A multi-cation responsive Ni(ii)-supramolecular metallogel mimics a molecular keypad lock via reversible fluorescence switching

Schiff base HL forms stable Ni( ii )-gel MG (differ from Ni( ii )-complex 1) with triethylamine that serves as reversible ON–OFF–ON fluorescent probe for Zn 2+ /Cu 2+ /Hg 2+ and as sequence dependent molecular keypad lock to protect secret information.