One-pot cascade construction of nonsubstituted quinoline-bridged covalent organic frameworks

Abstract

Irreversible locking of imine linkages into stable linkages represents a promising strategy to improve the robustness and functionality of covalent organic frameworks (COFs). We report, for the first time, a multi-component one-pot reaction (OPR) for imine annulation to construct highly stable nonsubstituted quinoline-bridged COFs (NQ-COFs), and that equilibrium regulation of reversible/irreversible cascade reactions by addition of MgSO₄ desiccant is crucial to achieve high conversion efficiency and crystallinity. The higher long-range order and surface area of NQ-COFs synthesized by this OPR than those of the reported two-step post-synthetic modification (PSM) facilitate charge carrier transfer and photogeneration ability of superoxide radicals (O₂˙⁻), which makes these NQ-COFs more efficient photocatalysts for O₂˙⁻ mediated synthesis of 2-benzimidazole derivatives. The general applicability of this synthetic strategy is demonstrated by fabricating 12 other crystalline NQ-COFs with a diversity of topologies and functional groups.