A covalent organic polymer for turn-on fluorescence sensing of hydrazine

Abstract

It is very important to detect hydrazine sensitively, efficiently, and selectively since hydrazine is a highly toxic organic molecule which will bring great threat to the health of human beings. Herein, a covalent organic polymer, COP-Ta, containing ynone reaction sites has been designed and successfully synthesized via the Sonogashira coupling reaction by using tetrakis(4-ethynylphenyl)ethene (TPE-Al) and terephthaloyl chloride (TPC). COP-Ta exhibits weak fluorescence in the solid state and uniform dispersion of ethanol. But when hydrazine is added into the uniform dispersion of ethanol, the fluorescence of the dispersion is significantly enhanced due to the chemical reaction between the ynone structure in COP-Ta and hydrazine, in which the ynone structure cyclizes to pyrazole, leading to the restriction of the intramolecular charge transfer effect, and the obvious increase of fluorescence from COP-Ta. As a turn-on fluorescence sensor for the detection of hydrazine, COP-Ta shows a high sensitivity (detection limit: 0.16 μM), a wide linear range (0–50 μM), and a high selectivity. COP-Ta can detect hydrazine under weakly acidic, neutral, and weakly alkaline conditions in aqueous solutions. In addition, COP-Ta has been applied to detect hydrazine in real water samples. More importantly, we have successfully applied this sensor for the detection of hydrazine in human blood serum, and achieved satisfactory detection performance. This demonstrates that the fluorescent covalent organic polymer containing the ynone structure can be used for the detection of hydrazine effectively and applied in the field of environmental protection.