Intensely Luminescent Alkynyl-Phosphine Gold(I)−Copper(I) Complexes: Synthesis, Characterization, Photophysical, and Computational Studies

The reactions between the diphosphino−alkynyl gold complexes (XC₆H₄C₂Au)PR₂−C₆H₄−PR₂(AuC₂C₆H₄X) with Cu⁺ lead to the formation of a family of heterometallic clusters of the general formula [{Au₃Cu₂(C₂C₆H₄X)₆}Au₃(PR₂C₆H₄PR₂)₃][PF₆]₂ (X = NO₂, H, OMe, NMe₂; R = C₆H₅, NC₄H₄). These complexes adopt the same structural pattern and consist of a heterometallic alkynyl cluster [Au₃Cu₂(C₂C₆H₄X)₆]⁻ “wrapped” by the cationic [Au₃(PR₂C₆H₄PR₂)₃]³⁺ “belt”. The novel compounds were characterized by NMR spectroscopy and ESI-MS measurements. A systematic study of their luminescence properties revealed efficient room-temperature phosphorescence in solution with remarkably weak quenching by molecular oxygen. The photophysical experiments demonstrate that the increase in the electron donor ability of the alkynyl ligands and the electron-withdrawing character of the diphosphines results in the bathochromic shift of emission maxima (in the 576−686 nm range) and a decrease in the luminescence quantum yield. The electronic structure calculations showed that variations of X or R substituents have very little effect on the structural parameters but display a significant influence on the electronic properties of the clusters and characteristics of luminescence. The metal-centered triplet emission within the heterometallic alkynyl cluster is suggested to play a key role in the observed phosphorescence.