A DFT and MP2 study of luminescence of gold(I) complexes

Four Au(I) mixed thiolate and phosphine complexes were studied using DFT, TD-DFT, and MP2/CIS approaches. Two are mononuclear species, [(R3P)Au(p-SC6H4CH3)] differing by the phosphine (PMe3, 1, or PH3, 1h), to check the use of PH3 in the model. The others were binuclear complexes with bidentate phosphines, bridging two gold atoms, modelled by [Au2(p-SC6H4CH3)2{H2P(CH2)nPH2}] (n = 1, 2, 2h and 3h, respectively), to assess the role of the carbon chain in the optical properties. Both DFT and MP2 led to comparable descriptions of the geometry and the electronic structure in the mononuclear complexes, although gold has a stronger participation (and phosphorus a weaker one) in the MP2 virtual orbitals. TD-DFT and CIS give a good reproduction of the electronic absorption, the low-energy excitations being assigned as LMCT [S(p), aryl ring → Au(p)], but CIS leads to a better emission wavelength. The two models, 2h and 3h, used to study the binuclear complexes were found to have similar geometries with comparable Au⋯Au distances, according to DFT calculations. The agreement between calculated and experimental (related complexes) electronic transitions was relatively good, the red shift experimentally observed in 2h relative to 3h being also reproduced by TD-DFT. The low energy transitions were assigned to LMCT [S(p), aryl ring → Au(p)] with mixture of LMMCT, from S(p) to Au–Au dpσ.