Aims: The development of a sensitive and visual analytical method for detecting and monitoring the change of pH has always attracted great interest because it plays significant role in chemical reactions, environmental monitoring, and biological systems. Methods: In this paper, a simple condensation reaction from readily available substrates 2-hydroxy-1-naphthylaldehyde and malononitrile has been carried out to produce probe L with good aggregation-induced luminescence, and its chemical structure was confirmed by 1H NMR, 13C NMR and ESI-MS. Objective: There is a conjugated system containing electron-withdrawing cyano group and electron-donating hydroxyl group in molecular structure of probe L, and which exhibits obvious fluorescence intensity and visible color change through intramolecular charge transfer (ICT) under different pH conditions. Results: Probe L assumes excellent fluorescence intensity in DMF/H2O (1:9, v:v) mixed solvent system, and exhibits good reversibility in a very narrow range of pH values (pH = 12.5~13), which indicates that it can be used for the analysis and visual detection to pH change in DMF/H2O system. Conclusion: In addition, probe L can also selectively identify solvent DMSO by the induction of fluorescence quenching, which means that probe L may be used as the indicator for the detection and monitoring of trace amount of DMSO.

A novel fluorescent probe L based on benzimidazole derivative for selective CN− detection was designed and synthesized, and its structure was identified by spectral analysis. In DMSO/H2O (v/v=7 : 3, pH=9) solvent system, the fluorescence intensity for L enhances and the color change from yellow to colorless and purple was immediately observed at 426 nm, but there was no obvious color change when other anions instead of CN− was added to the system. The mechanism on CN− recognition was also studied by 1H NMR, IR, MS analysis and theoretical calculations. The probe L for CN− detection exhibited high sensitivity, and the molar ratio and lowest detection limit was 1 : 1 and 8.2×10−7 mol L−1, respectively. In addition, the probe L could be successfully applied to the detection of CN− in bitter almond, and was also used as a test paper, which indicated that the probe L might conveniently carried out the quick identification and detection of cyanide ion in the environment and food samples through its fluorescent color change under UV lamp.