An Analysis of the Electronic Absorption Spectrum of Disperse Orange 3—An Azo Dye

In this article, the electronic UV–visible absorption spectra of disperse orange 3 (C₁₂H₁₀N₄O₂) are examined in ethanol solvent at varying concentrations (10⁻³ M, 10⁻⁴ M, 10⁻⁵ M, 10⁻⁶ M, 20 µM, and 40 µM). Azo chromophores are used extensively in the liquid crystal industry, inkjet printing, light-controlled polymers, textiles, and pharmaceutical sectors. The molar extinction coefficient (ε_max) and oscillator strength (f) corresponding to maximum absorbance λ_max (443 nm) in ethanol at concentration 10⁻⁴ M were calculated as 1.35 × 10⁴ M⁻¹ cm⁻¹ and 15.83 × 10⁻² M⁻¹ cm⁻², respectively. The dipole moment of the considered peak was calculated as 4.45 D. Other spectral parameters of scientific importance, such as absorption cross-section and attenuation length, were also calculated as 0.32 × 10⁻¹⁶ cm² and 0.027 cm, respectively. The transitions associated with absorption bands observed at 227 nm, 275 nm, and 443 nm were correlated to (primary π* ← π), (secondary π* ← π), and (π* ← n) by comparison of dye moieties. This confirmed that 10⁻⁴ M is the optimum concentration for spectroscopically investigating the dye (DO3). The quenching was observed by examining fluorescence spectra at various concentrations. The molecule being investigated unequivocally demonstrates fluorescence at 532 nm at 10⁻⁴ M concentration when excited with λ_ex = 440 nm. This results in a notable Stokes shift (Δλ = 89 nm or Δν = 3776 cm⁻¹), which is vital for fluorescence imaging.