<p>A novel azo dye is synthesized by reacting 4-hydroxy-3-methoxybenzoic acid with 4-amino-2,3-dimethyl-1-phenyl-3-pyrazol-5-one (azo dye N₁). The synthesized azo dye N₁ is characterized by Fourier transform infrared (FT-IR), mass, ¹H and ¹³C nuclear magnetic resonance (NMR), and ultraviolet–visible (UV–Vis) spectroscopic techniques and melting point analysis. The B3LYP (Becke, three-parameter, Lee–Yang–Parr)/6-311+G(d,p) basis set is utilized to ascertain the sample geometry by density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. Calculations of the quantum chemical descriptors are carried out to examine the sample's nonlinear optical (NLO) properties. The NLO properties of the sample are investigated under excitation with continuous-wave (CW) laser beams at 473 nm and 532 nm wavelengths. The nonlinear refractive index (NLRI) of the sample is ascertained using the 473 nm CW laser beam to obtain diffraction patterns (DPs) and Z-scan, where NLRI values of 3.698 × 10⁻⁷&#xa0;cm²/W and 0.25 × 10⁻⁷ cm²/W are obtained. We found that the value of the refractive index of the azo dye N₁ calculated by the latter method is greater than its value for other materials. The all-optical switching (AOS) property of the azo dye N₁ is demonstrated when the controlling beam is at 473 nm and the controlled beam is at 532 nm.</p>