Electron Acceptors Based on Functionalizable Cyclopenta[<i>hi</i>]aceanthrylenes and Dicyclopenta[<i>de,mn</i>]tetracenes

We report the synthesis and selective functionalization of two externally fused cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs) and demonstrate their electron accepting behavior. 2,7-Bis­(trimethylsilyl)­cyclopenta­[hi]­aceanthrylene (1) and 2,8-bis­(trimethylsilyl)­dicyclopenta­[de,mn]­tetracene (4) were prepared in a one-pot, palladium-catalyzed cross-coupling of (trimethylsilyl)­acetylene and either 9,10-dibromoanthracene or 5,11-dibromotetracene, respectively. The trimethylsilyl groups were selectively converted into bromides via substitution with N-bromosuccinimide to create universal partners (2 and 6) for metal-catalyzed cross-coupling reactions. To demonstrate the utility of the halogenated CP-PAHs, we successfully employed a Sonogashira cross-coupling between the CP-PAHs and a phenylacetylene derivative. The resulting compounds (3 and 7) were found to be highly conjugated between the CP-PAH core and the substituents, as demonstrated by large bathochromic shifts in the absorption spectra as well as density functional theory calculations. Ethynylated CP-PAHs 3 and 7 were found to possess low optical bandgaps (1.52 and 1.51 eV, respectively) and displayed two reversible reductions. We further demonstrated the fullerene-like electron-accepting behavior of 3 through solution-phase fluorescence quenching of the prototypical electron donor, poly­(3-hexylthiophene).