Toward Luminescence Vapochromism of Tetranuclear AuI-CuI Clusters

A family of triphosphine gold-copper dusters bearing aliphatic and hydroxyaliphatic alkynyl ligands of general formula [HC(PPh2)(3)Au3Cu(C2R)(3)](+) (R = cyclohexyl (1), cyclopentyl (2), Bu-t (3), cyclohexanolyl (4), cyclopentanolyl (5), 2,6-dimethylheptanolyl (6), 2-methylbutanolyl (7), diphenylmethanolyl (8)) was synthesized via a self-assembly protocol, which involves treatment of the (AuC2R)(n) acetylides with the (PPh2)(3)CH ligand in the presence of Cu+ ions and NEt3. Addition of Cl- or Br- anions to complex 8 results in coordination of the halides to the copper atoms to give neutral HC(PPh2)(3)Au(3)CuHal(C2COHPh2)(3) derivatives (Hal = Cl (9), Br (10)). The title compounds were characterized by NMR and ESI-MS spectroscopy, and the structures of 1, 4, 7, and 8 were determined by single-crystal X-ray diffraction analysis. The photophysical behavior of all of the complexes has been studied to reveal moderate to weak phosphorescence in solution and intense emission in the solid state with a maximum quantum yield of 80%. Exposure of the solvent-free X-ray amorphous samples 8-10 (R = diphenylmethanolyl) to vapors of the polar solvents (methanol, THF, acetone) switches luminescence with a visible hypsochromic shift of emission of 50-70 nm. The vapochromism observed is tentatively ascribed to the formation of a structurally ordered phase upon absorption of organic molecules by the amorphous solids.