A Phenanthroimidazole-based Fluorescent Turn-Off Chemosensor for the Selective Detection of Cu²⁺ in Aqueous Media

A new phenanthroline-based chemosensor 3-(1H-phenanthro[9,10-d]imidazol-2-yl)benzene-1,2-diol (1) was synthesized for the recognition of Cu²⁺. Sensor 1 showed selective fluorescence quenching for Cu²⁺ in aqueous media. Detection limit (0.87 μM) for Cu²⁺ was much lower than WHO guideline (31.5 μM). Sensing property of 1 toward Cu²⁺ was studied by fluorescence and UV–Vis titrations, and Job plot and ESI-MS analyses. Moreover, turn-off fluorescence mechanism of 1 toward Cu²⁺ induced by intramolecular charge-transfer (ICT) and ligand-to-metal charge-transfer (LMCT) was well demonstrated by theoretical calculations.