Blue hyperphosphorescence based on green Ir(III) sensitizer with dual CF3 substituted imidazo[4,5-c]pyridin-2-ylidene cyclometalates

Abstract

Hyperphosphorescent organic light-emitting diodes (HPOLEDs) are drawing increased attention, as the efficient Förster resonance energy transfer (FRET) from phosphorescent sensitizer to the narrowband fluorescent terminal emitter may give improved performances. In this work, we reported a class of Ir(III) phosphors based on the di-trifluoromethyl (CF₃) substituted imidazo[4,5-c]pyridin-2-ylidene chelates; i.e., (L_6F) and (L_6FB). The f-isomers exhibited efficient blue emission with peak max. 443 − 462 nm, while m-counterparts exhibited green emission between 501 – 512 nm in degassed toluene solution. The theoretical calculation indicates divergent MLCT, LLCT and ILCT contributions for distinctive isomers. OLEDs based on dopant m-Ir(L_6FB)₃ exhibited green luminescence at 505 nm, EQE_max of 20.3 % and CIE_x,y of (0.277, 0.462), while respective HPOLEDs with terminal emitter ν-DABNA showed blue hyperphosphorescence peaking at 468 nm, EQE_max of 25.2 %, CIE_x,y of (0.174, 0.204) and EQE of 22.7 % at 1000 cd·m^-2. Therefore, our finding demonstrates the effective conversion of the green electrophosphorescence to blue hyperphosphorescence via the rapid FRET process.