Water-soluble triazole-based azo-Schiff base fluorescent-colorimetric dual chemosensor for selective detection of...

A triazole-based azo-Schiff base ligand (L) has been designed and synthesized as a dual-mode fluorescent-colorimetric chemosensor for the selective and sensitive detection of sulfide ions (S^2-) in aqueous media. The probe exhibits a distinct color change from light yellow to deep orange and a significant fluorescence enhancement upon interaction with S^2-, enabling both naked-eye detection and spectroscopic monitoring. UV-vis titration studies revealed a red shift from 346 nm to 403 nm, while fluorescence emission was enhanced up to 21-fold at 428 nm. The sensing mechanism is not governed solely by basicity-induced deprotonation. The selective response toward S^2- may arise from its higher polarizability, stronger nucleophilicity, and favorable host-guest interaction with the phenolic-azomethine framework of the receptor, supported by ¹H NMR, FTIR, and DFT analyses. The sensor demonstrates high selectivity over competing anions, excellent anti-interference capability, rapid response time, and a low detection limit (3.3 × 10^-7 M). Job's plot confirms a 2 : 1 binding stoichiometry with a strong association constant (5.0 × 10⁵ M^-1). The probe operates effectively over a wide pH range and exhibits reversible sensing behavior in the presence of Hg²⁺ ions, enabling molecular logic gate applications. Practical applicability was validated through successful detection of sulfide ions in spiked water samples with high recovery. Additionally, molecular docking studies revealed strong binding affinity of L with VEGFR-2 (-9.4 kcal mol^-1), indicating potential biological relevance. The ligand also exhibited significant antimicrobial activity, particularly against Gram-negative bacteria, as confirmed by resazurin-based MIC assays. These results highlight L as a multifunctional platform for environmental monitoring, biological sensing, and antimicrobial applications.