Synthesis, Characterization, and Properties of Binuclear Gold(I) Phosphine Alkynyl Complexes

Reactions of gold salts with various π-conjugated dialkynes have led to two homologous series of binuclear alkynylgold(I) complexes, linear rigid-rod Cy₃PAu−C≡C−(CHCH)_n−C≡C−AuPCy₃ (n = 1−3, all-trans) (2a−c) and photochromic LAu−C≡C−DTE−C≡C−AuL (DTE = 1,2-di(2-methylthien-3-yl)cyclopentene or 1,2-di(2-methylthien-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene) (L = PCy₃, tricyclohexylphosphine or PPh₃, triphenylphosphine) (4a−d). The photophysical properties of these complexes have been investigated. The emission spectra exhibited a progressive red-shift with increasing length of the bridge between the two Au(I) in the linear metal complexes 2. Photochromic alkynylgold(I) complexes 4 also exhibited fluorescence properties, and the emission wavelength was found to change upon variation of the dithienylethene (DTE) linkers as well as of the auxiliary phosphine ligands. It is revealed that the binuclear alkynylgold complexes with DTE units show photochromic behavior and that the efficiencies of the photochromic processes and conversions from the open- to the closed-ring isomers in the photostationary state (PSS) are greatly improved upon the introduction of gold. The photochromic process was also found to show complete reversibility, with restoration of the luminescence and NMR signals upon exposure to visible light.