A reaction-based approach for fluorescence sensing of fluoride through cyclization of an O-acyl pyrene amidoxime derivative

Abstract

A novel reaction-based O-acyl pyrene amidoxime derivative was easily synthesized from pyrene-1-carbaldehyde in three step and fully characterized. The sensing ability of the receptor towards various anions were investigated. The receptor exhibited distinct fluorescent behavior by a 45-fold increase in the emission intensity upon reacting with fluoride. The fluoride-induced cyclization reaction of the receptor led to formation of a highly fluorescent pyrene 1,2,4-oxadiazole derivative. However, other anions such as Cl−, Br−, I−, AcO−, NO3−, ClO4−, H2PO4− and HSO4− could not exhibit a remarkable increase in emission intensity. The fluorescence quenching of the receptor was explained by photoinduced electron transfer mechanism. The suppressing of photoinduced electron transfer, which was triggered by cyclization reaction between O-acyl amidoxime moiety and fluoride, led to an off-on type blue emission output. Fluoride could be detected with the present receptor up to a lower concentration limit down to 1.36 μM. The fluorescence response of the receptor was rationalized by time-dependent density function theory calculations. Moreover, a practical application showed that the receptor could be exploited as a test paper in the fluorescence detecting for fluoride in water samples.