Dicyclohepta[<i>cd</i>,<i>ij</i>]-<i>s</i>-indacene-Based Nonbenzenoid Polycyclic Hydrocarbons: Synthesis and Optoelectronic Properties

Two nonbenzenoid polycyclic hydrocarbons (PHs) bearing one or two dicyclohepta[<i>cd</i>,<i>ij</i>]-<i>s</i>-indacene (DCHI) units were successfully synthesized via palladium-catalyzed intramolecular cyclization. In contrast to the well-known indeno[1,2-<i>b</i>]fluorene skeleton, the as-formed DCHI substructures not only lead to their highly contorted conformations but also significantly contribute to their modulated aromatic structures and optoelectronic properties, such as decreased energy gaps, red-shifted light absorption, and multi-reversible oxidation activity, thus revealing the importance of such nonbenzenoid π extension.