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

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