Anion receptors with viologen molecular scaffold

We have designed and synthesized new anion receptors 12+ and 22+. These receptors interact with anions through hydrogen bonds and charge transfer complex depending on the basicity of anion. Therefore, anions with weak basicity such as chloride, bromide, and hydrogen sulfate bound to the receptors 12+ and 22+ only through hydrogen bonds while anions with strong basicity such as fluoride, acetate and dihydrogen phosphate bound to the receptors 12+ and 22+ only through charge transfer interactions at UV–vis titration condition (20 μM). However, in more concentrated 1H NMR titration condition (2 mM), 12+ and 22+ decomposed to form the product one of their amide arm is eliminated. As charge transfer complexes showed colorimetric response, they turned out to be efficient naked eye detector for anions with strong basicity such as fluoride, acetate, and dihydrogen phosphate.