DFT Study on Second-order Nonlinear Optical Properties of a Series of Three-dimensional Cobalt(II) Metal Complexes

For designing three-dimensional cobalt(II) metal complexes and Schiff base ligands, the geometry was taken from the starting structures based on the crystallographic data. The density functional theory (DFT) B3LYP/6-31g(d)-FF method was used to calculate the second-order nonlinear optical (NLO) properties of open-shell cobalt(II) metal complexes. The key findings revealed that when compared with the Schiff base ligands, the second-order NLO properties of the metal complexes did not change obviously. The reason is that the NLO responses of cobalt(II) metal complexes are strongly related to intraligand charge transfer processes. According to the frontier molecular orbitals, the less contributions of Co2+ in determining the NLO responses of metal complexes arise from the action of bridging moiety in the charge transfer (CT) processes.