Crystalline Dioxin-Linked Covalent Organic Frameworks\nfrom Irreversible Reactions

Abstract

Triangular\n2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and linear\ntetrafluorophthalonitrile (TFPN) or 2,3,5,6-tetrafluoro-4-pyridinecarbonitrile\n(TFPC) were linked by 1,4-dioxin linkages to form crystalline 2D covalent\norganic frameworks, termed COF-316 and -318. Unlike the condensation\nreactions commonly used to crystallize the great majority of COFs,\nthe reactions used in this report are based on nucleophilic aromatic\nsubstitution reactions (S_NAr) that are considered irreversible.\nOur studies show that the reactivity of TFPN and TFPC with HHTP is\nenhanced by the nitrile substituents leading to facile reactions of\nplanar building units to yield the present 1,4-dioxin linked COFs.\nBecause these reactions are irreversible, the resultant frameworks\nhave high chemical stability in both acid and base. This has led to\npostsynthetic modifications of COF-316 by reactions necessitating\nextreme conditions to covalently install functionalities not otherwise\naccessible. We also report the permanent porosity of these COFs.