Multifunctional fluorescent probe selective for Cu(II) and Fe(III) with dual-mode of binding approach

Unsymmetrical azine Schiff base 5-diethylamino-2-[(4-diethylamino-benzylidene)-hydrazonomethyl]-phenol (receptor 1) having multiple binding sites (–NEt2 and –OH group) have been synthesized. The receptor 1 exhibits color change from light yellow to purple and bright yellow in presence of Cu2+ ion and Fe3+ ion, respectively which is detectable by naked-eye. But it shows red color in presence of mixture of all metal ions. The UV–vis spectral investigation of receptor 1 shows a remarkable spectral shift from 410 nm to 527, 572 and 620 nm in presence of Cu2+ ion and 485 nm in presence of Fe3+ ion in acetonitrile solvent. Interestingly, Cu2+ ions generates a new charge transfer emission band at 532 nm in the expense of local emission of receptor at 480 nm, but Fe3+ ion only quenched the local emission. The spectral response of receptor is almost insignificant in presence of other metal ions (Mn2+, Zn2+, Co2+, Ni2+, Cd2+, Hg2+, Li+ and Na+ ions).