A method for analyzing the cyclic electron delocalization interaction between different rings in polycyclic molecules

Abstract There are many theoretical and experimental approaches which can be used to assess the extent of cyclic electron delocalization in polycyclic conjugated compounds. On the other hand, methodologies capable of measuring how electron delocalization in the given ring is influenced by the presence of some other ring within the same molecule have attracted considerably less attention. To address this problem, a simple method, the so‐called pairwise fragment interaction (PFI) was put forward and discussed. The PFI is defined thorough the bond orders between the atoms belonging to different rings within the given molecule. In a series of benzo‐annelated anthracene and acridine derivatives it was demonstrated that the proposed PFI method can provide both, qualitative and quantitative relations between the information extracted from the density matrix and different indices which measure structural, energetic, electron delocalization and magnetic aspects of aromaticity.