The thermal gravimetric analysis (TGA) of JUC-557 showed only 4% weight loss up to 400 ºC, indicating a good thermal stability (Supplementary Fig. ). Furthermore, JUC-557 was inspected by immersing in different organic solvents, boiling water, and strong acid/base (12 M HCl and 14 M NaOH aqueous solutions) for three days or by UV irradiation for 3 h, and unchanged PXRD patterns were observed, manifesting the high chemical stability of sp 2 carbon-linked COFs (Fig. and Supplementary Fig. ).