N-(3-Imidazolyl)propyl dansylamide as a selective Hg2+ sensor in aqueous media through electron transfer

• A highly Hg2+ selective chemosensor 1 was synthesized and investigated.
• N-(3-Imidazolyl)propyl dansylamide acting as a selective Hg2+ sensor in aqueous media.
• The sensor showed high selectivity for Hg+2 even in the presence of other interfering metals (Ag+, Cu+2, Zn+2).
• The detecting mechanism of Hg2+ was based on the electron transfer (ET).

N-Imidazolylpropyl dansylamide 1 was synthesized for the sensing of metal ions and found to be selective and sensitive toward Hg2+ ions in a PBS–EtOH (1:4, pH = 7.4) solution. The sensing ability of probe 1 was examined by UV–Vis, fluorescence, and 1H NMR spectroscopy. The sensing of Hg2+ exhibited a quenching of emission band at λmax = 515 nm of probe 1, which was associated with quenching of green fluorescence emission under 365 nm illumination. Probe 1 showed a good association constant with Hg2+ (Ka = 6.48 × 104 M−1) with a stoichiometry of 1:1 in PBS–EtOH (1:4, pH = 7.4) having the lowest detection limit of 1 μM for Hg2+; on the other hand, probe 2, which has no imidazole moiety, was not able to detect any metal ion. In the case of probe 1, electrons on the imidazole nitrogen are available for electron transfer (ET), which was responsible for its green emission band that was quenched on addition of Hg2+; this clearly indicates that these electrons were used for the formation of a coordinate bond with Hg2+ and that ET was switched off.

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