Alkynyl-Protected Au₂₂(C≡CR)₁₈ Clusters Featuring New Interfacial Motifs and R-Dependent Photoluminescence

A series of homoleptic alkynyl-protected gold clusters Au₂₂(C≡CR)₁₈ were newly synthesized using 3-ethynylthiophene (ETP-H), phenylacetylene (PA-H), 3-ethynyltoluene (ET-H), and 3-ethynylanisole (EA-H). Single-crystal X-ray diffraction analysis on Au₂₂(ETP)₁₈ revealed that a bitetrahedral Au₇ core is protected by novel Au₃(ETP)₄ oligomers and a Au₆(ETP)₆ ring, composed of R-C≡C-Au(I)-C≡C-R units bridged by π-Au-π bonds. UV-visible and ¹H NMR spectroscopy revealed that the R groups did not affect the geometric and electronic structures of Au₂₂(C≡CR)₁₈, whereas the photoluminescence quantum yield was dependent on the R group and showed the highest value of 4.6% when R = Ph.