A fluorescence turn-on probe for high SNR monitoring of Mg2+ ions based on Salen-type Schiff base: Synthesis, characterisation and DFT/TD-DFT studies

• Published in: Journal of molecular structure 2025-02, Vol.1321, p.140098, Article 140098
• Main Authors: Zhang, Siman, Huang, Meifen, Jiao, Liang, Weng, Zhehui, Yang, Qiuling, Liao, Nichan, Xu, Qiong, Li, Xiangying, Wu, Qiong
• Format: Article
• Language: English
• Subjects: Fluorescent probe; High signal-to-noise ratio; Magnesium(II) ion detection; Schiff base; Theoretical studies
• ISSN: 0022-2860
• DOI: 10.1016/j.molstruc.2024.140098

•A new Schiff base fluorescent probe with signal-to-noise ratio (SNR) for Mg2+ ion detection.•A molecular probe featuring an exceptionally low detection limitation.•Excellent stability and anti-interference properties for practical applications.•ICT and CHEF effects lead to enhanced fluorescence emission of 6Br-Salmen+Mg2+.•The detection mechanism is validated by experimental and theoretical studies. In this study, a new halogenated Schiff base fluorescent probe, [N, N′-bis(6-bromosalicylidene) ethylene-1,2-diaminopropane] (6Br-Salmen), was synthesized by mixing the equivalent amounts of 6‑bromo-2-hydroxybenzaldehyde and 1,2-diaminopropane precursors in methanol. The structure was characterized through FT-IR, ¹H NMR, and X-ray single-crystal diffraction. The fluorogenic performance demonstrated that although 6Br-Salmen exhibited weak intrinsic fluorescence, its intensity significantly increased by 56.2-fold at 480 nm upon the addition of Mg2+ ions, with a detection limit as low as 5.84 × 10–6 μM. Moreover, the probe showed excellent stability and anti-interference properties, with fluorescence intensity unaffected by external interfering substances. UV titration and ¹H NMR suggested a possible binding mode between Mg2+ and 6Br-Salmen. Theoretical calculations indicated that the enhanced fluorescence emission was mainly due to increased intramolecular charge transfer (ICT) and chelation-enhanced fluorescence (CHEF) effects through coordination of the lone electron pair on the imine nitrogen atom with Mg2+ ions. [Display omitted]