Boosting the Host-Guest Binding by Programming the Curvature in Geodesic Nanoribbons

The curvature of an aromatic system is an essential parameter that can be used to program the self-assembly and host-guest complementarity in geodesic polyarenes. However, the challenging synthesis of curved aromatics impedes exploration of the related effects on the binding properties. The design and synthesis of a polyarene with programmed curvature fitting to C₆₀ by a stepwise introduction of five-membered rings are presented to solve this challenge. Among several methods explored, the route utilizing cyclodehydrofluorination proved to be the most successful, in terms of the highest product yield. The binding studies suggest that fine-tuning the curvature in acyclic systems leads to a dramatic increase in affinity, embedding specific binding modes and selectivity, as revealed from the comparative studies with C₆₀ and C₇₀. Experimental and theoretical investigations with curved polyarenes of different sizes show that the buried surface area upon binding has a linear correlation with the binding energies. The curvature complementarity appeared to play a decisive role in achieving selective recognition of C₇₀ via the formation of a 2:1 complex along the major axis with an overall constant of 10⁸ M^-2 and positive cooperativity. The developed nanoribbons bearing the curvature of C₆₀ is the first all-carbon host showing binding affinities for fullerenes that are comparable with macrocyclic [10]CPP. The obtained data pave the way for understanding the properties of geodesic polyarenes and the design of new self-assembled materials based on fullerenes, nanotubes, and other curved structures.