Excited State Absorption in Cubane-Like Transition Metal Clusters

We report an investigation of excited-state absorption in cubane-like transition metal clusters. The fluence-dependent transmittances of the clusters have been measured with using 8-ns laser pulses. Time-resolved transmission measurements show that the triplet-triplet absorption occurs within a few nanoseconds. We have also developed a five-level (two singlet states, two triplet states, and one ionized state) model to simulate the excited-state absorption in these cluster compounds. The comparison between the model and the experimental measurements indicates that the population of the triplet states is created mainly by an ionization-recombination process and the triplet-triplet transitions are responsible for the observed nonlinear absorption.