High-Order Host-Guest Complexation of Structurally Well-Defined Cycloparaphenylene Double-Deckers with Fullerenes

Construction of high-order 2:2 complexes has not been reported for carbon nanohoop systems owing to the synthetic challenges of the host and the complexity of the binding process. In this work, a cycloparaphenylene double-decker host (1) was synthesized and its structure was determined by single-crystal analysis, revealing a trans-geometry and a self-assembled dimerization. Crystallographic studies and NMR/UV-vis titrations demonstrated the stepwise formation of a 1:2 complex between 1 and C₆₀. For the complexation of 1 and C₁₂₀, a highly cooperative 2:2 complex was formed, exhibiting the formation constant K _F = (1.2 ± 0.2) × 10¹⁷ M^-3; this complex disassembles into a 1:2 complex with the breaking constant K _B = (1.6 ± 0.3) × 10⁴ M^-1 upon addition of excess C₁₂₀. This distinctive binding-unbinding process is supported by single-crystal analysis, NMR titration, and diffusion-ordered NMR spectroscopy. The study highlights the potential of concave-convex π-π interactions in forming high-order complexes, which could facilitate the development of more sophisticated supramolecular architectures.