| Abstract
| - A new chemosensor molecule 1 based on a ferrocene-imidazophenanthrolinedyad, effectively recognizes aqueous hydrogenpyrophosphate and theorganic anions ADP and ATP through three different channels. A cathodicshift of the ferrocene/ferrocenium oxidation wave (ΔE1/2 ranging from −130 mV for hydrogenpyrophosphateand fluoride to −40 mV for ADP). A progressive red-shift ofthe absorption bands and/or appearance of a new low energy band at314−319 nm. These changes in the absorption spectra are accompaniedby color changes from pale yellow to orange or pink, which allow thepotential for “naked eye” detection. The emission spectrum(λexc = 390 nm) undergoes an important chelation-enhancedfluorescence effect (CHEF = 50) in the presence of 2.5 equiv of hydrogenpyrophosphateanion and with a large excess of fluoride anion (CHEF = 114). Interestingly,the emission spectrum obtained at different excitation energy (λexc = 340 nm) in the presence of AcOH acid is red-shifted andnot only perturbed by the hydrogenpyrophosphate anion (CHEF = 71)but also with the organic anions ATP (CHEF = 25), ADP (CHEF = 15),and the dihydrogenphosphate (CHEF = 25). The stable heterobimetallicruthenium (II) complex 2 selectively senses the chlorideanion over other anions examined through two channels: cathodic redoxshift (ΔE1/2 = −80 mV) ofthe Fe(II)/Fe(III) redox couple keeping the oxidation wave of theruthenium (II) center unchanged and a significant red emission enhancement(CHEF = 30). 1H and 31P NMR studies as wellas DFT calculations have been carried out to get information aboutwhich molecular sites are involved in bonding. About the deprotonation/coordinationdualism, the combined electrochemical, absorption, emission, and NMRdata strongly support that fluoride anion induces only deprotonation,anions dihydrogenphosphate, ATP, and ADP from hydrogen-bonded complexesand formation of hydrogen-bonded complex between receptor 1 and hydrogenpyrophosphate anion and deprotonation proceed simultaneously.In regards to receptor 2, all available data (electrochemical,absorption, emission, and 1H NMR) strongly support the formation ofa [2·Cl-] hydrogen-bonded complex.
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