A series of potential nonlinear optical (NLO) compounds, (-OH) and (-Cl) substituted derivatives of salicylaldimine-based ligands 1-6 (Fig. 2), was designed and synthesized. Compounds 1 and 2 were characterized by X-ray diffraction analysis, elemental analysis, IR, 1H-NMR, 13C-NMR and UV-Visible spectroscopies. The electric dipole moments (μ) and the first hyperpolarizabilities (β) of the compounds 1-6 were calculated using ab-initio quantum calculations (finite field Møller Plesset perturbation theory). The calculation results reveal that the substituent positions play a significant role in NLO properties of these compounds. © 2004 Elsevier B.V. All rights reserved.