Expanded Helicenes: A broad new class of carbon nanostructures

Chirality in carbon nanostructures (CNSs) gives rise to fascinating properties, including non-linear optical responses, circularly polarized absorption and emission, and rich supramolecular and solid-state chemistry. Helicenes can be considered the prototypical chiral CNS and have thus been the focus of tremendous recent interest. We recently reported the first study on a broad new compound class, the expanded helicenes, which contain larger π-systems than typical helicenes and possess an internal cavity. We are actively engaged in a systematic investigation of this compound class, enabled by a scalable, divergent, metal-mediated [2+2+n] cycloaddition synthetic strategy. Initial investigations have revealed remarkable supramolecular chemistry, including a diastereoselective dimerization via π-stacking, which was observed both in solution and in the solid state. In contrast to most reported helicenes, the π-framework in expanded helicenes is highly flexible. We are currently investigating factors that affect configurational stability and employing the new synthetic method to rationally control supramolecular organization and electronic properties. Future efforts will also involve applications of these compounds in organic electronics and catalysis.