Abstract We have synthesized naphthaldehyde–carbonohydrazone (NC) and naphthaldehyde–thiocarbonohydrazone (NTC) Schiff base ligands by the condensation reaction of 2-hydroxy naphthaldehyde with urea and thiourea, respectively. Both these Schiff base ligands show blue turn-on fluorescence in the presence of aluminum (III), as a result of a restricted C= N isomerization mechanism. Aluminum (III) can be detected in the ...