Radiolytic generation and photochemistry of 9-xanthenyl radicals in halogenated solvents

The photochemistry of 9-xanthenyl radicals produced by pulse radiolysis of xanthene in halocarbon was studied by means of a successive laser flash photolysis in the presence and absence of oxygen. In deaerated solutions rapid (during 6 ns laser pulse) and permanent photobleaching due to chlorine atom transfer from solvents to the excited 9-xanthenyl radical was observed with quantum yields of 0.04 and 0.26 in 1,2-dichloroethane and CCl₄, respectively. In the solutions containing oxygen, equilibrium between 9-xanthenyl radicals and peroxyl radicals was established and recovery of the photobleached 9-xanthenyl radicals was observed, which was accounted for by dissociation of peroxyl radicals. The whole reaction scheme of formation and decay of 9-xanthenyl radicals in CCl₄ is discussed based on the kinetic simulations.