Annelated perylenes: Benzenoid molecules violating the Kekulé-structure-based cyclic conjugation models

Abstract

Several currently used models for assessing the extent of cyclic conjugation in benzenoid hydrocarbons, all based on Kekulé-type structural formulas predict that there is no cyclic conjugation in the central, "empty", ring of perylene and its annelated derivatives. In this paper it is shown that in some annelated perylenes the cyclic conjugation in the "empty" ring (measured by its energy-effect) may be unexpectedly high. Therefore, in the case of these annelated perylenes, the Kekulé- structure-based models fail. The cause for such an "anomalous" behavior of annelated perylenes is discussed.