Sensitive fluorescent detection of p-nitrobenzene derivatives with electron-donating groups utilizing an F-rich fluorescent covalent organic framework

Nitrobenzene compounds (NBCs) containing electron-donating groups, such as p -nitrobiphenyl (p-NBP), p-nitrophenol (p-NP), and p-nitroaniline (p-NA), exhibit high environmental and biological accumulation and are highly toxic, even at trace concentrations. Given the existence of various NBCs and their respective isomers, the development of sensitive detection method is urgently required. To address this need, a novel fluorine (F)-rich fluorescent covalent organic framework (COF), named COF-LY, was synthesized. COF-LY, featuring superior fluorescence properties based on dual intramolecular charge transfer (ICT) effects, demonstrated good selectivity and sensitivity for p-NBP, p-NA, and p-NP due to differences in interaction sites and forces. Notably, p-NBP, p-NA, and p-NP at a concentration of 0.5 μg·mL −1 were successfully distinguished from a mixture containing 40-fold concentrations of their ortho−/meta-isomers (20 μg·mL −1 ). Furthermore, the detection limits (LODs) for these compounds were determined to be as low as 3.33 ng·mL −1 , which is remarkably satisfactory. The effectiveness of the sensor was validated through analysis of real water, fish, and mung bean sprout samples, yielding recoveries ranging from 81.40 %–114.78 %. This study not only proposed a strategy for enhancing the fluorescence properties of fluorescent COFs by incorporating strongly electron-withdrawing groups but also developed a sensitive detection and distinction method for p-NBP, p-NA, and p-NP. These findings significantly expand the application potential of fluorescent COFs in environmental monitoring, food safety, and other fields. However, it should be noted that the sensors are affected by the concentration of interfering substances (isomers). COF-LY cannot differentiate a mixture of p-NBP, p-NA and p-NP; it can only differentiate one of these compounds from their isomers. Further improvements in sensor performance are needed to address these issues.