Abstarct: In this thesis, have been attended to bis(salicylidene aniline) zinc(II) [Zn(saa)2] complex, which is a complex of schiff baxses. This complex is used mainly in organic light-emitting diodes (OLEDs). the molecular geometry and vibrational frequencies of [Zn(saa)2] complex have been calculated by density functional theory (DFT) methods (B3LYP) using three basis sets 6-31G** and 6-311G** and LANL2DZ. The results of the optimized molecular structure are compared with the experimental X-ray structure. The optimized geometric parameters are described well by the 6-311G** basis set at B3LYP level. Vibrational frequencies were assigned and compared with the experimental values. The results indicate the difference between the observed and scaled wave number values is small. Then the influence of p-substituents in the aniline ring of [Zn(saa)2] complex on structure parameters and spectra properties related to ligand bonds to Zn (II) are studied at B3LYP/6-311G**. These substituents include electron donating electron withdrawing groups such as -CH3, -OCH3, -CN, NO2 and -N(CH3)2 groups. The research demonstrated that the electronegativity of the different substitution groups on the Schiff-baxse ligand can finely tune spectroscopic properties of the corresponding Zn complexes. The sequence of the electron donating ability of substitution groups -N(CH3)2> OCH3> CH3> H> CN> NO2 is in accordance with the height of the LUMO levels, increasing vibration frequencies of Zn-N, increasing red shift in UV-VIS spectrum. Following these changes, the performance of each of the complexes in OLEDs was different.