Strong Coupling in Orthogonal Nanographenes

We report the cyclodehydrogenation of octaphenyl cyclooctatetraene on molten alkali metal, proceeding through six sequential cyclization steps to form a bay-fused dimer of dibenzoperylene, DBP. This molecule represents a well-defined junction between armchair edges of graphene subunits with controlled electronic coupling. The pronounced steric congestion at the molecular core generates a rigid structure composed of two orthogonally fused nanographene sheets-a structure that we designate as DBP[2]. Despite orthogonality, the nanographene moieties in DBP[2] exhibit strong electronic coupling. Spectroscopic and electrochemical measurements demonstrate electronic delocalization and robust inter-subunit coupling. The canonically disallowed communication across an eight membered ring gives rise to a pronounced chiroptical response ((|g_abs| ≈ 0.01 and |g_lum| ≈ 0.01) in the persistently chiral enantiomers of DBP[2]. DBP[2] is an efficient two-electron acceptor and shows pronounced absorption throughout the visible spectrum. More broadly, the novel cyclodehydrogenation reaction on molten alkali metals provides access to a broader class of contorted nanographenes for optoelectronics, energy storage, and chiroptical applications.