Plas Coch, Wrexham, Clwyd L11 2AW, U.K.; and 31nstituto de Ciencia y Tecnologia de Polimeros, C.S.I.C., c/]uan de la Cierva 3, 28006 Madrid, Spain SYNOPSIS A nanosecond laser Hash photolysis study was undertaken on a selected range of 2-substituted anthraquinone derivatives and the data are discussed in relation t o the photoactivities in industrial photopolymerization. All the compounds give rise to a triplet-triplet absorption t h a t is quenched by ground-state molecular oxygen. T h e transient half-lives range from 0.64 to 11.3 ps of which t h e 2-(l,l-dibromomethyl)anthraquinone exhibits t h e longest lifetime. In a reductive solvent, 2-propanol, hydrogen atom abstraction takes place with t h e compounds having t h e lowest-lying triplet 'hx* state, whereas those with a low-lying triplet 3 x x * state show mixed kinetics. In t h e latter case, a disproportionation reaction involving t h e semianthraquinone radical may be taking place, competing with t h e direct hydrogen atom abstraction reaction. In addition, investigation of t h e halogenated derivatives has indicated the possibility of t h e corresponding halo radicals being formed. In t h e presence of a tertiary amine, triethylamine, all anthraquinone derivatives show the formation of stable species related to either t h e exciplex or t h e radical ion pair. T h e extent of exciplex formation is more effective with compounds possessing a lowest-lying triplet 37r7r* excited state than those with a triplet 3 n~* excited state. T h e results from the nanosecond laser flash photolysis study show t h e differences in behavior toward hydrogen atom abstraction and electron transfer processes t h a t is dependent on t h e nature of the low-lying triplet state and the type of substituent present, i.e., electron-donating or electron-withdrawing.
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