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

Abstract

With its unique chemical and physical properties, C₆₀ is an attractive molecule to be incorporated into molecular assemblies and supramolecular arrays. This paper reports the syntheses of a C₆₀ derivative with the macrocyclic polyether dibenzo-24-crown-8 (DB24C8) attached to the carbon sphere and of a C₆₀ adduct with a dibenzylammonium salt covalently bonded to the carbon allotrope. The C₆₀ DB24C8 conjugate forms a stable, pseudorotaxane-like 1∶1 complex (ΔG° = –16.6 kJ mol^–1, T = 298 K, CDCl₃–CD₃CN 1∶1) with dibenzylammonium hexafluorophosphate. Evidence for this superstructure was provided by ¹H NMR spectroscopic studies in solution and by mass spectrometric investigations in the gas phase. Equally, the C₆₀ dibenzylammonium conjugate threads through the cavity of DB24C8 to form a 1∶1 complex with a pseudorotaxane-like geometry (ΔG° = –23.3 kJ mol^–1, CDCl₃). Furthermore, the C₆₀ DB24C8 adduct and the C₆₀ dibenzylammonium conjugate interact with each other by means of hydrogen bonding and ion–dipole interactions to form the first supramolecular C₆₀ dimer (ΔG° = –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 C₆₀ 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.