. When a detailed description of solvent effects is included in the theory, agreement with the experimental results is obtained. Forward electron transfer is well-described with a classical Marcus form of the rate equation, though the precise values of the rate parameters depend on the details of the solvents' radial distribution function. The additional experimental results presented here permit a more accurate determination of the forward transfer parameters than those presented previously.1 The geminate recombination (back transfer) data are highly inverted and cannot be analyzed with a classical Marcus expression. Good fits are instead obtained with an exponential distance dependence model of the rate constant and also with a more detailed semiclassical treatment suggested by Jortner.2 Analysis of the pump-probe data, however, suggests that the geminate recombination cannot be described with a single solvent dielectric constant. Rather, a time-dependent dielectric constant is required to properly account for diffusion occurring in a time-varying Coulomb potential. A model using a longitudinal dielectric relaxation time is presented. Additionally, previously reported theoretical results 3 are rederived in a general form that permits important physical effects to be included more rigorously.

Experimental and Theoretical Analysis of Photoinduced Electron Transfer: Including the Role of Liquid Structure

“…Additionally, work is currently in progress analyzing the ion kinetics from pump probe data. 101 The ion kinetics provide an additional check of the reliability of the forward transfer parameters. This occurs because successful analysis of the ion state probability requires a detailed knowledge of the ion distribution created by forward transfer.…”

Solvent Reorganization Energy and Free Energy Change for Donor/Acceptor Electron Transfer at Micelle Surfaces: Theory and Experiment

“…The combined problem of forward electron transfer and geminate recombination has been studied. [45][46][47][48] The same considerations that are treated here for forward transfer apply to the distancedependent back transfer rate.) The region inside the smaller circle contains the surfactant tails and is the hydrocarbon core.…”

Ultrafast electron transfer, recombination and spin dynamics

“…A thorough analysis of this time dependence is beyond the scope of this Letter (for a recent treatment of the problem see Ref. [18]). To get an idea of the timescales involved in the quenching process, the experimental data were fitted to a multi-exponential decay function convoluted with an instrument response function B(t-t o) centered at to:…”