Solid-state 13C and 15N NMR experiments were conducted on a Bruker AV-500 (500 MHz) or a Bruker Avance NEO 400 (400 MHz) spectrometer at 297–300 K. All samples were fully activated, packed, and sealed in zirconia rotors in an argon-filled glovebox before loading into the probe for measurements. Experiments on AV-500 spectrometer were performed using a Bruker 4-mm double resonance MAS probe (1H/X) operating at 125.75 MHz for 13C and at 50.69 MHz for 15N, and a magic angle spinning rate of 8 kHz. Experiments on the NEO 400 spectrometer were performed using a 3.2-mm or 1.3-mm MAS probe (1H/X) operating at 100.65 MHz for 13C and at 50.69 MHz for 15N, and a magic angle spinning rate of 24 kHz. The magic angle was calibrated by maximizing the number and intensity of rotational echoes for the 79Br resonance for KBr under MAS. 13C chemical shifts were externally referenced to the downfield resonance of adamantane at 38.48 ppm. 15N chemical shifts were externally referenced to glycine at 33.4 ppm. 13C multiple cross-polarization (multi-CP) experiments were performed using the compensated-multi-CP (compMulti-CP) sequence developed by Schmidt Rohr and coworkers. The data were read and processed with MestReNova such as polynominal background substraction for integration.

We report the first covalent incorporation of reactive aliphatic amine species into covalent organic frameworks (COFs). This was achieved through the crystallization of an imine-linked COF, termed COF-609-Im, followed by conversion of its imine linkage to base-stable tetrahydroquinoline linkage through aza-Diels-Alder cycloaddition, and finally, the covalent incorporation of tris(3-aminopropyl)amine into the framework. The obtained COF-609 exhibits a 1360-fold increase in CO2 uptake capacity compared to the pristine framework and a further 29% enhancement in the presence of humidity. We confirmed the chemistry of framework conversion and corroborated the enhanced CO2 uptake phenomenon with and without humidity through isotope-labeled Fourier transform infrared spectroscopy and solid-state nuclear magnetic resonance spectroscopy. With this study, we established a new synthetic strategy to access a class of chemisorbents characterized by high affinity to CO2 in dilute sources, such as the air.

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