Luminescent gold(I) acetylides: From model compounds to polymers

The emission spectra of rigid-rod, conjugated polymeric complexes of gold(I) of the type [-Au-C=C-Ar-C=C-Au-L-L-](x), where Ar = aryl and L-L = diphosphine or bis(isocyanide) ligands are reported for the first time, along with the corresponding spectra of analogous mononuclear and binuclear alkynylgold(I) model complexes. It is found that the emission spectra display a red shift on going from mononuclear to binuclear to polynuclear structures, and it is tentatively argued that this provides evidence for extended pi-conjugation in the polymers. Many of the model complexes display a red shift in the emission spectra on going from solution in dichloromethane to the solid state; in most cases, this is attributed to the presence of intermolecular Au ... Au bonding in the solid state but, in one case, it is also observed when the intermolecular Au ... Au distance is too long to be consistent with a bonding interaction. Assignments of the emission spectra are aided by EHMO (extended Huckel molecular orbital) calculations on model complexes. Structures of the model complexes [Me3P-Au-C=C-C6H2Me2-C=C-Au-PMe3], the first digold diacetylide to be structurally characterized, and [XyN=C-Au-C=C-C6H4-NO2] have been determined crystallographically.