Platinum(ii)–gold(i) heterotrinuclear complexes with N,N′-diarylamine-functionalized acetylide ligands for red electroluminescence

Abstract

In this work, 4-substituted phenylacetylides with electron-rich N,N′-diarylamine groups are used for the design of triphosphine-supported PtAu₂ complexes with red phosphorescence. Although PtAu₂ complex 1 with 4-ethynyl-N,N′-diphenylaniline displays orange emission in CH₂Cl₂ solution, highly efficient red phosphorescence is attained upon using 5-ethynyl-N,N′-diphenylthiophen-2-amine (2) or 2-ethynyl-4-phenyl-4H-dithieno[3,2-b:2′,3′-d]pyrrole (3) in place of 4-ethynyl-N,N-diphenylaniline (1). In contrast to the intense phosphorescence of complexes 1 and 3 in degassed CH₂Cl₂ solution at ambient temperature, complex 2 shows a quite weak phosphorescence as well as fluorescence of the acetylide ligand due to incomplete energy transfer from acetylide ligands to PtAu₂ centres. Since the phosphorescence efficiency of the doping films is as high as 98.3%, complexes 1–3 are excellent phosphorescent dopants in organic light-emitting diodes (OLEDs). Solution-processed OLEDs showed high-efficiency yellow emission for complex 1 (λ_EL = 567 nm), whereas orange-red phosphorescence for 2 (λ_EL = 624 nm) and deep red emission for 3 (λ_EL = 625 nm) with a peak external quantum efficiency of 16.5%, 8.4% and 13.6%, respectively.