Cationic organic dyes (phenosafranine, safranine T (ST + ), thiopyronine, and methylene blue) are efficient quenchers of the triplet states of aromatic ketones. The triplets of benzophenone (BP), xanthone, thioxanthone, benzil, and N-methylacridone are quenched by the dyes via energy transfer, generating triplet excited dyes (typically k q ) 5.5 × 10 9 M -1 s -1 for 3 BP * + ST + in acetonitrile solution). Regarding Michler's ketone, p-(dimethylamino)benzophenone, and 3,6-bis(dimethylamino)thioxanthone, the mechanism of triplet quenching is solvent-dependent. Electron transfer occurs in polar solvents like acetonitrile, and energy transfer is the dominant reaction pathway in less polar solvents, such as dichloromethane. Delayed fluorescence of the dye caused by heterotriplet-triplet annihilation involving ketone and dye was detected upon studying the reaction of the dyes with triplet excited ketones (BP, xanthone, thioxanthone, and benzil). By applying two successive laser pulses (λ ex ) 532 and 308 nm, respectively), the rate constant of the reaction 3 BP * + 3 (ST + ) * was determined: k ht ) 1.1 × 10 10 M -1 s -1 .

The utilization of a photoinitiator system for radical polymerization which is based on decahydroacridine-1,8-dione and iodonium salt is shown. Differences of the initiation mechanism in two monomer systems are discussed: (a) in a solution of methyl methacrylate in acetonitrile measured by means of dilatometry and (b) in a 20-µ film of a multi-acrylate system measured by means of IR spectroscopy. The quantum yields of polymerization, ?, and the maximum polymerization rates, ®*1, are compared with those values of the well-known initiators working through o-cleavage.

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