Pyridoxal Derived AIEgen for Fluorescence Turn-off Sensing of Cu2+ and Fe2+ Ions and Fluorescence Imaging of Latent Fingerprints

Schiff base 4-((E)-((E)-(2-hydroxybenzylidene)hydrazono)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol ( HSP) was synthesized by condensing vitamin B 6 cofactor pyridoxal with salicylaldehyde hydrazone, and characterized by standard spectroscopic techniques (FT-IR, 1 H NMR, 13 C NMR, and ESI–MS). The solution of HSP in DMSO/HEPES (10 mM, pH = 7.4) mixed solvents with varying HEPES fractions ( f w ) from 0 to 95% showed aggregation-induced emission (AIE). The AIE active HSP in 95% HEPES gave intense fluorescent emission at 570 nm was employed for the detection of metal ions. The fluorescence of HSP was quenched upon adding Cu 2+ and Fe 2+ ions. The association constant ( K a ) of the Schiff base HSP with Cu 2+ and Fe 2+ ions was estimated as 4.08 × 10 5 M −1 and 1.23 × 10 5 M −1 , respectively by using the online analysis tool BindFit v0.5. The HSP showed the detection limit down to 1.75 µM and 1.89 µM for Cu 2+ and Fe 2+ ions, respectively. Further, the aggregates of HSP were applied to visualize latent fingerprints (LFPs) over a non-porous glass slide.