Abstract
The triplet quenching of anthracene and a,h-dibenzanthracene by four nitrobenzenes was studied by laser flash photolysis. Bimolecular quenching rate constants were determined in acetonitrile and methanol. They follow the expected free energy correlation for an outer sphere electron transfer process. The rate constants in methanol are generally higher than those in acetonitrile. The activation enthalpies and entropies were also measured in both solvents. The activation entropies are more negative in acetonitrile and the activation enthalpies are lower in acetonitrile with negative values being observed in some cases. Transient absorption spectra show that in the quenching process free radical ions are formed in methanol, but in acetonitrile free ions are almost absent. These results are compared with the current models for outer sphere electron transfer reactions. They cannot be explained if the solvent is considered as a dielectric continuum.
Published Version
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