Dicyclopenta[4,3,2,1‐ <i>cde</i> :4′,3′,2′,1′‐ <i>pqr</i> ]‐ <i>peri</i> ‐tetracene: Synthesis and an Example of Annulene‐within‐an‐Annulene Aromaticity in Different Redox States

Abstract We report a robust strategy for tuning the electronic structure and chemical stability of π‐conjugated polycyclic hydrocarbons (PHs). By fusing two cyclopentadienyl rings in the peri ‐tetracene bay regions, we introduce antiaromatic character into the π‐system, leading to unique photophysical and electronic properties. A stable mesityl‐substituted dicyclopenta‐ peri ‐tetracene derivative was synthesized through stepwise formylation/intramolecular cyclization at the bay regions of the dihydro peri ‐tetracene precursor, followed by oxidative dehydrogenation. This compound features an open‐shell singlet diradical ground state, global antiaromaticity, exceptional stability under ambient conditions, and amphoteric redox behavior with a small energy gap. Its dication also possesses an open‐shell singlet ground state, and its structure was identified by X‐ray crystallographic analysis, revealing a unique [14]annulene‐within‐[22]annulene global aromatic structure. In contrast, the dianion exhibits a closed‐shell singlet ground state. This work provides valuable insights for designing and synthesizing novel open‐shell PHs with tunable electronic structures and remarkable stability.