Direct edge functionalization of corannulene-coronene hybrid nanographenes

Abstract

For more than a century, electrophilic aromatic substitution reactions have been central to the construction of a rich variety of organic molecules that are useful in all aspects of human life. Typically, small aromatic nuclei, such as benzene, provide an ideal substrate. An increase in the number of annulated aromatic rings enhances the number of potential reactive sites and frequently results in complex product mixtures. Thus, nanographenes with a relatively large aromatic system are seldom selective in their substitution positions. Moreover, nanographene substrates with a scope for multiple substitution reactions and patterns remain rare. Herein, we demonstrate that a curved aromatic system based on a corannulene-coronene hybrid structure comprising 48 conjugated sp 2-carbon atoms allows for direct and regioselective edge functionalization through bromination, nitration, formylation, and Friedel-Crafts acylation in good yields. The postsynthetically installed functional groups can be modified through versatile organic chemistry transformations, including (mechanochemical) Suzuki-Miyaura, Sonogashira-Hagihara, and Buchwald-Hartwig amination reactions. Furthermore, the substitutions can be carried out in a sequential manner to yield heterofunctional structures. The edge-functionalization strategy enables modular access to nanostructures with appealing properties, such as strong fluorescence emission in the visible and near-infrared regions (475-900 nm) with record Stokes shifts (>300 nm), at an exceptionally small carbon footprint (C48).