Multiresponsive Luminescent Sensitivities of a 3D Cd-CP with Visual Turn-on and Ratiometric Sensing toward Al³⁺ and Cr³⁺ as Well as Turn-off Sensing toward Fe³⁺

Abstract

By using the reduced Schiff base tricarboxylate ligand H₃cip, one novel 3D Cd-based coordination polymer (<b>Cd-CP</b>) with the formula [Cd(Hcip)(bpea)_0.5(H₂O)]_<i>n</i> (H₃cip = 5-(3-carboxybenzylamino)isophthalic acid, bpea = 1,2-bis(4-pyridyl)ethane) has been solvothermally synthesized. The prepared <b>Cd-CP</b> possesses a 4-connected CdSO₄ net based on dinuclear {Cd₂} units. Luminescence measurements revealed that the complex exhibited ratiometric turn-on luminescence responses toward Al³⁺ and Cr³⁺ with a significant color change, which could be easily distinguished by the naked eye under ultraviolet light. <b>Cd-CP</b> can also respond to Fe³⁺ through a turn-off mechanism. Interestingly, the luminescence quenched by Fe³⁺@<b>Cd-CP</b> can be recovered and increased significantly by adding some competitive Al³⁺, while Cr³⁺ can only marginally increase the luminescence intensity of Fe³⁺@<b>Cd-CP</b>. Moreover, the detection of the three aforementioned metal ions can be realized by using <b>Cd-CP</b>-coated test papers, extending the potential application regions of the reported material to point-of-care tests and environmental field studies.