Effect of aggregates on the photochemical behavior of Rose Bengal peroxybenzoate initiator in PMMA film

To reveal the sensitization mechanism of Rose Bengal peroxybenzoate (RBBP) in poly(methyl methacrylate) (PM MA) film, the behavior of RBBP was investigated by means of both fluorescence spectroscopy and laser flash photolysis in PMMA as well as in dilute solution for comparison. In the RBBP concentration range 2 x 10(-3) to 9 x 10(-2) mol dm(-3) in PMMA film, the yields of the singlet and triplet excited states of RBBP are affected by dye aggregation which is enhanced by increasing RBBP concentration. Thus, in the (6-9) x 10(-2) mol dm(-3) RBBP concentration range, production of the fluorescent excited state is reduced, but formation of the triplet states is increased. This seems to be responsible for the radical generation during photoinitiation.