Efficient Circularly Polarized Electroluminescence Based on Chiral MR-TADF Materials with Innovative Planar Structure Design Strategy

Abstract

Chiral multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) emitters have obtained attention due to their potential in organic light-emitting diodes (CP-OLEDs) with circularly polarized luminescence (CPL). Moreover, the devices always rely on the doping concentration due to the concentration aggregation-caused quenching of CP-MR-TADF emitters. Herein, three MR-TADF materials (p-ICz-N-BN, m-ICz-N-BN and m-prCz-N-BN) are presented by face-to-face arrangement of indolo[3,2,1-jk]carbazole and MR-TADF fluorophore sterically on naphthalene bridge, showing emissions peaking at 496–499 nm with full-width at half-maximum values of 23–26 nm and photoluminescence quantum yields of 91%–98%, respectively. Because of the asymmetric and steric hindrance structures, both m-ICz-N-BN and m-prCz-N-BN are separated into innovative planar enantiomers, exhibiting symmetric CPL spectra with dissymmetry factors (|g_PL|) of up to 1.1 × 10⁻³ and 2.3 × 10⁻³ in toluene and films, respectively. Furthermore, the OLEDs with p-ICz-N-BN, m-ICz-N-BN, and m-prCz-N-BN illustrate maximum external quantum efficiencies of 31.5%, 33.7%, and 32.4%, respectively, and still remain at high levels even at the 20 wt.% doping concentration with almost unchanged emission spectra. Additionally, the CP-OLEDs with R/S-m-ICz-N-BN and R/S-m-prCz-N-BN display |g_EL| factors of 1.88 × 10⁻³ and 1.89 × 10⁻³, respectively.