From molecule to complex: Design of smart fluorescent anion-sensors

A novel 2-(2-pyridyl)benzimidazole (a) compound with hydrogen bond unit was synthesized as an anion receptor. It is noteworthy that only fluoride anions can led to its fluorescence change from ultraviolet (362 nm) to visible region (408 nm) compared with AcO−, Cl−, Br−, and I−. Spectroscopic studies demonstrated that the recognition process can be attributed to the hydrogen bonding interactions between F− and the imidazole-NH. More importantly, this ligand can coordinate to europium ion and a novel europium complex Eu(a)3(NO3)3·H2O possessing red emission was prepared. We noted that the luminescence of this complex can be completely quenched by F− as well as AcO−. However, we recognized that the competitive coordination interactions between anions and ligand resulted in the quenching effects.

► A ligand with hydrogen bond moiety was prepared for anion sensing.
► The europium complex can exhibit red emission upon excitation at 335 nm.
► The sensitized emission of the complex can be completely quenched by F− as well as AcO−.