Mechanically Interlocked Double-Walled Covalent Organic Framework with Cucurbit[8]Uril-Stabilized Viologen Radical...

The stabilization and functional integration of organic radicals within crystalline frameworks remain a significant challenge in materials chemistry, particularly for applications in optoelectronics and sensing. Herein, we report the design and synthesis of a radical-rich, polyrotaxanated covalent organic framework (VCB COF) featuring viologen-based radical cation dimers mechanically interlocked within cucurbit[8]uril (CB[8]) macrocycles. This supramolecular architecture gives rise to a double-walled framework that significantly enhances radical stability, photophysical properties, and photoresponsivity. Electron paramagnetic resonance (EPR) analysis reveals that VCB retains over 72% of its radical signal after 7 days of air exposure, compared to just 22% in its nonrotaxanated analogue, TpV COF. Photophysical studies reveal a 3-fold increase in photoluminescence intensity, while photoelectrochemical measurements demonstrate a stable photocurrent density of 1.3 μA cm-2 under 405 nm illumination with reversible on/off switching. Molecular dynamics simulations together with solid-state NMR support the localization of CB[8] at COF junctions and are consistent with the formation of a double-walled architecture stabilized by dipolar and long-range noncovalent interactions. This work establishes a generalizable strategy for integrating persistent radicals within COFs through macrocycle-assisted encapsulation and mechanical bonding, opening new avenues for the development of robust photoactive, redox-active, and spin-functional materials.