Excited state optical nonlinearity of cubane-like shaped clusters

Nonlinear absorption and refraction of novel cubane-like shaped metal clust ers WOS3Cu3I(2-Mepy)(3) (I) and MoOS3Cu3I(2-Mepy)(3) (II) in DMF solution a re studied by using Z-scan measurement technique with laser pulses of 10 ns pulse-width at the wavelength of 532 nm. The compound (I) possesses a self -focusing property, while compound (II) exhibits a self-defocusing property . The refractive nonlinearity of the cluster can be attributed to the excit ed-state nonlinear refraction effect. A theoretical model of the excited-st ate refraction is presented to analyze the experimental results. The theore tical results are in good agreement with the experimental data. The conditi on of the sign change of nonlinear refraction is also studied. (C) 2000 Els evier Science B.V. All rights reserved.