Rational Design\nof Regenerable Amino-Functionalized\nFluorescent Covalent Organic Framework for the Exclusive Detection\nof Mercury(II)

Goal-oriented development of novel\ncovalent organic frameworks\n(COFs) to construct a sensing platform for highly toxic mercury (II,\nHg<sup>2+</sup>) is of tremendous significance. Recently, numerous\nCOFs with sulfur-based ligands were developed for Hg<sup>2+</sup> monitoring;\nhowever, strong binding of Hg<sup>2+</sup> by sulfur makes their regeneration\nvery tough. Herein, we designed and developed an amino-functionalized\nfluorescent COF (COF–NH<sub>2</sub>) through facile postmodification\nfor Hg<sup>2+</sup> detection in which the π-conjugation skeleton\nis the signal reader and the nitrogen-based side is the highly selective\nHg<sup>2+</sup> receptor. More importantly, this nitrogen-based receptor\npermits the reversible binding of Hg<sup>2+</sup>. As a sensing platform,\nthe outstanding performance of COF–NH<sub>2</sub> for Hg<sup>2+</sup> detection was reached with respect to high sensitivity with\nan ultralow detection of 15.3 nM, real-time response with rapid signal\nchange of 10 s, and facile visualization with significant fluorescence\ncolor change. Expectedly, COF–NH<sub>2</sub> obtained facile\nrecycling which still shows excellent response performance toward\nHg<sup>2+</sup> after six cycles based on the reversible interaction\nbetween amino groups and Hg<sup>2+</sup>. Our work not only shows\nan attractive foreground of fluorescent COF for Hg<sup>2+</sup> detection\nbut also emphasizes the easy construction of novel COF materials via\nthe rational introduction of metal ligands for the recognition of\nother metal ions.