A double responsive fluorescent platform for sensing heavy metal ions based on a dual-emitting fluorescent covalent organic framework hydrogel film

A new luminescent hybrid material with dual-emission centers (Eu@Dye@TpDq hydrogel) based on a covalent organic framework (COF) has been successfully prepared. First, we designed a dye (coumarin) modified COF (TpDq) hybrid fluorescent material (Dye@TpDq), and then the material was formed into a hydrogel film, with an Eu3+ ion being introduced as another luminescent center into the material during the cross-linking process. As a dual-emission fluorescent platform, it exhibits a double-response towards different heavy metal ions: a ratiometric identification response to Cu(II), and a turn-off fluorescence response to Cr(VI). This research not only introduces a novel synthesis of Eu3+-functionalized double emitting COF-based hydrogels, but also inspires the development of COF-based multifunctional analytical tools.