Synthesis of novel azo linkage-based Schiff bases including anthranilic acid and hexanoic acid moieties: investigation of azo-hydrazone and phenol-keto tautomerism, solvatochromism, and ionochromism

Abstract

Two new azo-Schiff base receptors (L1 and L2) containing azo and azomethine groups with a conjugatedgroup (benzyl ring of anthranilic acid, in L1) and electron-donating group (alkyl chain of hexanoic acid, in L2)were synthesized and characterized. Azo-hydrazone/phenol-keto tautomerism and solvatochromism were investigated. Studying their sensing ability towards cations (Co 2+ , Cu 2+ , Zn 2+ , Ni 2+ , Pb 2+ , Cd 2+ , Mn 2+ , Fe 3+ , Cr 3+ , and Al 3+), high sensitivity and selectivity were recorded for Fe 3+ by naked eye and UV-Vis spectra in DMF-aqueous HEPES buffer (v:v, 1:1, pH 6.8). The color of L1 and L2 solutions instantly changed from yellow to deep orange and pale orange. L2 sensed Cu 2+ and Al 3+ ions selectively by UV-Vis spectra. The interactions of receptors with F − , Cl − , CH3 COO − , C2 O 2−4, H2PO −4, and OH − anions were also investigated in DMF-HEPES 1:1 and 4:1 solvent mixtures. L1 sensitivelyresponded to anions according the order of OH − >C2 O2−4 >F − in the 1:1 mixture and OH − >F − >CH3 COO −>C2 O2−4 in the 4:1 mixture in UV-Vis spectra with color changing from pale yellow to dark yellow. However, L2 showed weak spectral changes in the UV-Vis spectra, so its sensitivity was poorer than L1 , attributed to the effect ofalkyl chains.