A theoretical investigation of the structure, electronic properties and second-order nonlinearity of some azo Schiff base ligands and their monoanions

Abstract

A new series of asymmetric salicylaldiminato Schiff base ligands 1–9 has been synthesized and their structures, electronic properties and second-order nonlinearities are investigated. Three ligands of 1, 4 and 9 with different substituents were chosen as models for a theoretical investigation. Geometric parameters of model ligands and corresponding monoanions suggest that the substituents R1 and R2 have no significant effects on complex formation. The AM1 calculated changes in the bandgap indicate that the overall trend of variation of this parameter as a function of increase in the degree of nonplanarity is a red-to-blue transition. The analysis of low-electronic transitions of monoanions indicates that the MO more likely to combine with first-row transition metal orbitals is a orbital which is located on the O(2) atom. The Mulliken populations reveal that the influence of the R1 and R2 substituents on the population of the coordination sites is negligible. The molecular hyperpolarizability value of model ligands 1, 4, and 9 were calculated using field finite method. The ligand 1 showed a good second-order nonlinear optical (NLO) property. Although both R1 and R2 have effects on second harmonic generation (SHG) response, but R2 plays a major role in designing of the NLO salicylaldiminiato Schiff base ligands.