Fluorescence Probes Based on Aminoboranes for the Detection of Fluoride Ions and Nitroaromatics: A Bifunctional Fluorescence Detection Platform

Small-molecule-based fluorescent probes have garnered significant attention because of their excellent optical properties. Among these, multi-stimuli-responsive molecular fluorescent probes have been rapidly developed for their wide range of applications. In this study, we designed a bifunctional fluorescent probe based on three-coordinate boron compounds to detect fluoride ions and 4-nitrophenol. Two compounds NB1 and NB2, containing B-mesityl₂ acceptors (A) and nitrogen-containing aromatic donors (D), were confirmed via single-crystal X-ray diffraction. The donor–acceptor (D–A) structure and substantial steric hindrance enable these compounds to exhibit efficient fluorescence emission in both liquid and solid states. Leveraging the properties of three-coordinate boron, these two compounds exhibit a visible and rapid response to fluoride ions, with detection limits of 0.41 μM for NB1 and 1.31 μM for NB2. The detection mechanism was corroborated by ¹⁹F NMR and fluorescence emission spectra. Moreover, owing to the D–A B–N unit, both compounds exhibit a significant and rapid response to 4-nitrophenol, resulting from interrupted charge transfer. These compounds serve as fluorescent probes with outstanding bifunctionality, stability, and high efficiency. Given the growing demand for multi-stimuli-responsive fluorescent probes, NB1 and NB2 possess great potential for a wide range of future sensing and detection applications.