Sterically hindered phenolic azomethine dyes derived from aliphatic amines: solvatochromism, DFT studies and antioxidant activity.

Displaying versatile biological activity, Schiff bases are known to possess prominent optical, thermal, and metal coordination properties, rendering them prospective for the design of dyes, photonic devices, ion sensors, molecular probes, etc. Furthermore, azomethine compounds bearing a phenolic moiety may exert antioxidant action. In this work, the antioxidant activity of the bis-substituted and mono-substituted phenolic azomethine dyes derived from 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde was determined in DPPH radical and ABTS cation radical scavenging assays, FRAP and CUPRAC metal reducing assays, and ferrous iron chelating activity assay. The effects of aliphatic amine substituents, steric factors, and the coordination behavior of the compounds on their antioxidant activity were studied. Experimental results of the antioxidant activity assays and plausible mechanisms of antioxidant action were elucidated with reference to the reaction parameters and global reactivity descriptors calculated for the DFT-optimized compound structures. The studied phenolic Schiff bases were characterized by spectroscopic and quantum chemical methods. Solvatochromic properties of the compounds were investigated in terms of the influence of solvent nature and the acidity and basicity of the medium on their catechol imine/quinone methide tautomerism.