New mono azo dyes 5-amino-4-[4-(dimethylamino)phenyl]diazenyll-pyrazol-3-ol (A) and 5-amino-4[4-(dimethylamino)phenyl]diazenyl]-2-phenyl-pyrazol-3-one (B) are synthesized and their FT-IR, H-1 NMR and UV-Vis properties are measured. Computational quantum chemistry simulations based on Density Functional Theory (DFT) and Hartree-Fock (HF) by utilizing the basis set of 6-31G(d) are carried out to investigate the molecular structure and some spectroscopic properties, such as FT-IR, H-1 NMR,C-13 NMR and UV-Vis spectra and the frontier molecular orbitals of Compounds A and B. Potential energy distribution (PED) is used to determine the FT-IR vibrational modes of the mono azo compounds. The correlations between the measured and calculated vibrational frequencies are found to be in good agreement with each other. UV-Vis spectrum in different solvents are measured and supported by their ab-initio calculations. The frontier molecular analysis are considered to get the electronic properties of two molecules. A good agreement between the experiment and computation results indicates that DFT and HF methods are able to provide satisfactory results for structural, spectroscopic and electronic properties of mono azo dyes. (C) 2018 Elsevier B.V. All rights reserved.