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

A new series of asymmetric salicylaldiminato Schiff base ligands 1-9 has be en synthesized and their structures, electronic properties and second-order nonlinearities are investigated. Three ligands of 1, 4 and 9 with differen t substituents were chosen as models for a theoretical investigation. Geome tric parameters of model ligands and corresponding monoanions suggest that the substituents R-1 and R-2 have no significant effects on complex formati on. The AM1 calculated changes in the bandgap indicate that the overall tre nd of variation of this parameter as a function of increase in the degree o f 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 R-1 and R-2 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-or der nonlinear optical (NLO) property. Although both R-1 and R-2 have effect s on second harmonic generation (SHG) response, but R-2 plays a major role in designing of the NLO salicylaldiminiato Schiff base ligands. (C) 1999 El sevier Science B.V. All rights reserved.