Thiourea-based multifunctional fluorescent materials: From metal and anion detection to antibacterial polymer films

Two new dansyl-based thiourea derivatives (L1 and L2) were synthesized and characterized in both the solid state and in solution, including single-crystal X-ray diffraction analysis. Both compounds exhibit pronounced solvatochromic behavior and enhanced fluorescence in aqueous-rich media (90% H₂O; enhancement factor of 60% for L2), consistent with aggregation-induced emission (AIE) characteristics and demonstrating their suitability for operation in predominantly aqueous environments. Notably, substitution of the benzyl ring with electron-withdrawing CF₃ groups in L2 significantly modulates the photophysical properties, leading to altered emission behavior and sensitivity toward analytes. The sensing performance of L1 and L2 toward halide and pseudohalide anions (F^-, CN^-, Cl^-, Br^-) was investigated. Both ligands display selective fluorescence quenching in the presence of fluoride and cyanide, with CN^- producing the most significant response. The limits of detection (LOD) and quantification (LOQ) for CN^- were determined to be 2 and 3.3 μM for L1, and 2.7 and 5.3 μM for L2, respectively, highlighting the impact of electronic substitution on sensing performance. This response was further translated into a colorimetric platform, enabling naked-eye detection of cyanide through the appearance of a pink coloration within the millimolar concentration range. In addition to anion sensing, both compounds were evaluated as probes for metal ions, exhibiting measurable responses toward Hg²⁺ (for L1, LOD = 2.7 μM). Density functional theory (DFT) calculations provided insight into the binding interactions, supporting the proposed coordination mode and relative stability of the complexes. These findings has been confirmed by MS spectra. Furthermore, the compounds display intrinsic antibacterial activity, with L2 showing selective efficacy against Gram-positive bacteria and a minimum inhibitory concentration (MIC) of 3 μg/mL against Staphylococcus aureus. Incorporation into polymeric matrices enabled the extension of this activity to solid-state materials.