Cyclic Conjugation in Benzo-Annelated Perylenes. How Empty is the “Empty” Ring?

Abstract

Cyclic conjugation in benzo-annelated perylenes is studied by means of the energy-effects of their six-membered rings. “Classical” theoretical approaches (based on Kekule structures, Clar formulae, or conjugated circuits) predict that the central ring in benzo-annelated perylenes is “empty” and thus negligibly contributes to cyclic conjugation. Our calculations show that this is true only to a limited degree. In particular, rings angularly annelated relative to the central ring significantly increase the extent of its cyclic conjugation.