Construction of coordination polymer-based fluorescent sensors for highly selective detection of Al³⁺ and Cr₂O₇²⁻ Ions

Transition metal-based coordination polymers (CPs) have emerged as promising fluorescent materials for environmental sensing due to their structural diversity and functional tunability. In this work, two novel CPs—{[Cu(L)(TBTA)(H₂O)₂]·H₂O}ₙ (CP1) and {[Co(L)(TBTA)]·2H₂O}ₙ (CP2)—were synthesized <i>via</i> solvothermal reactions using a bis-benzimidazole ligand (L) and tetrabromoterephthalic acid (H₂TBTA). Single-crystal X-ray diffraction analysis revealed that CP1 adopts a two-dimensional layered architecture with a typical octahedral Cu²⁺ coordination geometry involving two nitrogen atoms from L, two water molecules, and two oxygen atoms from TBTA. In contrast, CP2 features a distinct interpenetrating 2D network constructed from Co²⁺ centers coordinated by N₂O₂ donor sets and bridged through TBTA ligands, resulting in a zigzag topology. Photoluminescence studies showed that CP1 exhibits an emission peak at 510 nm and displays a selective fluorescence quenching response toward Al³⁺ ions, with a Stern–Volmer quenching constant (Ksv) of 8.51 × 10⁴ M⁻¹ (R² = 0.9851). CP2, on the other hand, demonstrates strong sensitivity toward Cr₂O₇²⁻ with a Ksv value of 4.60 × 10⁴ M⁻¹ (R² = 0.9991). Both CPs exhibited good aqueous dispersibility, signal reproducibility, and fluorescence stability over multiple sensing cycles. These results highlight their potential as structurally distinct, ion-selective fluorescent platforms for the detection of environmentally relevant metal cations and anions.