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 Cr2O72– 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 Cr2O72– and PGA can be attributed to the “internal filtering effect” (IFE) and the combined effect of photoinduced electron transfer (PET) and competitive absorption, respectively.