Photochemistry of 1,4-anthraquinone studied by steady-state and laser-flash photolysis

Photochemical reactions of 1,4-anthraquinone (1,4-AQ) whose lowest triplet state (T-1) is of the pi, pi* type have been investigated in solution by me ans of steady-state and nanosecond laser flash photolyses. The absorption s pectrum of triplet 1,4-AQ in the non-polar solvent is determined for the fi rst time. The triplet state 1,4-AQ is quenched by the ground-state 1,4-AQ i n CCl4 to generate a dimerized product. In cycloalkanes, the final products obtained upon photoirradiation are adducts of the solvents to 1,4-AQ initi ated with the 1,4-AQ ketyl radical. The formation of the 1,4-AQ ketyl radic al originates from H-atom abstraction from cycloalkanes via the T-2 (n, pi* ) state which is in thermodynamic equilibrium with the T-1 (pi, pi*) state. In cycloalkenes and styrene, triplet 1,4-AQ gives the [2 + 2] cycloadducts forming the four-membered rings without H-atom abstraction. (C) 2001 Elsev ier Science B.V. All rights reserved.