Photophysical and Electroluminescent Properties of PtAg₂ Acetylide Complexes Supported with meso- and rac-Tetraphosphine

1,2-Bis­[[(diphenylphosphino)­methyl]­(phenyl)­phosphino]­ethane (dpmppe) was prepared as a new tetraphosphine, and the corresponding rac and meso stereoisomers were successfully separated in view of their solubility difference in acetone. The substitution of PPh₃ into Pt­(PPh₃)₂(CCR)₂ (R = aryl) with rac- or meso-dpmppe gives Pt­(rac-dpmppe)­(CCR)₂ or Pt­(meso-dpmppe)­(CCR)₂, respectively. Using Pt­(rac-dpmppe)­(CCR)₂ or Pt­(meso-dpmppe)­(CCR)₂ as a precursor, PtAg₂ heterotrinuclear cluster complexes were synthesized and characterized by X-ray crystallography. Depending on the conformations of tetraphosphine, the structures of PtAg₂ complexes supported with rac- and meso-dpmppe are quite different. The higher molecular rigidity of rac-dpmppe-supported PtAg₂ complexes results in stronger phosphorescent emission than that of PtAg₂ species with meso-dpmppe. The high phosphorescent quantum yields (as high as 90.5%) in doping films warrant these PtAg₂ complexes as excellent phosphorescent dopants in organic light-emitting diodes (OLEDs). The peak current and external quantum efficiencies in solution-processed OLEDs are 61.0 cd A^–1 and 18.1%, respectively. Electroluminescence was elaborately modulated by modifying the substituent in aromatic acetylide and the conformations in tetraphosphine so as to achieve cyan, green, green-yellow, yellow, and orange-red emission.