The Dependence of the Electron-transfer Rates of Aromatic Hydrocarbon Anion Radicals upon the Molecular Radii of the Reactants

Abstract

Abstract The applicability of the theory of R. A. Marcus is tested, the behavior of the rate constant being examined as a function of the molecular radii of the reactants. The rate constants of the electron-transfer reactions from the anion radicals of pyrene, perylene, and tetracene to their respective parent molecules are measured under experimental conditions in which the anion radicals are in a free ion or loose ion-pair state. The rate constants thus obtained and subsequently corrected for diffusion are 2.8×109, 3.0×109, and 2.6×109 M−1sec−1 respectively, in 1,2-dimethoxyethane at 25°C. These rate constants, as well as others obtained elsewhere for naphthalene and anthracene, are compared with those predicted theoretically, assuming a spherical and an oblate spheroidal molecular shape. The consistence between the theoretical and experimental results is not satisfactory; the variation in the observed rate constants with the molecular radii of the reactants is much smaller than that expected theoretically. The spin-exchange rate constants for anion radicals of pyrene, perylene, and tetracene are also determined to be 7.0×109, 5.1×109, and 4.8×109 M−1sec−1 respectively, in the same solvent at 25°C.