Ferrocenyl Compound as a Multiresponsive Calcium Chemosensor with Remarkable Fluorescence Properties in CH3CN

Abstract

We have synthesized a novel disubstituted ferrocenyl compound [Fe(C5H4CO(CH=CH)2C6H4NEt2)2] (3) that displays a remarkable fluorescence quantum yield (1.1 x 10(-1)) in acetonitrile, and we have studied its capacity for calcium detection in depth using both electrochemical and optical techniques in this medium. The results of our NMR analysis reveal that the ligand-calcium interaction is CO-centered and that an uncommon equilibrium occurs between 3 and calcium triflate, involving five species of different stoichiometries. In contrast, our analysis of the UV-vis absorption data indicates that only three species of different stoichiometries are formed when calcium perchlorate is used with 3. Mass spectrometry measurements provide strong support for the formation of all these different species in solution. In addition, the electrochemical detection of calcium triflate by 3 leads to an irreversible Fe(II)/Fe(III) oxidation process with an unusual negative shift (-60 mV) caused by the (n)Bu4NBF4 salt effect on the Ca2+-3 interaction process. Compound 3 can also be an original optical probe to detect calcium perchlorate over a wide range of salt concentration by UV-vis absorption spectroscopy. The most original and intriguing property of compound 3 is that it exhibits an unprecedented "multistep" fluorescence behavior upon addition of this salt.