Abstract: In this work, the photoreduction and the triplet quenching of ketocoumarin derivatives have been studied by laser flash photolysis method. When the amine was used as a triplet quencher, the ketyl radical of ketocoumarin can be observed evidently. Meanwhile, the transient absorption spectrum of ketyl radical has been recorded. Several kinds of olefinic monomers were also used as triplet quenchers. The quenching constants indicate that the quenching ability of monomers cannot be competed with that of amines. Therefore, it can be expected that ketocoumarin derivatives can photoinitiate polymerization of several kind of monomers which cannot be initiated by benzophenone.

Key words: ketocoumarin, photosensitization-initiation polymerization, electron and energy transfer, flash photolysis