The present paper is devoted to an investigation of the polymerization reactions in clear and pigmented curable coatings and describes the main reactions involved in a system which contains four components : a photosensitizer (Rose Bengal), an initiator (ferrocenium salt), an amine and a hydroperoxide. Interaction between Rose Bengal (RB) and the ferrocenium (Fc(+)) was studied by steady state and laser flash photolysis experiments. The contribution of static fluorescence quenching is evidenced by time resolved fluorescence experiments and can be explained by the occurrence of a ground state complex between RB and Fc(+). After light absorption by RB, the singlet excited state of RB is quenched within the RB/Fc(+) ion-pair leading to semi-oxidized RB and a 19e Iron Aren complex, Fc(0). In addition, the interaction of RB with an amine and cumene hydroperoxide is studied and the photochemical behaviour of a mixture containing the four components is discussed. A rather complete description of the interactions in the excited states is provided which outlines the key role of the in-situ generated reduced form of the initiator. This study allows to discuss the mechanism involved in a photoinitiating system capable of polymerizing thick pigmented coatings usable as paints in the wood furniture industry.
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