Highly Specific and Sensitive Naked-Eye Fluoride Ion Recognition via Unzipping a Helical Poly(phenylacetylene)

Abstract

Fluoride anion (F–) recognition has attracted much attention in recent years due to its significant role in biological, medical, environmental, and industrial processes. Although many artificial receptors show high sensitivity toward F–, they still lack the specificity for such an anion. It still remains a great challenge to endow the receptors with high specificity and sensitivity toward F– at the same time. Herein, a contracted cis-cisoid poly(phenylacetylene) derivative (Poly-1) has been synthesized, whose preferred-handed helix can be stabilized by intramolecular hydrogen bonding networks among neighboring pendant amides. The average layer distance between its side chains of 3.88 Å can provide a small pocket, which is suitable to accommodate the smallest anion F– with high basicity, but excludes other anions. When the first F– binds to the pendant amides via intermolecular hydrogen bonding, the main chain conformational transition into a stretched cis-transoid nonpreferred-handed helix is triggered, which facilitates the subsequent F– binding. Such an unzipping effect gives rise to an ultralow detection limit of 2.85 × 10–8 M (0.54 ppb) for F–. Meanwhile, the solution color change from colorless to yellow can be observed because of the conjugated cis-transoid conformation of Poly-1. As a result, a highly specific and sensitive naked-eye recognition toward F– is realized. This work lays a solid foundation for the development of smart materials on the basis of stimuli-responsive cascade processes.