Laser Flash Photolysis in High-Speed Photopolymer Coating Layers

The sensitization mechanisms of two systems of ketocoumarin dyes with a radical-generating reagent (10,10′-carbonylbis[1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano [6,7,8-ij]quinolizin-11-one] (KCD-J), 3,3′-carbonylbis]7-(diethylamino)coumarin] (KCD-DA) with 3,3′,4,4′-tetrakis(t-butyldioxycarbonyl)benzophenone (I) in poly(methylmethacrylate) film) and of two systems of coumarin dyes (10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one (CD-J), 3-(2-benzothiazolyl)-7-(diethylamino)coumarin (CD-DA) with I in the film) have been investigated by laser flash photolysis using a total-reflection cell. The fluorescence of the dyes was efficiently quenched by I with static quenching distances of 8.1, 8.6, 15.0, and 10.9 Å for KCD-J, KCD-DA, CD-J, and CD-DA. The decay time of the triplet was moderately quenched by I with a quenching rate (kq) of 5.8 × 105 mol−1 dm3 s−1 for KCD-DA, and slightly with a kq of less than 1 × 105 mol−1 dm3 s−1 for KCD-J; none of the triplet was detected on CD-J and CD-DA. These results suggested that a static sensitization from the fluorescent-excited dyes to I is predominant in photoinitiation systems.