Selective metal ion recognition <i>via</i> positional isomers: fluorescent chalcone-1,2,3-triazole hybrids for Co( <scp>ii</scp> ) and Cu( <scp>ii</scp> ) detection

This study reports the synthesis of three positional isomers (6a-6c) of chalcone-tethered 1,2,3-triazoles <i>via</i> the Cu(i)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. The synthesized probes were comprehensively characterized using FTIR, ¹H and ¹³C NMR, and mass spectrometry. Their potential as metal ion sensors was evaluated through UV-vis and fluorescence spectroscopy, revealing high selectivity and sensitivity toward Co(ii) and Cu(ii) ions. The probes 6a-c exhibited low limits of detection (LoD): 1.64 μM (Co(ii)) and 3.19 μM (Cu(ii)) for ortho isomer (6a), 2.08 μM (Co(ii)) and 2.30 μM (Cu(ii)) for meta substituted (6b), and 1.81 μM (Co(ii)) and 1.17 μM (Cu(ii)) for para-substituted (6c) 1,2,3-triazole derivatives. Job's plot analysis confirmed a 1 : 1 metal-ligand complex formation. To further elucidate binding interactions, Density Functional Theory (DFT) calculations were conducted, employing B3LYP/6-31G+(d,p) for free probes and B3LYP/LANL2DZ for their metal complexes. The combined experimental and theoretical results establish a robust and selective sensing platform for Cu(ii) and Co(ii) detection, with promising applications in environmental monitoring and analytical chemistry.