A novel Schiff base sensor through "off-on-off" fluorescence behavior for sequentially monitoring Al³⁺ and Cu²⁺

A novel Schiff base probe N'-(2-hydroxybenzylidene)-5-(naphthalen-1-yl)oxazole-4-carbohydrazide (G1) was designed and prepared based on a condensation of 5-(naphthalen-1-yl)oxazole-4-carbohydrazide with salicy-laldehyde. G1 gave out a bright blue luminescence in the introduction of Al3+ with an ideal selectivity and sensitivity, which could be acted as a fluorescence "turn-on " probe toward Al3+. The resulted complex G1-Al3+ could be applied to be a quenching probe for Cu2+. The complex stoichiometry of G1 with Al3+ and Cu2+ was confirmed to be 1: 2, via Job's Plot, mass spectrometry titration and theoretical calculation. Moreover, G1 had been successfully applied for monitoring target metal ions in real water sample.