Ketocoumarins as photosensitizers and photoinitiators

Several 3‐ketocoumarins with alkoxy or dialkylamino substituents in the 7 position, which are efficient sensitizers for crosslinkable polymers, were evaluated as photoinitiators. Proper combinations of certain derivatives of these ketocoumarins with activators such as amines, acetic acid derivatives, and alkoxypyridinium salts gave quantum yields for initiated radical polymerization much higher than that obtained from the Michler's ketone/benzophenone combinations. For each class of activators the dependence of the efficiency of polymerization on the redox properties of the ketocoumarins is explained in terms of charge transfer or electron transfer from the activator to the excited ketocoumarin (acetic acid and amine activators, respectively) or electron transfer in the opposite direction (pyridinium salt activators).