Platinum Acetylide Two-Photon Chromophores (Postprint)

To explore the photophysics of platinum acetylide chromopores having strong two-photon absorption cross-sections, we have investigated the synthesis and spectroscopic characterization of a series of platinum acetylide complexes that feature highly pi-conjugated ligands substituted with pi-donor or -acceptor moieties. The molecules (numbered 1-4) considered in the present work are NLO-functionalized analogs of bis(phenylethynyl)bis(bributylphosphine)platinum(II) complexes. Molecule 1 carries two benzothiazolylfluorene and molecule 2 carries two diphenylaminofluorene substituents bound to the central platinum atom. Compounds 3 and 4 possess two dihexylaminophenyl substituents at their ends and differ by the number of platinum atoms in the oligomer "core" (one vs. two in 3 and 4, respectively). The conjugated ligands impart the complexes with effective two-photon absorption cross sections, while the heavy metal platinum centers give rise to efficient intersystem crossing to afford long lived triplet states. Photophysical studies demonstrate that one-photon excitation of the chromophores produces and S1 state that is delocalized across the two conjugated ligands, with weak (excitonic) coupling through the platinum center(s). The S1 state is observed by ultrafast transient absorption and by its characteristic fluorescence. Intersystem crossing occurs rapidly (k sub isc) approx. 1011/s)) to produce the T(sub 1) state, which is believed to be localized on a single conjugated fluorenyl ligand. The triplet state is strongly absorbing (epsilon (sub TT) > 50,000/M/cm)) and it is very long-lived (tau > 100 microsecs). Femtosecond pulses were used to characterize the two-photon absorption properties of the complexes, and all of the chromophores are relatively efficient two photon absorbers in the visible and near-infrared region of the spectrum (600 - 800 nm).
Pub. in Inorganic Chemistry, v46 n16, p6483-6494, 2007.