Azomethines containing 1,3,4-oxadiazole ring: Synthesis, photophysical properties, halochromism and metal ions sensing responses

Abstract

New azomethines were synthesized by condensation reactions of salicylaldehyde with various aromatic amines containing 1,3,4-oxadiazole ring. A reference sample without the 1,3,4-oxadiazole ring was prepared using 1,3-bis(4-aminophenoxy)-benzene. The chemical structure was confirmed by FTIR and 1H NMR spectroscopy. The absorption and photoluminescence properties were investigated in tetrahydrofuran, acetonitrile, and N,N-dimethylformamide solutions. The obtained azomethines had absorption bands in the range of 240–420 nm and emitted violet and/or blue light located between 340 and 600 nm. In the DMF solution, one of the samples showed the excitation-wavelength dependent emission properties by shifting from ~ 382 to 442 nm. Furthermore, under basic conditions, the intensity of the main absorption band decreased and a new band appeared (at 420 nm), with a concomitant change of color from colorlessto yellow. Finally, the spectral study of interactions of new azomethines with Cu2+, Co2+, Ag+, Ni2+, Sn2+, Zn2+ and Hg2+ revealed significant spectral changes and selectivity for Zn2+, Cu2+, Co2+ and Ag+ ions.