Rate constants of quenching of triplet excited ketones by several monomers were determined through time-resolved laser spectroscopy or culled from the literature. The semi-empirical calculation method PM3 allows the quenching mechanisms to be refined and can be used to predict the reactivity of aromatic ketones toward monomers. It is apparent from both experimental results and theoretical calculations that the rate constant (k(q)) measured for the bimolecular quenching between the triplet state of a given aromatic ketone and both electron-rich as well as electron-poor monomers, depends linearly on the free enthalpy of formation of the regioselectively favored 1,4-biradical, which is the primary reaction step of the ketone/monomer interaction.