The self-assembly of fullerene-containing [2]pseudorotaxanes:: formation of a supramolecular C60 dimer

With its unique chemical and physical properties, C-60 is an attractive molecule to be incorporated into molecular assemblies and supramolecular arrays. This paper reports the syntheses of a C-60 derivative with the macrocyclic polyether dibenzo-24-crown-8 (DB24C8) attached to the carbon sphere and of a C-60 adduct with a dibenzylammonium salt covalently bonded to the carbon allotrope. The C-60 DB24C8 conjugate forms a stable, pseudorotaxane-like 1:1 complex (Delta G degrees = 16.6 kJ mol(-1), T = 298 K, CDCl3-CD3CN 1:1) with dibenzylammonium hexafluorophosphate. Evidence for this superstructure was provided by H-1 NMR spectroscopic studies in solution and by mass spectrometric investigations in the gas phase. Equally, the C-60 dibenzylammonium conjugate threads through the cavity of DB24C8 to form a 1:1 complex with a pseudorotaxane-like geometry (Delta G degrees = 23.3 kJ mol(-1), CDCl3). Furthermore, the C-60 DB24C8 adduct and the C-60 dibenzylammonium conjugate interact with each other by means of hydrogen bonding and ion-dipole interactions to form the first supramolecular C-60 dimer (Delta G degrees = 17.0 kJ mol(-1), CDCl3-CD3CN 90:10). In all three cases, the dibenzylammonium component is threaded through the cavity of the crown ether macrocycle. When DB24C8 is complexed to the C-60 dibenzylammonium conjugate, the luminescence associated with the catechol rings of the crown ether is partially quenched upon complex formation. We have profited from this special feature to monitor reversible, acid-base induced dethreading/rethreading processes.