The flexible EDAN-based covalent organic frameworks constructed by flexible knots and 4,4′-ethylenedianiline as a linker for adsorping and fluorescence sensing iodine

In this paper, 4,4′-ethylenedianiline as a linker, flexible 2,4,6-tris(4-formylphenoxy)- 1,3,5-triazine (TPT − 3 − CHO) and hexa(4-formyl-phenoxy)cyclotriphosphazene (NOP − 6 − CHO) as knots were selected to construct the new flexible EDAN-based COFs (TEDAN and HEDAN) through Schiff base reactions of aldehyde and amine. The as-prepared flexible EDAN-based COFs have high crystallinity, sizable surface area, and thermal stability. With porous properties, abundant electron-rich heteroatoms as well as large π-conjugated network structures that can provide effective binding sites, TEDAN and HEDAN exhibit good reversible vapor-trapped iodine with the adsorption capacities of 4.64 and 2.25 g g −1 , respectively. The aromatic networks of nitrogen-rich units in TEDAN provide many binding sites with guest iodine molecules than that of HEDAN, resulting in higher equilibrium uptake capacity of iodine for TEDAN. In addition, the flexible EDAN-based COFs show “turn-off” detection of non-radioactive iodine in the dispersion state with quenched constants (K SV ) of 5.59 × 10 4 and 2.35 × 10 4  L mol −1 . The fluorescence quenching of the flexible TEDAN-based COFs can be attributed to both the photo-induced electron transfer mechanism and the energy transfer transfer mechanism. The sensitivity of HEDAN is higher than that of TEDAN.