A novel HBI-based ratiometric fluorescent probe for rapid detection of trifluoroborate

A 2-(2'-hydroxyphenyl)benzimidazole (HBI)-based ratiometric fluorescent probe, known as BTEP, was synthesized using 5-bromosalicylaldehyde as the raw material via Sonogashira coupling and condensation reaction. This probe was designed for rapid detection of boron trifluoride solutions and gases. The N and O coordination atoms in the probe undergo a boron difluoride addition with BF₃, which affects the process of excited state intramolecular proton transfer (ESIPT) leading to a blue shift of fluorescence emission. Obvious changes in the fluorescence signal can be observed within 60 seconds. The introduction of an acetylene trimethylsilane fragment increases the conjugate plane and is beneficial to improving the selectivity of the probe. The I₄₀₈/I₄₇₉ fluorescence ratio of the probe displays a linear relationship with the concentration of BF₃ in the range of 5-50 μM, with a detection of limit as low as 69.5 nM. Furthermore, the probe demonstrates specific and selective recognition of BF₃ among eight common interference substances. Test strips prepared using BTEP have the capability of real-time naked-eye detection of trace BF₃ gas.