Chiral electron transporting material for circularly polarized organic light-emitting diode

Circularly polarized organic light-emitting diode (CP-OLED) has attracted increasing interest for its efficient ability to generate circularly polarized light directly. So far, many CP-OLEDs were successfully fabricated with chiral emitters or chiral hosts. In this study, a new strategy based on chiral electron transporting layer is proposed to construct CP-OLEDs. A pair of chiral electron transporting materials, 1,3,5-tris((R/S)-4-isopropyl-4,5-dihydrooxazol-2-yl)benzene ((R/S)-TOxiPr), are firstly designed and synthesized. The crystalline films of (R/S)-TOxiPr show circularly polarized photoluminescence with photoluminescence dissymmetry factors of -0.067 and +0.041, respectively. The CP-OLEDs based on (R/S)-TOxiPr and three types of achiral emitters all exhibit circularly polarized electroluminescence, showing feasibility and strong versatility of this new strategy. The mechanism is attributed to in-situ electrical excitation instead of simply light filtering of non-circularly polarized light. This work demonstrates a new approach for realizing circularly polarized electroluminescence which may provide a valuable strategy to develop CP-OLEDs.