Synthesis of new luminescent bis-azo-linkage Schiff bases containing aminophenol and its derivative. Part I: Studying of their tautomeric, acidochromic, thermochromic, ionochromic, and photoluminesence properties

In this work, two novel bis-azo-linkage Schiff bases (H4L1 and H4L2) containing conjugated group (phenol ring in H4L1 and nitro-phenol ring in H4L2) were synthesized by using new azo-aldehyde compound AZ-1 (3,3'-(4-nitro-1,2-phenylene)bis(diazene-2,1-diybbis(2-hydroxy-5-nitrobenzaldeyde). They were characterized by elemental analysis and IR, H-1/C-13 NMR, UV-vis, and masss pectral techniques. Prototropic tautomeric equilibrium (azo-imine <-> hydrazone-imine or azo-imine <-> azo-amine), and acido-, thermo-, ionochromism in these Schiff bases were investigated by UV-vis spectroscopy. Photochromism study indicated that DMSO solution of H4L1 and H4L2 exhibits strong green luminescence at room temperature upon photoexcitation, attributed to exist as hydrazone-imine form in the excited state. Emission wavelength was 505 and 523 nm in photoluminescence spectra. On the other hand, azo-imine tautomer was stabilized by increasing of temperature in the ground state in solution for both H4L1 and H4L2. As well, H4L2 showed a selective and sensitive colorimetric sensing toward acid-base and anions (F-, CH3COO-, C2O42- and SO32-).