A Reflection of literature reports on Synthesis, Spectral Studies, Multilateral applications of Azo dyes

The review article focuses on azo compounds, which contain one or more azo (–N=N–) bonds, and are an important class of synthetic colorants widely used in various industries. This review provides detailed information on the synthesis of azo dyes, including the traditional diazotization–coupling reaction and newer green chemistry methods such as microwave-assisted techniques, sonochemical synthetic routes, and solvent-free techniques, which help reduce environmental pollution and improve efficiency. Various analytical techniques such as ultraviolet–visible (UV–Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, electron spin resonance (ESR) spectroscopy, mass spectrometry (MS), X-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TGA/DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and chromatography are discussed for the structural and functional characterization of azo dyes and their metal complexes. The applications of these dyes in advanced textiles, coatings, electronics and optoelectronics, photovoltaic sensitizers, medicinal and biomedical fields are explained in detail. Special attention is given to the role of azo sensitizers in photovoltaic applications, particularly in dye-sensitized solar cells (DSSC), as well as their significant role in medicinal and biomedical fields, including drug development, targeted therapies, and diagnostic applications. While azo dyes are highly beneficial in many fields, their environmental impact has led researchers to develop safer and more sustainable synthesis methods. This article connects past and recent studies and highlights future possibilities for improving azo dyes for greener and high-performance applications. • This review summarizes classifications, synthesis strategies, and spectral characterization of azo dyes and derivatives, referencing over 100 publications from the past decade. • Covers conventional diazotization–coupling methods and greener approaches including microwave-assisted, sonochemical, solvent-free, clay-catalyzed, and clean syntheses. • Discusses physicochemical properties of azo dyes such as tautomerism, azo–hydrazone equilibrium, photoisomerization (cis–trans switching), solvatochromism, and acid/base responsiveness. • Characterization techniques (UV–Vis, IR, NMR, ESR, MS, XRD, SEM/TEM, TGA-DTA, chromatography, DFT) are reviewed for structure confirmation. • Applications include colorants (indicators, coatings, advanced textiles), material science (catalysis, electronics, photovoltaics), and medicinal/biomedical uses (anti-cancer, antimicrobial agents). • Highlights challenges, opportunities, and future prospects for advancing azo dye research