Molecular Basis for the Recognition of Higher Fullerenes into Ureidopyrimidinone-Cyclotriveratrylene Self-Assembled Capsules.

Fullerenes C60 , C70 , and C84 may be readily encaged within a hydrogen-bonded dimeric capsule, based on two concave cyclotriveratrylene (CTV) scaffolds, each containing three self-complementary 2-ureido-4-[1H]-pyrimidinone (UPy) subunits. NMR spectroscopy and circular dichroism studies, complemented by dispersion-corrected DFT calculations, are reported with the aim of characterizing such capsule-fullerene complexes both structurally and energetically. Six fullerenes are considered: in agreement with experiments, calculations find that encapsulation is most favorable for C84 (on a par with C90 ), and follows the trend C60 <C70 <C76 <C78 <C84 ≈C90 . As also found by NMR spectroscopy, the most stable capsules are formed by monomers of identical stereochemistry with UPy and the OMe groups of CTV in a mutual anti orientation and UPy-CTV ethylene linkers within the capsular surface plane. Up to C78 , encapsulation is favored by increasing host-guest contacts, but the trend is thereafter increasingly inhibited by growing capsule strain.