Tube-Diameter Dependent Potential Energy Surfaces of the Formation of Mechanically Interlocking Carbon Nanotubes

Mechanically interlocked carbon nanotubes (MINT) were formed on a specific diameter, but their mechanism has not been explored. This study employed dispersion-corrected DFT calculations to elucidate the MINT formation mechanism assisted by a separate carbide-Ru catalyst, clipping terminal vinyl groups bound to alkyl linkers with double π recognition groups connected to each other. The initial steps proceed near a terminal group to form a carbide-Ru catalyst bound to the linker (ring-open paths). The bound catalyst attacks the other terminal group, to form a C═C bond connecting both linkers, generating MINT (ring-closed paths). The changes in the potential energy surfaces (PESs) in the ring-closed paths depend on the tube-diameter, whereas those in the ring-open paths are independent. The PESs in the ring-close paths on a smaller-diameter tube (e.g (5,5) tube) are downhill, while those on a medium-diameter tube (e.g (6,6) tube) are uphill, but MINT formation is energetically feasible. A prominent destabilization of MINT is found in a larger-diameter tube (e.g., the (7,7) tube). These tube-diameter-dependent PESs originate from switching attractive or repulsive π–π interactions between a tube and a functional group whose void space becomes smaller with progression in the ring-close path, being key in the specific tube functionalization.