Viologen-based redox-switchable anion-binding receptors

A series of viologen-based receptors have been synthesized and their anion-binding properties have been investigated by-NMR, UV-visible spectroscopy, electrochemistry and X-ray diffraction analyses. Linking two positively charged viologens through a propyl chain promotes a remarkable chelate-like binding of chlorides revealed by 1H-NMR spectroscopy. Of all the anionic species investigated, only fluoride is detectable by the naked eye and by electrochemical methods. The reduction-triggered formation of a π-dimer from two viologen-based cation radicals was also investigated by electrochemical and spectroelectrochemical methods and by theoretical calculations.