Dendritic Carbene Metal Carbazole Complexes as Photoemitters for Fully Solution-Processed OLEDs

Abstract

Light-emitting carbene-metal amide complexes bearing first- and second-generation carbazole dendron ligands are reported, (AdL)M(Gn), (M = Cu and Au; Gn carbazole dendrimer generation, where n = 1 and 2; AdL = adamantyl-substituted cyclic (alkyl)(amino)carbene). The thermal stability of the complexes increases with each dendrimer generation. Cyclic voltammetry indicates that the highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels are largely unaffected by the size of the dendron, while first reduction and oxidation processes show a quasi-reversible character. The gold complexes in toluene at room temperature show photoluminescent quantum yields of up to 51.5% for the first and 78% for the second generation. Varied temperature transient photoluminescence decay is consistent with a thermally activated process, indicating a delayed fluorescence-type emission mechanism. Neat films show excited state lifetimes composed of prompt and dominant sub-microsecond delayed components, with radiative constants of up to 106 s–1. Solution-processed organic light-emitting diodes for first-generation copper and gold dendrimers (AdL)M(G1) have been fabricated with external quantum efficiencies of 5.5% for copper and 10.3% for gold at practical brightness.