Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh3)-Au-Ca parts per thousand C}(2)-phen, has been synthesized from Au(PPh3)Cl (PPh3 = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh3)-Au-Ca parts per thousand C}(2)-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed (3) pi-pi* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh3)-Au-Ca parts per thousand C}(2)-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh3)-Au-Ca parts per thousand C}-phen, and 3-ethynylphenanthroline, 3-{(PPh3)-Au-Ca parts per thousand C}-phen was observed. The absorption bands assignable to the pi-pi*(Ca parts per thousand Cphen) transition and phosphorescent emission assignable to the metal-perturbed (3) pi-pi* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.