DFT studies on second-order nonlinear optical properties of a series of axially substituted bis(salicylaldiminato) zinc(II) Schiff-base complexes

Abstract

Coordination of an axial ligand to metal center to enhance the second-order nonlinear optical(NLO) response of a two-dimensional bis(salicylaldiminato) zinc(II) Schiff-base complex is an unprecedented model. The second-order NLO responses of a series of axially substituted bis(salicylaldiminato) zinc(II) Schiff-base complexes were explored according to the finite field(FF) method at CAM-B3LYP/6-31+G(d) level(LANL2DZ basis set for metal atoms). The results show that the second-order NLO properties can be effectively tuned by exchanging the donor and accepter of the axial ligand and extending the length of the conjugated bridge along the axial direction. A system involving the electron acceptor along the appropriate direction has a large three-dimensional second-order NLO response. Meanwhile, time dependent density functional theory(TD-DFT) method was employed to calculate the physical parameters of excited states. The results show that the Y- and Z-polarized transitions of the zinc(II) Schiff-base complex are the first and second excited states, respectively, and have a low-lying excited energy. Although the X-polarized transition has a high excited energy, the large oscillator strength indicates that it will significantly contribute to the second-order NLO response.