Cd(II)-Based Coordination Polymer as a Multiresponsive Fluorescent Sensor for Efficiently Detecting Zn²⁺, Cr₂O₇^2-, and Phenylglyoxylic Acid

The concentration of Zn²⁺ is closely related to the ecological environment and physical health and must be monitored conveniently and accurately. Herein, a novel coordination polymer, namely, {[Cd₂L₂(bpy)₂]·H₂O·0.25DMF}_n (CP-1, bpy = 2,2′-bipyridine, H₂L = 5-(1H-1,2,4-triazole-1-yl)-1,3-phthalic acid) was synthesized under solvothermal conditions and can be used for selective detection of Zn²⁺ with an extremely low detection limit. Single-crystal X-ray diffraction analyses revealed that CP-1 exhibits an interspersed two-dimensional (2D) layer and further constitutes a 3D layer by weak interactions. Fluorescence experiments showed that CP-1 can be used as an excellent fluorescent sensor for selectively detecting Zn²⁺ with the detection limit as low as 0.073 μM. In addition, CP-1 can also be used for the efficient detection of Cr₂O₇^2- and phenylglyoxylic acid (PGA) with detection limits of 0.68 and 1.59 μM respectively. Moreover, the mechanism study showed that the turn-on behavior of CP-1 for detecting Zn²⁺ can be attributed to absorbance-induced enhancement (ACE), and the turn-off behavior for detecting Cr₂O₇^2- and PGA can be attributed to the “internal filtering effect” (IFE) and the combined effect of photoinduced electron transfer (PET) and competitive absorption, respectively.