A novel [60]fullerene-calixarene conjugate which facilitates self-inclusion of the [60]fullerene moiety into the homooxacalix[3]arene cavity

A novel calixfullerene 1, in which a homooxacalix[3]arene moiety conjugates with a [60]fullerene moiety through a triethylene glycol chain, exhibits interesting self-complexation-decomplexation properties in response to the solvent polarity. In CDCl₃, 1 exists predominantly as conformer I with a free [60]fullerene moiety and the open calixarene cavity. In CHCl₃/CH₃CN (1:1, v/v), however, 1 exists predominantly as the self-inclusion conformer II with the [60]fullerene moiety capped by the intramolecular calixarene moiety. This is a unimolecular event but not an aggregate formation event because the concentration effect on the stoichiometry in the (1)H NMR spectroscopy and molecular weight determination in vapor pressure osmometry are all commensurate with a unimolecular process. The complexation-decomplexation exchange rate is slower than the NMR time scale, which has enabled us to estimate the equilibrium constant [conformer II/conformer I = 0.72 in CHCl₃/CH₃CN (24:1, v/v) at 27 °C].