PHOTOCHEMISTRY AND PHOTOINITIATION ACTIVITY OF RADICAL POLYMERIZATIONOF 2-SUBSTITUTED ANTHRAQUINONE DERIVATIVES .3. NANOSECOND LASER FLASH-PHOTOLYSIS STUDY

A nanosecond laser Hash photolysis study was undertaken on a selected range of 2-substituted anthraquinone derivatives and the data are disc ussed in relation to the photoactivities in industrial photopolymeriza tion. All the compounds give rise to a triplet-triplet absorption that is quenched by ground-state molecular oxygen. The transient half-live s range from 0.64 to 11.3 mu s of which the 2-(1,1-dibromomethyl)anthr aquinone exhibits the longest life time. In a reductive solvent, 2-pro panol, hydrogen atom abstraction takes place with the compounds having the lowest-lying tripler (3)n pi state, whereas those with a low-lyi ng triplet (3) pi pi state show mixed kinetics. In the latter case, a disproportionation reaction involving the semianthraquinone radical m ay be taking place, competing with the direct hydrogen atom abstractio n reaction. In addition, investigation of the halogenated derivatives has indicated the possibility of the corresponding halo radicals being formed. In the presence of a tertiary amine, triethylamine, all anthr aquinone derivatives show the formation of stable species related to e ither the exciplex or the radical ion pair. The extent of exciplex for mation is more effective with compounds possessing a lowest-lying trip let (3) pi pi excited state than those with a triplet (3)n pi* excite d state. The results from the nanosecond laser flash photolysis study show the differences in behavior toward hydrogen atom abstraction and electron transfer processes that is dependent on the nature of the low -lying tripler state and the type of substituent present, i.e., electr on-donating or electron-withdrawing. (C) 1996 John Wiley & Sons, Inc.