Aldazine-based colorimetric sensors for Cu2+ and Fe3+

We have developed novel aldazine-based colorimetric chemosensors for Cu2+ and Fe3+. The aldazine ligands were synthesized by simple condensation of 4-diethylamino-salicylaldehyde and 8-hydroxyjulolidinal with hydrazine. The (4-diethylamino)-salicylaldehyde-azine (SA) showed high selectivity and sensitivity towards Cu2+ over the other alkali and transition metal ions. In the presence of Cu2+, absorption band of SA at 425 nm red shifted to 545 nm. The color of solution changed from pale yellow to purple color. Interestingly, 8-hydroxyjulolidinal-azine (JA) showed selectivity towards Fe3+ over alkali and transition metal ions. In the presence of Fe3+, the color of the ligand solution changed from pale yellow to violet. The absorption band of JA at 445 red shifted to 575 nm. The fluorescence of ligands SA and JA was completely quenched in the presence of Cu2+ and Fe3+, respectively. However, the quenched fluorescence of JA–Fe3+ complex can be reversibly restored using cysteine.