Photophysical and Electroluminescent Properties of PtAg<sub>2</sub> Acetylide Complexes Supported with <i>meso</i>- and <i>rac</i>-Tetraphosphine

1,2-Bis­[[(diphenylphosphino)­methyl]­(phenyl)­phosphino]­ethane (dpmppe) was prepared as a new tetraphosphine, and the corresponding <i>rac</i> and <i>meso</i> stereoisomers were successfully separated in view of their solubility difference in acetone. The substitution of PPh<sub>3</sub> into Pt­(PPh<sub>3</sub>)<sub>2</sub>(CCR)<sub>2</sub> (R = aryl) with <i>rac</i>- or <i>meso</i>-dpmppe gives Pt­(<i>rac</i>-dpmppe)­(CCR)<sub>2</sub> or Pt­(<i>meso</i>-dpmppe)­(CCR)<sub>2</sub>, respectively. Using Pt­(<i>rac</i>-dpmppe)­(CCR)<sub>2</sub> or Pt­(<i>meso</i>-dpmppe)­(CCR)<sub>2</sub> as a precursor, PtAg<sub>2</sub> heterotrinuclear cluster complexes were synthesized and characterized by X-ray crystallography. Depending on the conformations of tetraphosphine, the structures of PtAg<sub>2</sub> complexes supported with <i>rac</i>- and <i>meso</i>-dpmppe are quite different. The higher molecular rigidity of <i>rac</i>-dpmppe-supported PtAg<sub>2</sub> complexes results in stronger phosphorescent emission than that of PtAg<sub>2</sub> species with <i>meso</i>-dpmppe. The high phosphorescent quantum yields (as high as 90.5%) in doping films warrant these PtAg<sub>2</sub> 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<sup>–1</sup> 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.