Simple Bisthiocarbonohydrazones as Sensitive, Selective, Colorimetric, and Switch‐On Fluorescent Chemosensors for Fluoride Anions

Abstract

Bisthiocarbonohydrazones are found to be a class of sensitive, selective, ratiometric, and colorimetric chemosensors for anions such as fluoride (F⁻) or acetate (Ac⁻). The sensitivities, or the binding constants of the sensors with anions, were found to be strongly dependent on the substituents appended on the π-conjugation framework, the delocalization bridge CHN, the aromatic moiety, and the hetero atom in the CX group (X=O, S) of the sensors. Single-crystal structures and ¹H NMR titration analysis shows that the CHN moiety is a hydrogen-bond donor, and it is proposed that an additional CH⋅⋅⋅F hydrogen bond is formed for the sensors in the presence F⁻. A sensor bearing anthracenyl groups is demonstrated as a switch-on fluorescent chemosensor for F⁻ and Ac⁻. The recognition of F⁻ in acetonitrile (MeCN) by a sensor with nitrophenyl substituents is tolerant to MeOH (MeCN/MeOH=10:1, v/v) and water (MeCN/H₂O=30:1, v/v); at these solvent ratios the absorption intensity of the sensor–F⁻ complex solution at maximal absorption wavelength was attenuated to half of the original value in pure MeCN.