APTES derived polymer with naphthalimide pendant for the fluorescent sensing of picric acid

A fluorescent polymer based on silane was synthesised through the functionalization of 4-bromo-1,8-naphthalic anhydride with Aminopropyltriethoxysilane (APTES), followed by polycondensation (referred to as NI@SiP). Subsequently, substitution at the fourth position with <i>N</i>,<i>N</i>-dimethyl ethylene diamine, led to significant enhancement in the weak fluorescence of the NI@SiP, resulting in the polymer, FNI@SiP. Characterization of the polymer material was conducted using FTIR, FESEM, UV-vis, and fluorescent spectroscopy. FNI@SiP displayed improved solubility along with solvent-dependent fluorescence behaviour. Functionalization at the fourth position of the naphthalimide ring enhanced the fluorescence properties of the material, yielding a quantum yield of approximately 23%. The material exhibited quantitative response towards Picric acid (2,4,6-trinitrophenol denoted as TNP) at micromolar levels by fluorescence quenching in the range 1.7 × 10^-6 M to 2.7 × 10^-4 M, with a limit of detection value 2.63 × 10^-8 M, in aqueous media. The quenching mechanism was further elucidated through time-resolved fluorescence decay measurement, revealing a mixed mechanism involved. Furthermore, a thin film polymer sensor was fabricated, leveraging the silane functionality within the polymer, enabling detection of nitroaromatics, thereby presenting new opportunities for practical application.