Toward Luminescence Vapochromism of Tetranuclear Au^I–Cu^I Clusters

A family of triphosphine gold–copper clusters bearing aliphatic and hydroxyaliphatic alkynyl ligands of general formula [HC­(PPh₂)₃Au₃Cu­(C₂R)₃]⁺ (R = cyclohexyl (<b>1</b>), cyclopentyl (<b>2</b>), Bu^t (<b>3</b>), cyclohexanolyl (<b>4</b>), cyclopentanolyl (<b>5</b>), 2,6-dimethylheptanolyl (<b>6</b>), 2-methylbutanolyl (<b>7</b>), diphenylmethanolyl (<b>8</b>)) was synthesized via a self-assembly protocol, which involves treatment of the (AuC₂R)_<i>n</i> acetylides with the (PPh₂)₃CH ligand in the presence of Cu⁺ ions and NEt₃. Addition of Cl^– or Br^– anions to complex <b>8</b> results in coordination of the halides to the copper atoms to give neutral HC­(PPh₂)₃Au₃CuHal­(C₂COHPh₂)₃ derivatives (Hal = Cl (<b>9</b>), Br (<b>10</b>)). The title compounds were characterized by NMR and ESI-MS spectroscopy, and the structures of <b>1</b>, <b>4</b>, <b>7</b>, and <b>8</b> 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 <b>8</b>–<b>10</b> (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