Highly Fluorescent Polyimide Covalent Organic Nanosheets as Sensing Probes for the Detection of 2,4,6-Trinitrophenol

A new fluorescent polyimide covalent organic framework (PI-COF) has been successfully synthesized through solvothermal route using tetra(4-aminophenyl) porphyrin and perylenetracarboxylic dianhydride, which possesses porous crystalline and excellent thermal stability (>500 °C). Furthermore, few-layered PI covalent organic nanosheets (PI-CONs) can be easily obtained from the fluorescent PI-COF through a facile liquid phase exfoliation approach, which were confirmed by atomic force microscopy and transmission electron microscopy analysis. It is interesting that the fluorescent intensity of PI-CONs is obviously enhanced relative to that of PI-COF. The PI-CONs have been successfully utilized as an efficient fluorescent probe for the highly sensitive and selective detection of 2,4,6-trinitrophenol (TNP). The mechanism might be attributed to the combination of electron transfer and inner filter effect based on DFT calculations and spectral overlap data. The system exhibits a good linear response toward TNP over the range from 0.5 to 10 μM with a detection limit of 0.25 μM.