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

Cationic Au4Ag2 heterohexanuclear aromatic acetylides cluster complexes supported by bis(2-diphenylphosphinoethyl)phenylphosphine (dpep) are prepared. The Au4Ag2 cluster structure originating from the combination of one anionic [Au(CCR)(2)](-) with one cationic [Au3Ag2(dpep)(2)(CCR)(2)](3+) through the formation of Ag-acetylide (2)-bonds is highly stabilized by Au-Ag and Au-Au contacts. The Au4Ag2 alkynyl cluster complexes are moderately phosphorescent in the fluid CH2Cl2 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)[ (aromatic acetylide) s/p (Au)] (LMCT)-L-3 parentage with a noticeable Au4Ag2 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 Au4Ag2 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.