Photochemical and Photophysical Behaviour of a Visible Photoinitiating System: Xanthenic Dye/Iron Arene Complex/Hydroperoxide/Amine

Rose Bengal (RB) is a versatile xanthenic dye which can be used as a photo-initiator of polymerisation in the presence of various additives such as an amine, an iron arene complex or a
hydroperoxide. Previous works showed that this photoinitiating system is very efficient for the photo-curing of thick pigmented coatings usable as paints in the wood furniture industry. The interaction between Rose Bengal (RB) or RB methyl ester and the iron arene complex (lrg(+)) or the additives was studied by steady state and laser flash photolysis experiments. A ground state complex between RB and lrg(+) is evidenced but not with RBMe. The first photochemical step is the reduction of lrg(+) within the complex leading to a highly reactive 19e complex. The photo-curing efficiency of the complex is compared to the physical mixture of RB/lrg(+).