HYDROGEN-ATOM ABSTRACTION OF PARA-CHLORANIL TRIPLET IN 1,4-DIOXANE IN THE PRESENCE AND ABSENCE OF TETRACHLOROHYDROQUINONE

Mechanisms of hydrogen atom abstraction by triplet p-chloranil [GA(T)] from 1,4-dioxane (DOH) and tetra?chlorohydroquinone (CAH2) were studied in detail by means of nanosecond laser flash photolysis. A broad band around 740 nm in the transient absorption spectrum of GA in DOH was assigned to the charge-transfer band of the triplet EDA complex between GA and DOH. Efficiencies for the hydrogen atom abstraction from DOH and CAH2 were determined to be 0.13 and 0.58, respectively. The former value indicates that the hydrogen atom abstraction from DOH is less effective than a physical process in deactivation of the triplet complex. From the latter value together with the measured value of the quenching rate constant (1.7 × 109 dm3 mol-1 s-1) of the triplet by CAH2, it is inferred that the hydrogen atom abstraction of GA(T) from CAH2 takes place competing with an efficient radia-tionless deactivation via the triplet exciplex between GA(T) and CAH2 as a common intermediate.