| Abstract | Dibenzocycloheptadienone (1) undergoes Norrish type I a-cleavage from both its first excited singlet state and an upper triplet state with quantum yields of 0.02 and 0.04, respectively. The major product in both cases is dihydrophenanthrene formed by loss of carbon monoxide from the initial biradical, followed by ring closure. The triplet state of ketone 1 has been characterized by laser flash photolysis. Photolysis of the triplet leads to irreversible bleaching and the generation of a short-lived (-350 ns) transient at 325 nm, which is tentatively assigned to biradical 3. |
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