Imidazolium-based macrocycles as multisignaling chemosensors for anions.

A series of structurally novel anion receptors 3, 4, and 5 in which a ferrocene unit and a fluorescent moiety are linked to two imidazolium rings have been designed and prepared from 1,1′-bis(imidazolylmethyl)ferrocene. Their crystal structures revealed that these receptors are capable of incorporating anions such as PF6− and Br−. Consequently, the anion binding studies were carried out using various techniques including electrochemistry (CV and OSWV), fluorescence, UV-vis, and 1H NMR spectroscopy. All the receptors showed a special electrochemical response to the F− anion with a remarkable cathodic shift of more than 260 mV and displayed a unique selectivity for F− and AcO− anions with fluorescence enhancement over various other anions of present interest (Cl−, Br−, I−, HSO4−, H2PO4−). In addition, for receptor 5, obvious absorption changes were observed when the H2PO4− anion was added while other anions (F−, Cl−, Br−, I−, AcO−, HSO4−) showed only a minor influence on the UV-vis spectra. 1H NMR titrations demonstrated that receptors 3 and 4 can bind anions through (C–H)+⋯X− hydrogen bonds and showed strong affinity and high selectivity for the AcO− anion in acetonitrile. [ABSTRACT FROM AUTHOR]