Anion‐Dependent Switching: Dynamically Controlling the Conformation of Hydrogen‐Bonded Diphenylacetylenes

With a grain of salt: An anion-dependent switch based on an intramolecularly H-bonded diphenylacetylene is reported. The addition of Cl− causes the conformation of the H-bond acceptor to switch from the urea protons to the amide proton (see scheme; blue N, red O, green Cl), suggesting the use of such systems as fluorescent anion sensors.