Size-Selective Supramolecular Chemistry in a Hydrocarbon Nanoring

New-generation density functionals (M06-L and M06-2X) include an accurate treatment of medium-range correlation energy and have been applied to investigate host−guest interactions in supramolecular complexes in which a hydrocarbon nanoring, [6]paraphenyleneacetylene ([6]CPPA), acts as the host molecule. Guests include fullerenes and carbon nanotubes. The nature of the interactions has been discussed and analyzed. The size-selective supramolecular chemistry in the nanoring has been investigated by varying the size of the guest molecules and optimizing inclusion structures as large as C 128 H 44 . We found that the (5,5) armchair-type nanotube fits in the [6]CPPA hydrocarbon nanoring better than the (3,3) or (4,4) ones, and C 70 is bound more strongly than C 60 . The predicted host−guest binding energies of the (4,4), (5,5), C 60, and C 70 structures are 24, 43, 25, and 28 kcal/mol, respectively.