Theoretical understanding of stability of mechanically interlocked carbon nanotubes and their precursors.

Dispersion-corrected DFT calculations were performed on (,) nanotubes ( = 5-10) attached by a U-shaped functional group consisting of -xylene-linked double 9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydro anthracene terminated by CH chains ( = 6, 8, and 9), and their ring-closing macrocycles containing tubes. The reactant precursors and macrocycles are denoted by UP--(,) and (,)@Cycle-, respectively. We found that UP--(,) are energetically preferable relative to the dissociation limit toward a U-shaped functional group (UP-) and a tube (initial state) due to the attractive CH-π and π-π interactions.