PHOTOCHEMISTRY OF 1,2,3-INDANETRIONE*

The photochemistry of 1,2,3-indanetrione (1) has been examined in solution at room temperature by steady state and laser flash photolysis. The triplet state of 1 (T = 6.5 μs, δ_mux, = 360 and 570 nm, in dry acetonitrile) reacts preferentially via an a-cleavage process followed by a considerably slower loss of carbon monoxide. Triplet 1 shows a remarkably fast hydrogen abstraction rate constant when in the presence of 1,4-cyclohexadiene (k_r= 1.4 times 10⁶M^?1s^?1) in spite of its low excitation energy (E_T= 42 kcal/mol). This behavior can be explained by assuming that the vicinal carbonyls coplanar to the ketyl radical play an important role in its stabilization.