Photoluminescence and electroluminescence of cationic PtAu2 heterotrinuclear complexes with aromatic acetylides

Abstract

Cationic PtAu₂ heterotrinuclear complexes [PtAu₂(dpmp)₂(CCR)₂]²⁺ (dpmp = bis(diphenylphosphinomethyl)phenylphosphine, R = aryl) of aromatic acetylides were prepared. The PtAu₂ structures are supported through doubly bridging dpmp and stabilized by a significant Pt–Au interaction. They are highly phosphorescent in fluid CH₂Cl₂ solution (Φ_em = 23.5%–78.9%), the solid state (Φ_em = 15.4%–70.2%), the PMMA film (Φ_em = 39.9%–71.7%) and the doping film of 61% TCTA : 31% OXD-7 : 8% PtAu₂ complex (Φ_em = 16.9%–67.9%). The phosphorescence arises mainly from ³[π (CCR) → π* (dpmp)] ³LLCT and ³[π (CCR) → s/p (PtAu₂)] ³LMCT triplet excited states for carbazole-acetylide complexes, whereas other complexes display a ³LLCT character mixed with noticeable PtAu₂ centered ³[d → s/p] parentage. Utilizing a mixed host composed of hole-transporting TCTA and electron-transporting OXD-7 doped with 8% PtAu₂ species as a light-emitting layer and CuSCN as a hole-transporting layer through an orthogonal solution process, the devices exhibit highly efficient electrophosphorescence with the highest current efficiency (CE_max) of 51.7 cd A⁻¹ and external quantum efficiency (EQE_max) of 14.5%. The efficiency roll-off is small in the practical brightness range of 500–5000 cd m⁻². The PtAu₂ complexes with carbazole-acetylides display a higher electroluminescence efficiency ascribed to their better hole-transporting character as well as more facile energy transfer from mixed host materials.