Signs alteration of nonlinear refraction of cubane-like shaped clusters from nanosecond to picosecond pulses

The excited-state nonlinear refraction of a novel cubane-like shaped metal cluster MoOS₃ICu₃(2-Mepy)₃ in DMF solution is studied by using Z-scan measurement technique with laser pulses of 10 ns and 40 ps pulse width at the wavelength of 532 nm, respectively. For picosecond pulses the compound possesses a self-focusing property, the positive nonlinear refraction is attributed to population transitions among singlet states, while for nanosecond pulses it exhibits a self-defocusing property and the negative nonlinear refraction is attributed to population relaxing to triplet states.