Bowl on the ring: Molecular crowns hosting fullerenes synergistically by buckybowl and nanohoop

Abstract

Curved π-electron systems show unique properties and assembly feature that enable the specific applications in materials science and supramolecular chemistry. Herein, fullerene, carbon nanohoop and π-bowl are integrated by the coupling of covalent and supramolecular tactics. Firstly, π-bowl trichalcogenasumanenes (TCSs) are fused with a carbon nanohoop [10]CPP via covalent joint to form molecular crowns 4a/4b, which show structural and electronic complementarity and accordingly strong binding affinity to C₆₀/C₇₀. Secondly, the supramolecular assemblies of 4a/4b with fullerenes afford the host-guest complexes 4a/4b⊃C₆₀/C₇₀ in solution (molar ratio, 2:1) and solid state (molar ratio, 1:1). In the crystals of host–guest complexes, the intra-cluster and inter-cluster interactions are respectively dominated by the [10]CPP and TCSs moieties of 4a/4b. Additionally, it is found that 4a/4b are good photosensitizers for generating ¹O₂ and show structural adaptability in accordance to assembly conditions. 4a/4b take an endo-conformation in their own crystals with TCSs and [10]CPP moieties being bowl-shaped and elliptical, respectively. In contrast, the [10]CPP on 4a/4b changes into circular and the TCSs moiety becomes flat (for 4b) or shows bowl inversion to be exo-conformation (for 4a) in 4a/4b⊃C₆₀/C₇₀.