Iridium(III)-Complexed Polydendrimers for Inkjet-Printing OLEDs: The Influence of Solubilizing Steric Hindrance Groups

With the great success of organic light-emitting diodes (OLEDs) based on thermal evaporation techniques, the development of printable materials for inkjet-printing high-performance OLEDs is particularly attractive yet challenging. In this paper, a set of printable Ir(III)-complexed polydendrimers, poly[bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)phenyl)pyridine][1-ethyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III)] (PIr-D1) and poly[bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)-2,6-dimethylphenyl)pyridine][1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III)] (PIr-D2), were designed and synthesized via ring-opening metathesis polymerization (ROMP). As a comparison, the iridium precursor complexes bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)phenyl)pyridine][1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole]iridium(III) (Ir-D1) and bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)-2,6-dimethylphenyl)pyridine][1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III) (Ir-D2) and the core structure bis[2-(2,4-difluorophenyl)pyridine] [1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III) (Ir-D0) were also synthesized and the corresponding OLEDs were fabricated. Compared with the dendritic iridium complexes Ir-D1 and Ir-D2, the resulting polydendrimers PIr-D2 and PIr-D2 showed enhanced film-forming properties, good thermal stability, and attractive ink rheological characteristics with a suitable viscosity for inkjet-printing. Promising device performance has been achieved for the resulting polydendrimers by both spin-coating and inkjet-printing, showing low driving voltages and relatively high current efficiencies and brightnesses. The results suggest that the construction of polydendritic Ir(III) complexes is an attractive design strategy for exploring efficient printable light-emitting materials for inkjet-printing high-performance OLEDs.