Sensitive and selective redox, chromogenic, and “turn-on” fluorescent probe for Pb(II) in aqueous environment

Abstract

The electrochemical, optical, and metal cation sensing properties of the triazole-tethered ferrocene–anthracene conjugates, C₄₈H₄₀FeO₂N₆ (3) and C₅₂H₄₀FeO₂N₆ (4), and the ferrocene–pyrene conjugates, C₂₉H₂₅FeON₃ (5) and C₃₁H₂₅FeON₃ (6), have been documented. All the compounds 3–6 behave as very selective redox, chromogenic, and “turn-on” fluorescent probes for Pb²⁺ ion in an aqueous environment (CH₃CN/H₂O, 2/8). The significant changes in their absorption spectra are accompanied by a strong color change from yellow to greenish blue, which allows a prospective use for the “naked eye” detection of Pb²⁺ ion over other competitor cations such as Hg²⁺ and Cd²⁺. These chemosensors present immense brightness and fluorescence enhancement (chelation-enhanced fluorescence = 85 for 3 and 92 for 4) following Pb²⁺ coordination within the limit of detection at 2 ppb. Interestingly, their fluorescence, redox, and colorimetric responses are preserved in presence of water, which can be used for the selective colorimetric detection of Pb²⁺ ion in aqueous environment over Hg²⁺ and Cd²⁺ cations. All the compounds have been characterized by ¹H, ¹³C NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS) spectrometric analysis, and the solid-state structures of 5 and 6 have been unequivocally established by X-ray diffraction analysis.