A highly selective and sensitive colorimetric chemosensor for Fe2+ based on fluoran dye

A highly selective chemosensor based on fluoran dye for Fe2+, 2′-anilino-3′-methyl-6′-dibuthylamino-N-((2′-(2″-ethylimino) methyl) naphthalen-2-ol) iso-indolin-1-one-fluoran (5), was designed and synthesized. The chemical structures of all the intermediates and the fluoran dye 5 are characterized by 1H NMR, 13C NMR, Ms and elemental analysis. Upon addition of Fe2+, the fluoran dye 5 shows a new peak around 658 nm in its absorption spectra, and the color of solution changed from colorless to greenish black. Whereas other ions including Mg2+, Pb2+, Ni2+, Hg2+, Cd2+, Fe3+, Cu2+, Zn2+ and Al3+ and so on induced basically no spectral change, which constituted a Fe2+ highly sensitive and selective colorimetric chemosensor by “naked eyes”.