Phosphorescent Cationic Au₄Ag₂ Alkynyl Cluster Complexes for Efficient Solution‐Processed Organic Light‐Emitting Diodes

Abstract

Cationic Au 4 Ag 2 heterohexanuclear aromatic acetylides cluster complexes supported by bis(2‐diphenylphosphinoethyl)phenylphosphine (dpep) are prepared. The Au 4 Ag 2 cluster structure originating from the combination of one anionic [Au(C≡CR) 2 ] − with one cationic [Au 3 Ag 2 (dpep) 2 (C≡CR) 2 ] 3+ through the formation of Ag−acetylide η 2 ‐bonds is highly stabilized by Au–Ag and Au–Au contacts. The Au 4 Ag 2 alkynyl cluster complexes are moderately phosphorescent in the fluid CH 2 Cl 2 solution, but exhibit highly intense phosphorescent emission in solid state and film. As revealed by theoretical computational studies, the phosphorescence is ascribable to significant 3 [π (aromatic acetylide) → s/p (Au)] 3 LMCT parentage with a noticeable Au 4 Ag 2 cluster centered 3 [d → s/p] triplet state. Taking advantage of mCP and OXD‐7 as a mixed host with 20 wt% dopant of phosphorescent Au 4 Ag 2 cluster complex in the emitting layer, solution‐processed organic light‐emitting diodes (OLEDs) exhibit highly efficient electrophosphorescence with the maximum current, power, and external quantum efficiencies of 24.1 cd A −1 , 11.6 lm W −1 , and 7.0%, respectively. Introducing copper(I) thiocyanate (CuSCN) as a hole‐transporting layer onto the PEDOT:PSS hole‐injecting layer through the orthogonal solution process induces an obvious improvement of the device performance with lower turn‐on voltage and higher electroluminescent efficiency.