Novel 'Turn-Off' and 'Turn-On' Fluorescent Responses for Zr⁴⁺ Enabled by Rare-Earth Coordination Polymers Based on the 2,5-Dihydroxyterephthalic Acid ligand

Two novel isostructural coordination polymers, [[Tb₂(H₂dhtp)(2) (H₄dhtp = 2,5-dihydroxyterephthalic acid), were synthesized via solvent evaporation and thoroughly characterized. Fluorescence studies revealed that both compounds exhibit significant quenching upon exposure to Fe³⁺. Notably, they display a unique and concentration-dependent dual-response to Zr⁴⁺ ions, characterized by distinct fluorescence turn-off (0-1.0 mL for 1; 0-0.9 mL for 2) and turn-on (1.0-7.0 mL for 1; 0.9-5.0 mL for 2) regions. To our knowledge, these materials represent the first examples of Zr⁴⁺-sensing probes based on Tb³⁺/Y³⁺ coordination complexes with the H₄dhtp ligand, showcasing significant potential for the design of novel switchable sensors.