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. [ABSTRACT FROM AUTHOR]