BODIPY-directed dynamic covalent templating of carbon nanohoop rotaxanes with near-unity Förster resonance energy...

Mechanically interlocked carbon nanostructures remain an underexplored frontier in carbon nanoscience, largely due to the substantial synthetic challenges inherent to constructing such topologically complex architectures. Herein, we report a BODIPY-directed dynamic covalent templating strategy for the efficient assembly of rotaxanes. In this approach, F-BODIPY is installed onto a carbon nanohoop bearing a 2,2'-biphenol unit via nucleophilic substitution, affording a pseudo-rotaxane O-BODIPY derivative that serves as a key intermediate. Subsequent Sonogashira coupling with acetylenic stoppers yields the pre-rotaxane RxOB-1. Hydrogenation of the alkyne units in RxOB-1 produces RxOB-2, during which the O-BODIPY moiety undergoes cleavage and reconstitution to regenerate the F-BODIPY unit, ultimately delivering the target rotaxane RxFB-2. The structures of O-BODIPY intermediate 6 and RxOB-1 were unambiguously established by single-crystal X-ray diffraction analysis. Photophysical studies reveal that these (pre)rotaxanes exhibit high fluorescence quantum yields of up to 0.78, along with highly efficient Förster resonance energy transfer (FRET), with calculated energy transfer efficiencies approaching unity. Collectively, this work establishes a versatile synthetic platform for accessing mechanically interlocked carbon nanostructures.