Synthesis and Second-Order Nonlinear Optical Properties of New Copper(II), Nickel(II), and Zinc(II) Schiff-Base Complexes. Toward a Role of Inorganic Chromophores for Second Harmonic Generation

A new Schiff-base ligand based on the condensation of diaminomaleonitrile and 4-(diethylamino)salicylaldehyde is reported with its copper, nickel, and zinc complexes. Their second-order nonlinear optical properties are investigated by electric field induced second harmonic (EFISH) and ZINDO quantum-chemical calculations to probe the role of the metal center in the nonlinearity. All the complexes exhibit a second-order nonlinear response that is larger than that of the ligand with an hyperpolarizability (β) value of 400 (±100) 10 - 30 cm 5 esu - 1 for the zinc derivative at 1.34 μm. Theoretical calculations indicate that the two-level model is inadequate to describe the nonlinearity in such systems.