Two Dual-Emission Zn(II)–Tb(III) Coordination Polymers Controlled by Metal–Ligand Ratios for Ratiometric Sensing of Malachite Green

Malachite green (MG) is an effective fungicide, but it is highly toxic, carcinogenic, and bioaccumulative, posing serious risks to food safety, ecological environments, and public health. Therefore, the accurate and sensitive detection of MG is essential. Herein, two ratiometric fluorescent sensors based on two bimetallic Zn(II)-Tb(III) coordination polymers (CPs) were developed for MG detection. The two Zn(II)-Tb(III) CPs were synthesized by controlling metal-ligand ratios, namely, [Zn₂Tb₂(DCA)₁₀(phen)₂] (<b>1</b>) and [Zn(phen)₃][Tb₃(DCA)₁₁] (<b>2</b>) (DCA = 3,5-dichlorobenzoate and phen = 1,10-phenanthroline). They present as two distinct structures with a zero-dimensional (0D) tetranuclear Zn₂Tb₂ cluster structure for <b>1</b> and a 0D + 1D ionic pair structure for <b>2</b>. Both CPs show excellent fluorescence properties with dual-emission and high stability. They can be applied as ratiometric sensors for MG detection with detection limits as 146 and 137 <i>n</i>M for <b>1</b> and <b>2</b>, respectively. Furthermore, the two CPs can also detect MG in real shrimp samples with good recoveries. The sensing mechanism involves the synergistic effects of IFE, FRET, dynamic quenching, and PET. Importantly, the two ratiometric sensors realized portable and visual detection of MG via the smartphone-assisted RGB method, which has great potential for instant detection of MG.