Highly Efficient Blue/Deep-blue Circularly Polarized Electroluminescence with Small Efficiency Roll-Offs

Abstract

Developing efficient blue/deep-blue circularly polarized organic light-emitting diodes (CP-OLEDs) with small efficiency roll-off remains a great challenge for wide color gamut and high contrast 3D displays. Here, two pairs of chiral stable enantiomers, (R/S)-PPI-OBN-CN and (R/S)-PyI-OBN-CN, composed of imidazole derivatives phenanthroimidazole (PPI) and pyrenoimidazole (PyI) donors, and chiral group of (R/S)-octahydro-binaphthol (OBN-CN) acceptor are designed. These new blue/deep-blue molecular architectures exhibit excellent thermal and electrochemical stabilities, hybrid local and charge transfer (HLCT) excited state, and clear CPL characteristics with dissymmetry factors (|g_PL|) of 1.57 × 10⁻³/2.49 × 10⁻³ in the neat films. Moreover, the CP-OLEDs based on (R/S)-PPI-OBN-CN and (R/S)-PyI-OBN-CN exhibit the deep-blue/pure-blue emission with the CIE coordinates of (0.15, 0.08) and (0.15, 0.14), the maximum external quantum efficiencies (EQEs) of 7.25% and 8.11% and very small efficiency roll-offs of 17.6% and 1.8% at the luminescence of 1000 cd m⁻², respectively. Even when the brightness is increased to 10000 cd m⁻², (R/S)-PyI-OBN-CN-based device could still maintain as high as 6.68%. Obvious circularly polarized electroluminescence (CPEL) activities with the EL dissymmetry factors (g_EL) of +1.54 × 10⁻³/−1.63 × 10⁻³ and +1.95 × 10⁻³/−1.72 × 10⁻³ are also recorded. These are the first highly efficient blue/deep-blue CP-OLEDs based on “hot exciton” enantiomers.