The photochemistry of 1H-benz[f]indane-1,2,3-trione (1) in the presence of olefins has been examined in benzene solution at room temperature by laser flash photolysis. The triplet excited state of 1 (tau = 3 mus, lambda = 460 and 490 nm, in benzene) is quenched by olefins containing allylic hydrogen with rate constants ranging from 10(5) L mol-1s-1 (for 1,5-hexadiene) to 10(9) L mol-1s-1 (for 2,5-dimethyl-2,4-hexadiene). A comparison of the reactivity of 1 with that of 1,2,3-indantrione (2) shows that a similar mechanism for the quenching by olefins is operating for the two cyclic vicinal triketones and involves essentially the lowest triplet excited state of n,pi* character.
cyclic vicinal triketone; laser flash photolysis; triplet state
