The strong binding in the (5,5)@[6]CPPA complex involves both medium-range dispersion-like attraction and orbital overlap. Note that even though the overlap is small in the (4,4)@-[6]CPPA complex, the interaction energy in (4,4)@[6]CPPA is
almost comparable to that in C60@[6]CPPA.
In summary, the supramolecular interactions in a hydrocarbon nanoring host, [6]CPPA, have been shown with recently developed density functionals to be very strong and size-selective. The density functional results in the present study are in agreement with experiments and a previous ab initio study for HMB@[6]CPPA, which, along with validation studies in Supporting Information, lends credibility to the predictions for larger complexes for which ab initio calculations are prohibitively resource consuming. We also calculated the interaction strengths of two supramolecules where the guest molecules are fullerenes and in three supramolecules where guest molecules are truncated nanotubes. The size selectivity
in the supramolecular complexes in which truncated nanotubes act as guest molecules results from the combined effect of dispersionlike attractive forces and e-electron overlap between the guest and host. Such overlap would be expected to enhance interfacial electronic charge transport.34-36 The ability of new density functionals to analyze and accurately model attractive interactions due to medium-range correlation energy opens new possibilities for computer-aided supramolecular design.
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