Density functional theory (DFT) with the BHandHLYP functional was employed to investigate the polarizability and second-order nonlinear optical (NLO) coefficients of C^N^N ligands, C^N^NPt(II) (C^N^N＝6-phenyl-2,2-bipyridines) and N^C^NPt(II) (N^C^N＝1,3-di(2-pyridyl)-benzene) complexes. The calculations indicate that the second-order NLO coefficients of complexes are enhanced significantly and the β value of complex 2b is about 11 times as large as that of ligand Lb. In addition, the second-order NLO coefficients of complexes are also enhanced by increasing the conjugation of ancillary ligands and the electron-withdrawing ability of substituents. The electronic spectra of complexes were analyzed by the time-dependent density function theory (TD-BHandHLYP) method. The results show that the experimental absorption spectra are well reproduced by the theoretical data. The maximum absorptions of C^N^NPt(II) and N^C^NPt(II) complexes are assigned to different kinds of electronic transitions. And the substituents have larger effects on the maximum absorptions of N^C^NPt(II) complexes, while less effects on that of C^N^NPt(II) complexes.

Key words: Pt(II) complex, electronic spectra, second-order NLO coefficients, DFT