Highly efficient blue-emissive electroluminescence: nondestructive color regulation effect of orthogonal cyano-substitution in hybrid locally-excited and charge-transfer (HLCT) backbone emitters

Abstract

Blue-emissive materials are crucial in organic light emitting diodes (OLED). In this work, we report two highly efficient donor-acceptor materials PPIPO and PPIPOCN. PPIPO is constructed with phenanthroimidazole (PI) and oxadiazole groups, which is blue-emissive with high photoluminescent quantum yield (PLQY) of 86.2%. Furthermore, the cyano-substituted PPIPOCN realize more blue-shifted emission and equal PLQY comparing to PPIPO, which can be assigned to the formation of hybridized local and charge-transfer (HLCT) excited state. Significantly, the OLED based on the two materials both demonstrated decent performances, such as high external quantum efficiency (EQE) of 12.5% in PPIPO and nice blue purity of Commission Internationale de l'Eclairage y-coordinate (CIEy) of＜0.15 in PPIPOCN. This work provides a potential strategy for the designing of the high-efficiency and low-cost next-generation electro-fluorescent materials.