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, C(48)H(40)FeO(2)N(6) (3) and C(52)H(40)FeO(2)N(6) (4), and the ferrocene-pyrene conjugates, C(29)H(25)FeON(3) (5) and C(31)H(25)FeON(3) (6), have been documented. All the compounds 3-6 behave as very selective redox, chromogenic, and "turn-on" fluorescent probes for Pb(2+) ion in an aqueous environment (CH(3)CN/H(2)O, 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 Pb(2+) ion over other competitor cations such as Hg(2+) and Cd(2+). These chemosensors present immense brightness and fluorescence enhancement (chelation-enhanced fluorescence = 85 for 3 and 92 for 4) following Pb(2+) 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 Pb(2+) ion in aqueous environment over Hg(2+) and Cd(2+) cations. All the compounds have been characterized by (1)H, (13)C 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.