Fluoride Ion Sensing by an Anion−π Interaction

Abstract

We report the discovery of a supramolecular interaction (anion−π and charge/electron transfer, CT/ET) involving fluoride ion and π-electron deficient colorless naphthalene diimide (NDI) receptors. Strong electronic interactions between lone-pair electrons of F⁻ ion and π*-orbitals of the NDI unit lead to an unprecedented F⁻→NDI ET event, which produces an orange colored NDI^•− radical anion. Further reduction of NDI^•− by another F⁻ ion produces a pink colored NDI²⁻ dianion, rendering NDI a colorimetric F⁻ sensor. Preorganization of two NDI units in overlapping positions using folded linkers improves their selectivity and sensitivity for the F⁻ ion significantly, allowing F⁻ detection at nM concentration in 85:15 DMSO/H₂O solutions.