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

The reactions between the diphosphino-alkynyl gold complexes (XC(6)H(4)C(2)Au)PR(2)-C(6)H(4)-PR(2)(AuC(2)C(6)H(4)X) with Cu(+) lead to the formation of a family of heterometallic clusters of the general formula [{Au(3)Cu(2)(C(2)C(6)H(4)X)(6)}-Au(3)(PR(2)C(6)H(4)PR(2))(3)][PF(6)](2) (X = NO(2), H, OMe, NMe(2); R = C(6)H(5), NC(4)H(4)). These complexes adopt the same structural pattern and consist of a heterometallic alkynyl cluster [Au(3)Cu(2)(C(2)C(6)H(4)X)(6)](-) "wrapped" by the cationic [Au(3)(PR(2)C(6)H(4)PR(2))(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.