Switching Analyte Selectivity via Metal-Node Modulation in Hydroxy-Functionalized Coordination Polymers: Experimental and DFT Studies

Modulation of metal nodes provides a powerful strategy to control excited-state behaviors in coordination polymers (CPs). Herein, we report the synthesis of two hydroxy-functionalized CPs, namely, STCP-1 and STCP-2, constructed from 2,5-dihydroxyterephthalic acid and Zn 2+ or Mg 2+, respectively, for the detection of antibiotic residues. Single-crystal X-ray diffraction (SCXRD) analysis reveals subtle variations in hydroxy coordination that significantly influence the electronic structure and overall photophysical properties. STCP-1 exhibits strong fluorescence in aqueous medium, enabling the detection of dimetridazole with a detection limit of 0.035 ppm and a K sv of 0.11 × 10 6 M –1 . On the contrary, STCP-2 preferentially recognizes larger antibiotics such as doxycycline and tetracycline with detection limits of 0.143 ppm ( K sv = 0.70 × 10 5 M –1 ) and 0.164 ppm ( K sv = 0.18 × 10 5 M –1 ), respectively, within a very short response time (∼5 s). Mechanistic insights from UV–vis, fluorescence, XPS, cyclic voltammetry, and time-correlated single photon counting (TCSPC), corroborated by density functional theory (DFT) analyses, indicate that photoinduced electron transfer (PET) and weak non-covalent interactions govern the sensing process. Furthermore, STCP-1 demonstrates practical applicability in real samples, including river water and food supplements, and enables smartphone-assisted recognition with a detection limit of 2.2 ppm.