Cyclic conjugation in annelated perylenes

Abstract

Cyclic conjugation in benzo-annelated perylenes was studied by means of the energy–effects of their six-membered rings. Several currently used models for assessing the extent of cyclic conjugation in benzenoid hydrocarbons, based on Kekul´e structures, Clar formulas, or conjugated circuits, predict that there is no cyclic conjugation in the central, “empty”, ring of perylene and its annelated derivatives. We show that in some annelated perylenes the extent of cyclic conjugation in the “empty” ring becomes unexpectedly high. Therefore, in the case of these annelated perylenes the Kekul´e–structure–based models fail.