Luminescent Mononuclear Ag(I)−Bis(diphosphine) Complexes: Correlation between the Photophysics and the Structures of Mononuclear Ag(I)−Bis(diphosphine) Complexes

Correlation between the photophysics and the structures of three Ag(I)−bis(diphosphine) complexes ([Ag(dppbz)2]NO3 (1·NO3), [Ag(dppe)2]NO3 (2·NO3), and [Ag(dppp)2]NO3 (3·NO3) (dppbz = 1,2-bis(diphenylphosphino)benzene, dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,3-bis(diphenylphosphino)propane) has been investigated using temperature-dependent emission measurements and electrochemical and theoretical methods. All three Ag(I)−bis(diphosphine) complexes have relatively low oxidation potential, which allows metal-to-ligand charge transfer (MLCT) contribution in the lowest excited state of the tetrahedral geometry, which is difficult in other Ag(I) complexes. Both 1·NO3 and 2·NO3 show orange phosphorescence with moderate quantum yield in air-free methanol at room temperature, while 3·NO3 is less emissive in solution at room temperature. In all three complexes the temperature-dependent luminescence measurements in EtOH/MeOH 4:1 (v/v) solution indicate the blue-shift of the emission maximum and the increase of the emission intensity on lowering the temperature. In particular, the sequential emission spectral change with decreasing temperature is observed in 1·NO3 and 2·NO3. In the glass state at 90 K, all three complexes show intense blue phosphorescence. The theoretical calculation using density functional theory (DFT) suggests that the orange and blue emissions mainly originate from the 3MC excited state based on a square-planar geometry and the 3IL+3MLCT excited state based on a tetrahedral geometry, respectively.