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

•A novel fluorescence sensor (G1) was designed and synthesized based on 5-(naphthalen-1-yl)oxazole-4-carbohydrazide and salicylaldehyde.•G1 could be acted as an “off-on-off” sensor to sequentially detect Al3+ and Cu2+ with excellent sensitivity and selectivity through different sensing mechanisms.•The optimized structure and energy calculation of G1, G1-Al3+, and G1-Cu2+ were gained by Gaussian09 to demonstrate the binding mechanism.•G1 had been successfully applied for the detection of Al3+ and Cu2+ in real water sample with satisfactory recovery and RSD.