Synthesis and Spectroscopic Characterization of Azo Dyes Derived From 4-(Dimethylamino) Benzaldehyde: Solvatochromic and Antimicrobial Studies

Abstract

The discharge of synthetic dyes and auxiliary biocides from textile finishing operations constitutes a significant source of aquatic pollution, driving demand for multifunctional colorants that consolidate processing steps and reduce chemical effluent loads. This study reports the aqueous-based synthesis of two azo dyes via diazotisation of 1-aminoanthraquinone and 4-chloroaniline followed by coupling with p-dimethylaminobenzaldehyde, yielding an orange product (Dye 1, 77.0%) and a red product (Dye 2, 87.5%). UV–Visible spectroscopy revealed a positive solvatochromic shift of 11 nm for Dye 1 (λ_max = 469 nm in acetone → 480 nm in DMSO), indicative of intramolecular charge-transfer character with potential utility in environmental polarity sensing, whereas Dye 2 exhibited solvent-independent absorption at 471 nm. FT-IR analysis confirmed the presence of azo, carbonyl, and amino functionalities in both compounds. Antimicrobial evaluation against Staphylococcus aureus, Escherichia coli, and Candida albicans demonstrated that Dye 1 possessed superior activity (MIC = 12.5, 12.5, and 50 mg mL⁻¹, respectively) compared with Dye 2 (MIC = 25, 50, and 100 mg mL⁻¹). The integration of colouring and antimicrobial properties within a single molecular framework offers a viable strategy for eliminating separate biocidal finishing steps, thereby reducing the discharge of persistent and bioaccumulative antimicrobial agents into aquatic ecosystems. Future work should prioritise biodegradability assessment, aquatic ecotoxicity profiling, and life-cycle analysis to establish the full environmental viability of these multifunctional colorants.