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

Three novel materials ( 5CzICz , Cz2 ICz and Cz3 ICz ), based on the indolo[3,2,1- jk ]carbazole and 9 H -carbazole building blocks, with high triplet energies ( E T > 2.80 eV) and good thermal stability ( T g > 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- jk ]carbazole moiety has been developed. The careful molecular design of the title compounds allowed to avoid excimer formation of the indolo[3,2,1- jk ]carbazole subunits in thin films. Therefore, the improved molecular design broadened the applicability of indolo[3,2,1- jk ]carbazole host materials and significantly enhanced the efficiency of PhOLED devices based on these derivatives compared to previously reported indolo[3,2,1- jk ]carbazole based compounds. Accordingly, employing the newly developed materials red (CEmax : 32.7 cd A-1 , PEmax : 31.0 lm W-1 , EQEmax : 20.4%), green (CEmax : 81.0 cd A-1 , PEmax : 87.4 lm W-1 , EQEmax : 21.5%) and blue (CEmax : 35.5 cd A-1 , PEmax : 39.9 lm W-1 , EQEmax : 18.0%) PhOLED devices with a remarkably low efficiency roll-off at 1000 cd m-2 ( Cz2 ICz - red: 5%; green: 0%; blue: 6%) were fabricated.