Polycyclic Hydrocarbons from [4n]Annulenes: Correlation versus Hybridization Forces in the Formation of Diradicaloids

The conceptual connections between [4n] Hückel antiaromaticity, disjoint orbitals, correlation energy, pro-aromaticity and diradical character for a variety of extended π-conjugated systems, including some salient recent examples of nanographenes and polycyclic aromatic radicals, are provided based on their [4n]annulene peripheries. The realization of such structure–property relationships has led to a beneficial pedagogic exercise establishing design guidelines for diradicaloids. The antiaromatic fingerprint of the [4n]annulene peripheries upon orbital interactions due to internal covalent connectors gives insights into the diradicaloid property of a diversity of π-conjugated molecules that have fascinated chemists recently.J.C. thanks MINECO/FEDER of the Spanish Government (PGC2018-098533-B-100, PID2021-127127NB−I00 and RED2018-102815-T) and the Junta de Andalucía (UMA18FEDERJA057). M.K. and M.M.H. acknowledge the NSF (CHE-2107820 to M.K., CHE-1954389 to M.M.H.) for financial support. We thank the anonymous reviewers for their helpful comments. Funding for open access charge: Universidad de Málaga / CBU