An organic NLO single crystal, 4-acetylpyridine fumaric acid (4APFA), was synthesized at room temperature using the slow evaporation method, and single crystal XRD analysis confirmed that the grown crystal is triclinic with a centrosymmetric space group P \(\overline{1 }\) . Using the density functional theory (DFT) approach, experimental results were correlated with theoretical values. The presence of hydrogen bonding interactions that stabilize the molecular structure was understood through NBO analysis. HOMO–LUMO analysis predicts the higher stability and reactivity of the molecule. The major factor contributing to overall crystal packing arises from O–H interactions (39.4%) due to the presence of N–H…O hydrogen bonding interactions. FT-IR and FT-Raman spectroscopy were used to identify different functional groups present in 4-acetyl pyridine fumaric acid. UV-visible spectral analysis of 4APFA shows high optical transmittance throughout the visible region. The material’s blue-band emission was identified through fluorescence spectral analysis. TG/DTA investigation revealed that 4APFA is thermally stable up to 160 °C. The grown 4APFA crystal exhibits excellent atomic packing and good mechanical stability, making it suitable for device fabrication. The higher third-order susceptibility of 4.526 × 10–6 esu and a nonlinear refractive index value of 4.24 × 10–9 cm2/W indicate that the grown 4APFA crystal demonstrates superior NLO behavior, making it highly promising for the design and manufacturing of optical power-limiting devices.
