Allosteric Fluoride Anion Recognition by a Doubly Strapped Porphyrin

Fluoride fills cavities and insulates polymers: A doubly strapped porphyrin has been designed that is a highly specific receptor for fluoride ions (see picture, yellow: sulfur, red: oxygen, blue: nitrogen, and light blue: fluoride). The strap defines a small cavity about the porphyrin core, and fluoride ion was observed to bind with cooperative allosterism. Larger anions did not bind in the cavity or interfere with fluoride binding. The straps are composed of bis(dithienyl)phenyl groups that can be electropolymerized to give conducting polymers. Exposure of these polymers to fluoride ions results in a dramatic irreversible reduction in conductivity.