Anomalous cyclic conjugation in the perylene/bisanthrene homologous series

摘要

The homologous series of benzenoid hydrocarbons, whose first members are perylene (P1), bisanthrene (P2), and tetrabenzo[bc,ef, kl,no]coronene (P3), are usually considered as consisting of to two polyacene fragments, joined by essentially single carbon-carbon bonds, forming "empty" rings, devoid of any cyclic conjugation. In higher members of this series, the pattern of cyclic conjugation is found to be significantly different from that predicted by means of Kekule-structure-based models. Various measures of local aromaticity (NICS, HOMA, SCI), calculated at the B3LYP/6-311 + G(d,p) level of DFT theory, all indicate that cyclic conjugation in the "empty" rings in the middle of the molecule has a high value, exceeding those in the rings of the polyacene fragments. This anomaly begins at P4 and was demonstrated to exist at least until P7.