Covalent Organic Framework Bearing Persistent Radicals by Thermocyclisation of Backfolded Alkyne‐Rich Motifs ^†

Comprehensive Summary Open‐shell radicals, susceptible to quenching by self‐coupling, have found numerous practical applications in materials science and the medical field due to their high reactivity and rich photophysical and electronic properties. Porous and highly customisable crystalline frameworks, such as metal‐organic frameworks (MOFs) and covalent organic frameworks (COFs), are ideal platforms for hosting radicals while suppressing their self‐coupled annihilation. Yet, current strategies for introducing persistent radicals into these frameworks involve the benzannulation of sterically bulky alkyne‐rich motifs and post‐synthetic addition to alkyne moieties, which in turn compromise the porosity and crystallinity of the frameworks. Herein, a simple backfolded alkyne‐rich diamine‐terminated linker was designed and allowed to form a stable 2D COF, BF‐COF . Upon facile thermocyclisation, radical‐rich BF‐COF‐300 was obtained with retained crystallinity and porosity as well as far intense and wider light absorption than the primitive BF‐COF . These also feature BF‐COF‐300 as a better candidate than BF‐COF in both photothermal conversion and photocatalytic thioether oxidation.