Platinum(ii)–gold(i) heterotrinuclear complexes with N,N′-diarylamine-functionalized acetylide ligands for red electroluminescence†
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 (λEL = 567 nm), whereas orange-red phosphorescence for 2 (λEL = 624 nm) and deep red emission for 3 (λEL = 625 nm) with a peak external quantum efficiency of 16.5%, 8.4% and 13.6%, respectively.