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 C₁₂₈H₄₄. 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 C₇₀ is bound more strongly than C₆₀. The predicted host-guest binding energies of the (4,4), (5,5), C₆₀, and C₇₀ structures are 24, 43, 25, and 28 kcal/mol, respectively.