Controlling excimer formation in indolo[3,2,1-]carbazole/9-carbazole based host materials for RGB PhOLEDs.

Three novel materials (, and ), based on the indolo[3,2,1-]carbazole and 9-carbazole building blocks, with high triplet energies ( > 2.80 eV) and good thermal stability ( > 101 °C) were synthesized, characterized and applied as host materials in PhOLED devices. In course of the preparation of the materials, an improved protocol for the synthesis of the indolo[3,2,1-]carbazole moiety has been developed. The careful molecular design of the title compounds allowed to avoid excimer formation of the indolo[3,2,1-]carbazole subunits in thin films. Therefore, the improved molecular design broadened the applicability of indolo[3,2,1-]carbazole host materials and significantly enhanced the efficiency of PhOLED devices based on these derivatives compared to previously reported indolo[3,2,1-]carbazole based compounds. Accordingly, employing the newly developed materials red (CE: 32.7 cd A, PE: 31.0 lm W, EQE: 20.4%), green (CE: 81.0 cd A, PE: 87.4 lm W, EQE: 21.5%) and blue (CE: 35.5 cd A, PE: 39.9 lm W, EQE: 18.0%) PhOLED devices with a remarkably low efficiency roll-off at 1000 cd m ( - red: 5%; green: 0%; blue: 6%) were fabricated.