Spiro[16]arene: A Spirocycle-Bridged Macrocycle With Nanocarbon Recognition

The development of new bridging chemistry for macrocyclic arenes is crucial for creating supramolecular hosts with well-defined structures and practical functions. In this work, we report a spirocycle-bridged macrocycle named spiro[16]arene (SP16). In contrast to conventional single- or double-stranded macrocycles, SP16 features polycyclic aromatic hydrocarbon units interconnected by spirocyclic bridges, which create two electron-rich quadrangular cavities above and below the mean macrocyclic plane. As a consequence, SP16 displays unique host-guest complexation chemistry for nanocarbon molecules, including an ability to bind [6]cycloparaphenylene ([6]CPP, at a 1:1 stoichiometry) and C₇₀ (at a 1:2 stoichiometry) both in solution and in the solid state. Moreover, due to the inherent rigidity of the spirocyclic bridge, rotation of the repeating units of SP16 is restricted, and its inherent chirality retained in solution. The enantiomers of SP16 could be resolved by chiral high-performance liquid chromatography and were found to display both circular dichroism and circularly polarized luminescence. This work expands the toolbox of macrocyclic bridging chemistry and opens up avenues for the future design of functional macrocycles.