Aldazine-based colorimetric sensors for Cu 2+ and Fe 3+

Abstract

We have developed novel aldazine-based colorimetric chemosensors for Cu 2+ and Fe 3+. 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 Cu 2+ over the other alkali and transition metal ions. In the presence of Cu 2+, 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 Fe 3+ over alkali and transition metal ions. In the presence of Fe 3+, 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 Cu 2+ and Fe 3+, respectively. However, the quenched fluorescence of JA–Fe 3+ complex can be reversibly restored using cysteine.