A coumarin based “turn-on” type fluorescent probe for the detection of Cu2+ with mechanochromic property

This study presents the design and synthesis of a novel fluorescent probe, (Z)-N'-[[7-(diethylamino)-2-oxo-2H-chromen-4-yl]methylene]-2-hydroxybenzohydrazide (FS). FS demonstrated a pronounced "turn on" type cyan fluorescence upon the addition of Cu²⁺ in a DMSO/PBS solution (1 mM, pH = 7.4, V: V = 1:1). The detection of Cu²⁺ by FS displayed high selectivity, strong anti-interference capabilities, and a low detection limit of 2.46 × 10^–8 M. The binding ratio of FS to Cu²⁺ was determined to be 1:1 according to the Job's plot and DFT calculation while the binding constant was calculated to be 6.20 × 10⁴ M⁻¹. Additionally, the recognition mechanism of FS for Cu²⁺was further elucidated through ESI-MS and ¹H NMR titration analyses. Moreover, FS exhibited mechanochromic property, transforming from yellow to orange fluorescence upon grinding, with the emission wavelength shifting from 551 nm to 597 nm. Meanwhile, the original state could be restored through fumigation with ethanol vapor, and this process was repeatable. Furthermore, FS demonstrated potential applications for Cu²⁺ detection and in the production of pressure-sensitive writing fluorescent display materials.