A preorganized tetradentate phenanthroline-derived amide ligand, N,N'-diethyl-N,N'-ditolyl-2,9-dicarboxamide-1,10-phenanthroline (Et-Tol-DAPhen), was found to show high selectivity towards small copper ions, which might be due to the change of the coordination mechanism from tetradentate to terdentate mode.