Dicyclohepta[<i>cd</i>,<i>ij</i>]‑<i>s</i>‑indacene-Based\nNonbenzenoid Polycyclic\nHydrocarbons: Synthesis and Optoelectronic Properties

Two nonbenzenoid polycyclic hydrocarbons (PHs) bearing\none or two\ndicyclohepta[<i>cd</i>,<i>ij</i>]-<i>s</i>-indacene (DCHI) units were successfully synthesized via palladium-catalyzed\nintramolecular cyclization. In contrast to the well-known indeno[1,2-<i>b</i>]fluorene skeleton, the as-formed DCHI substructures not\nonly lead to their highly contorted conformations but also significantly\ncontribute to their modulated aromatic structures and optoelectronic\nproperties, such as decreased energy gaps, red-shifted light absorption,\nand multi-reversible oxidation activity, thus revealing the importance\nof such nonbenzenoid π extension.