Nonlinear absorption in organometallic materials

We report results of two ongoing investigations that seek to characterize the photophysics of organometallic complexes under one- and two-photon excitation. In the first line of investigation we explore the properties of the triplet state in a complex that contains four individual platinum-acetylide chromophores linked via a tetraphenylmethane unit. Although the individual platinum-acetylide chromophores are not conjugated in the tetramer, transient absorption studies provide clear evidence that triplet-triplet annihilation is very efficient when the complex is excited by sequential two-photon absorption. In a second line of study we have carried out preliminary photophysical studies of an Ir(III) complex that contains a highly conjugated organic ligand that is designed to exhibit a large two-photon absorption cross section. One photon excitation of the Ir(III) complex in the visible region produces a long-lived triplet state that absorbs strongly in the visible and near-infrared regions. Preliminary experiments suggest that the long-lived triplet can be efficiently produced via two-photon absorption in the near-infrared region.