Mechanism for Photocleavage of N-(Anthroyloxy)-9-fluorenylideneamines and Dynamic Behavior of Anthroyloxyl Radicals

Photocleavage of the N–O bond of N-(9-anthroyloxy)-9-fluorenylideneamine and its 1-and 2-anthroyloxy derivatives takes place efficiently in acetonitrile in the excited singlet state attributed to the fluorenylidene moiety. This made it possible for the first time to directly observe anthroyloxyl radicals by the transient absorption method. The quantum efficiency for photocleavage decreases remarkably in benzene, in which the lowest excited singlet state is attributed to the anthroate moiety. All the three kinds of anthroyloxyl radicals are much less reactive in decarboxylation, addition to olefins, and hydrogen-atom abstraction than benzoyloxyl and 1- and 2-naphthoyloxyl radicals; 9-anthroyloxyl radicals supposedly undergo intramolecular addition–elimination in the ipso-position in equilibrium with α-lactonic spirodihydroanthryl radicals, as indicated by one-color and two-color laser photolyses.