The electronic absorption spectra, the molecular static first hyperpolarizabilities and the macroscopic nonlinear optical coefficients of the pentanuclear planar “open” transition metal clusters, MoS₄Cu₄(py)₆X₂ (X＝Br, I), have been studied by using the time-dependent density functional theory (TDDFT) at B3LYP/LanL2DZ level. The absorption peaks are red shifted to the experimental data and the first hyperpolarizabilities are enhanced by the substitu-tion of Br by I. The analyses of the low-lying excited states reveal that the charge transfer from 4p/5p orbi-tals of halide center to hybrid orbitals of MoS₄ can contribute most the NLO responses. The charge transfer inside MoS₄ can make contribution as well. The results are helpful to under-stand the relationships between charge transfer and optical excitation, and to the design of novel or-ganic-inorganic hybrid nonlinear optical materials.

Key words: time-dependent density functional theory, transition metal cluster, electronic absorption spectra, second-order nonlinear optical property