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Ferrocene-Based Heteroditopic Receptors Displaying High Selectivity toward Lead and Mercury Metal Cations through Different Channels

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journal contribution
posted on 04.02.2011, 00:00 by María Alfonso, Alberto Tárraga, Pedro Molina
The synthesis and electrochemical, optical, and ion-sensing properties of ferrocene−imidazophenazine dyads are presented. Dyad 4 behaves as a highly selective chemosensor molecule for Pb2+ cations in CH3−CN/H2O (9:1). The emission spectrum (λexc = 317 nm) undergoes an important chelation-enhanced fluorescence effect (CHEF = 47) in the presence of Pb2+ cations, a new low-energy band appeared at 502 nm, in its UV/vis spectrun, and the oxidation redox peak is anodically shifted (ΔE1/2 = 230 mV). The presence of Hg2+ cations also induced a perturbation of the redox potencial although in less extension than those found with Pb2+ cations. Dyad 7, bearing two fused pyridine rings, has shown its ability for sensing Hg2+ cations selectively through three channels: electrochemical, optical, and fluorescent; the oxidation redox peak is anodically shifted (ΔE1/2 = 200 mV), a new low-energy band of the absorption spectrum appeared at 485 nm, and the emission spectrum (λexc = 340 nm) is red-shifted by 32 nm accompanied by a remarkable chelation-enhanced fluorescent effect (CHEF = 165). Linear sweep voltammetry revealed that Cu2+ cations induced oxidation of the ferrocene unit in both dyads. 1H NMR studies have been carried out to obtain information about the molecular sites which are involved in the binding process.