Luminescent μ-ethynediyl and μ-butadiynediyl binuclear gold(I) complexes:: Observation of 3(ππ*) emissions from bridging Cn2- units

The synthesis and X-ray structural and spectroscopic characterization for LAuC drop CAuL . CHCl3 and LAuC dropC-C drop CAuL . 2CH(2)Cl(2) (1 . 4CHCl(3) and 2 . 2CH(2)Cl(2), respectively; L = PCy3, tricyclohexylphosphine) are reported. The bridging C-n(2-) units are structurally characterized as acetylene or diacetylene units, with C dropC distances of 1.19(1) and 1,199(8) Angstrom for 1 . 4CHCl(3) and 2 . 2CH(2)Cl(2), respectively. An important consequence of bonding to Au(I) for the C,,2- moieties is that the lowest-energy electronic excited states, which are essentially acetylenic (3)(pi pi*) in nature, acquire sufficient allowedness via Au spin-orbit coupling to appear prominently in both electronic absorption and emission spectra. The origin lines for both complexes are well-defined and are observed at 331 and 413 nm for 1 and 2, respectively. Sharp vibronic progressions corresponding to nu (C dropC) are observed in both emission and absorption spectra. The acetylenic (3)(pi pi*) excited state of 2 has a long lifetime (tau (0) = 10.8 mus) in dichloromethane at room temperature and is a powerful reductant (E degrees [Au-2(+)/Au-2*] less than or equal to -1.85 V vs SSCE).