Molecular assembly with a figure-of-eight nanohoop as a strategy for the collection and stabilization of cyclo[18]carbon.

The recently synthesized novel figure-of-eight nanohoop with two strained oligoparaphenylenes (OPPs) was theoretically designed to collect and stabilize new allotropic carbon cyclo[18]carbon (C) through molecular assembly. The size adaptability and shape complementarity of C to OPP make it possible for them to combine into extraordinary ring-in-ring supramolecules. Thermodynamic analysis of 2C@OPP showed that the host-guest complex should spontaneously form below 404 K. Molecular dynamics (MD) simulations demonstrated that the assembly of C and OPP into host-guest complexes of up to 1 : 2 can occur at ambient temperature. Various real-space function analyses revealed that the nature of the non-covalent interaction between C and OPP is the van der Waals (vdW) attraction characterized by π-π stacking. Photoexcitation makes the host-guest complexes less stable in their S state by causing the central linker to flatten.