Analysis of transformations of the ultrafast electron transfer photoreaction mechanism in liquid solutions by the rate distribution approach

Abstract

Representation of the experimental reaction kinetics in the form of rate distribution is shown to be an effective method for the analysis of the mechanisms of these reactions and for comparisons of the kinetics with QC calculations, as well as with the experimental data on the medium mobility. The rate constant distribution function P(k) can be obtained directly from the experimental kinetics N(t) by an inverse Laplace transform. The application of this approach to kinetic data for several excited-state electron transfer reactions reveals the transformations of their rate control factors in the time domain of 1-1000 ps. In neat electron donating solvents two components are observed. The fastest component (k > 1 ps(-1)) was found to be controlled by the fluctuations of the overall electronic coupling matrix element, involving all the reactant molecules, located inside the interior of the solvent shell, rather than for specific pairs of reactant molecules. The slower component (1 > k > 0.1 ps(-1)) is controlled by the medium reorganization (longitudinal relaxation times, τL). A substantial contribution from the non-stationary diffusion controlled reaction is observed in diluted solutions ([Q] < 1 M). No contribution from the long-distance electron transfer (electron tunneling) proposed earlier for the excited-state electron transfer between perylene and tetracyanoethylene in acetonitrile is observed. The rate distribution approach provides a simple and efficient method for the quantitative analysis of the reaction mechanism and transformation of the rate control factors in the course of the reactions.

Competition and Interplay of Various Intermolecular Interactions in Ultrafast Excited-State Proton and Electron Transfer Reactions

“…There are several fitting procedures for recovery of the distribution of rate coefficients P ( k ) (a Laplace original) from the experimental kinetics N ( t )/ N (0) (a Laplace image). ,− In a general case, the direct inversion of the Laplace transform for recovering of the arbitrary probability densities of the rate coefficients P ( k ) has serious shortcomings, related to numerical instability, when the experimental data are intrinsically noisy. , This is related with a general property of inverse Laplace transform–the inverse transform of an experimental data set, which is inevitably incomplete and noisy, leads to ambiguity in P ( k ). A multitude of distribution functions will agree equally well with the experimental data.…”

“…Recently, some of us have shown that the nonexponential kinetics of ultrafast ET reactions in liquid solutions is related to the competition of several rate control factors: (1) the wide distributions of ET rate coefficients P ( k ET ) (for k ET ≈ 0.1–2 ps –1 ) caused by fluctuations of the electronic coupling matrix element ( V AD ) for reactant molecules located inside in the interior of the solvent shell; (2) reorganization of the medium and reactant molecules (in the range of the dielectric relaxation times); and (3) nonstationary diffusion of the reactant molecules (for k Diff [ Q ] ≈ 0.001–0.03 ps –1 ). In viscous solvents (η > 5 cP), some contribution of electron tunneling outside the interior of the solvent shell is also possible.…”

Electron Transfer Kinetics between an Electron-Accepting Ionic Liquid and Coumarin Dyes

“…However, subsequent computational studies ,− ,− of quenching in neat conventional liquids point to a fundamental shortcoming of such a model for treating neat-solvent quenching. Instead of a single nearby partner, in neat redox-active liquids, the fluorophore is surrounded by multiple reactive partners.…”

Interaction of α-diimine–chromium(III) complexes with non-ionic surfactant Triton X-100

“…The study of such systems has been a continuous interest area. In the literature, there are many works that report the interaction of a-diimine-ruthenium(II) ðRuðNNÞ 2þ 3 Þ complexes to different micellar media [5][6][7][8][9][10][11] as well as the influence of these interactions on the reactions with various compounds [12,13]. Moreover, the photochemistry and photophysics of a-diimine-chromium(III) ðCrðNNÞ 3þ 3 Þ complexes have been extensively studied in homogeneous systems [14,18], whereas there are, to the best of our knowledge, only a few works in micellar systems.…”