Author(s):
Costa, Sílvia M. B. 
; Maçanita, A. L. ; Formosinho, S. J.
Date: 1984
Persistent ID: http://hdl.handle.net/10316/10295
Origin: Estudo Geral - Universidade de Coimbra
Document details
Effective distances of exothermic charge-transfer reactions in the excited state
Description
A study of intermolecular, exothermic charge-transfer interactions is described. A distance dependence on the unimolecular charge-transfer rate constant k,,(R) is observed in viscous solvents where transfer at longer distances than the collisional one can compete with dissociation of an encounter complex. A comparative study of the quenching phenomena, occurring in a family of redox partners of aromatic esters and amines, was carried out in nonviscous solvents (hexane and acetonitrile) and viscous solvents (liquid paraffin/heptane mixtures and nonionic micelles of Triton X- 100). In the latter, the experimental reactional distances obtained are discussed in terms of effective distances R,ff, which are related to an average value of kct(Reff) for the reactant pair distribution function. A correlation of these distances with either the free activation energy, Act, or the diffusion coefficient D enables the estimation of an order of magnitude of parameters such as the average radii of donor and acceptor orbitals, L = (2.7 f 0.2) X cm, a preexponential factor at the collisional distance, k’,,(R,) = 3.7 X 10” d, an intrinsic reorganization parameter X = 0.64 eV, and an electronic matrix element V(Rc) N eV for the nonpolar media studied. An equation for kct(R), k,,(R) = koct(R,)e xp[-2(R - R,)/L] exp(-AG*/kB7+),d erived within the framework of a semiclassical theory, is used to discuss these interactions as equally nonadiabatic reactions to which an extended Marcus formalism is applied. http://dx.doi.org/10.1021/j150662a047
A study of intermolecular, exothermic charge-transfer interactions is described. A distance dependence on the unimolecular charge-transfer rate constant k,,(R) is observed in viscous solvents where transfer at longer distances than the collisional one can compete with dissociation of an encounter complex. A comparative study of the quenching phenomena, occurring in a family of redox partners of aromatic esters and amines, was carried out in nonviscous solvents (hexane and acetonitrile) and viscous solvents (liquid paraffin/heptane mixtures and nonionic micelles of Triton X- 100). In the latter, the experimental reactional distances obtained are discussed in terms of effective distances R,ff, which are related to an average value of kct(Reff) for the reactant pair distribution function. A correlation of these distances with either the free activation energy, Act, or the diffusion coefficient D enables the estimation of an order of magnitude of parameters such as the average radii of donor and acceptor orbitals, L = (2.7 f 0.2) X cm, a preexponential factor at the collisional distance, k’,,(R,) = 3.7 X 10” d, an intrinsic reorganization parameter X = 0.64 eV, and an electronic matrix element V(Rc) N eV for the nonpolar media studied. An equation for kct(R), k,,(R) = koct(R,)e xp[-2(R - R,)/L] exp(-AG*/kB7+),d erived within the framework of a semiclassical theory, is used to discuss these interactions as equally nonadiabatic reactions to which an extended Marcus formalism is applied. http://dx.doi.org/10.1021/j150662a047
Document Type
Article
Language English
Language English
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