A novel hydroxyl-containing polyimide as a colorimetric and ratiometric chemosensor for the reversible detection of fluoride ions

A novel hydroxyl-containing polyimide (PI-OH) has been successfully synthesized and subsequently used as a new colorimetric and ratiometric chemosensor for the detection of F⁻ with high selectivity and a fast response time. The ratiometric absorbance changes of the chemosensor PI-OH in DMSO solution show a linear response to F⁻ in the concentration range of 0–0.50 mM with a detection limit of 1.79 μM, which provides a quantitative method for F⁻ detection. ¹H NMR titration and DFT calculation studies confirm the F⁻ sensing mechanism involves H-bond interactions and subsequent deprotonation in the chemosensor. Moreover, the chemosensor PI-OH in DMSO solution can be reversed many times and applied to the visual detection of F⁻. Finally, PI-OH film has been fabricated for real-time visualization of F⁻ with high selectivity and sensitivity. The F⁻ bonded to the PI-OH film can be easily removed by immersing it in acidic solution to recover the sensing ability to F⁻. X-ray photoelectron spectroscopy and energy dispersive spectroscopy analysis indicate that hydroxyl groups in the PI-OH film can bond to F⁻ and the bonded F⁻ can be removed quantitatively. This work provides not only a novel PI film-based sensor device for the visual and reversible detection of F⁻ with high-efficiency, but also a promising F⁻ extractor.