ABSTRACT. The azo dye of 1,3-dimethylxanthine, namely 8-[(4-acetyl phenyl azo)]-1,3-dimethylxanthine (APAX), was prepared in two steps. The first step included the formation of the diazonium salt by reacting 4-aminoacetophenone with sodium nitrite NaNO2 under acidic conditions and completing the diazotization process while maintaining a low temperature below 5 °C. The resulting diazonium salt was reacted with the 1,3-dimethylxanthine compound and obtained on the azo dye, which was characterized by UV-Vis, FT-IR, 1H-NMR spectroscopies and elemental analysis. DFT calculations were performed to obtain optimized geometry of the ligand. These calculations were performed using three functionals and 6-311++ G (d,p) basis and allow to determinate bond length, bond angles, dihedral and HOMO and LUMO energies. The APAX ligand exhibited considerable color changes when it mixed with solution of cobalt, copper and zinc ions, therefore, it is considered a probe to detect these ions. Metallic complexes of APAX ligand were prepared by interacting aqueous solutions of the metallic salts of Co(II), Cu(II) and Zn(II) with APAX ligand under a molar ratio equal to 2:1 (APAX ligand : metal). The APAX dye and the complexes showed exciting biological activity against E. coli, Staph. aureus and Aspergillus. The APAX dye was pH sensitive and exhibited interesting photochromic behavior.   KEY WORDS: 1,3-Dimethylxanthine, Dye, Complexes, pH sensitive, Probe, Bacteria, DFT calculations   Bull. Chem. Soc. Ethiop. 2023, 37(2), 347-356.                                                               DOI: https://dx.doi.org/10.4314/bcse.v37i2.8