COF-1 was synthesized in accordance with the literature report by Côté and coworkers. A Pyrex tube (1.6 cm outer diameter, 1.4 cm inner diameter) was filled with 1,4-benzene diboronic acid (50 mg, 0.30 mmol), followed by 4 mL solvent mixture of 1,4-dioxane: mesitylene (1:1 v/v) and 2 µL of deionized water. The suspension was then sonicated for 30 min. Next the Pyrex tube was flash frozen at 77 K in liquid N 2 and evacuated to 3 x 10 -2 mbar before flame-sealing it (length after sealing: 14.8 cm long). The sample was left to react in an oven at 120 • C for 4 days, yielding a white precipitate which was rinsed by filtration through a frit with acetone (30 mL) before activation by CO 2 supercritical drying.