Colorimetric chemical sensing properties of 3-amino-4-hydroxybenzenesulfonic acid-based Schiff bases containing electron donor–acceptor groups

A new series of aminobenzene sulfonic acid-based Schiff bases (1–3) were synthesized from the reaction of 3-amino-4-hydroxybenzenesulfonic acid with 5-methyl, 5-nitro and 5-bromo-salicylaldehyde. The colorimetric and UV–Vis spectroscopic responses of compounds in DMSO to addition of equivalent number of anions (F⁻, Br⁻, I⁻, CN^–, SCN⁻, ClO₄⁻, HSO₄⁻, AcO⁻, H₂PO₄⁻, N₃^– and OH^–) were investigated. Additionally, biological activities of the compounds; antimicrobial and DNA binding properties, were investigated. A DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) free radical method was used to measure antioxidant activity, and 4-hydroxy-3-(2-hydroxy-5-methylbenzylideneamino)benzene sulfonic acid (1) displayed greater antioxidant activity than butylated hydroxytoluene (BHT). Studied compounds demonstrated emission properties over a wide range of visible spectrum, and compound 4-hydroxy-3-(2-hydroxy-5-nitrobenzylideneamino)benzenesulfonic acid (2) has hypsochromic shift by incorporating NO₂ in comparison with other compounds. Femtosecond transient absorption spectroscopy measurements showed that compounds 4-hydroxy-3-(2-hydroxy-5-nitrobenzylideneamino)benzenesulfonic acid (2) and 3-(5-bromo-2-hydroxybenzylideneamino)-4-hydroxybenzenesulfonic acid (3), incorporated nitro and bromine groups and possessing electron accepting features have fast triplet transition. This study provides a novel design strategy for biological activity and colorimetric probing features of aminobenzene sulfonic acid-based Schiff bases.