A low-toxic strontium-based coordination polymer for highly sensitive and selective fluorescent detection of carbonate ions via dynamic quenching

Luminescent coordination polymers (CPs) have attracted considerable interest for carbonate detection owing to their high sensitivity and selectivity. However, their practical application is often limited by the low abundance and high toxicity of commonly used metal ions such as Cd²⁺, Cr²⁺, and Eu³⁺. Here, a new Sr-CP, [Sr(H₂QA)₂]_n (CP-1) {H₃QA = (E)-5-((8-hydroxyquinolin-5-yl)diazenyl)isophthalic}, was successfully synthesized under hydrothermal conditions using low-toxic Sr²⁺ ions and an azo-based dicarboxylic acid ligand (H₃QA). The obtained compound demonstrates excellent thermal stability and maintains structural integrity in various organic solvents and aqueous environments. It exhibits a highly sensitive turn-off fluorescence response toward CO₃²⁻ in aqueous solution, along with remarkable anti-interference ability against other common ions, achieving a K_SV of 1.524 × 10⁴ M⁻¹ and an LOD of 9.92 × 10⁻⁶ M. The fluorescence quenching of CP-1 induced by CO₃²⁻ is mainly attributed to a dynamic quenching mechanism driven by structural reorganization.