Efficient circularly polarized multiple resonance thermally activated delayed fluorescence from B,N-embedded hetero[8]helicene enantiomers

Abstract

Helicene-based circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) materials are promising for ultra-high-definition and 3D displays, but most of them encounter potential problems such as easy racemization during the thermal deposition process, low luminous efficiency, and low luminescence dissymmetry factor (<i>g</i> _lum), making the development of efficient circularly polarized organic light-emitting diodes (CP-OLEDs) a significant challenge. Here, we report a pair of CP-MR-TADF enantiomers with high-order B,N-embedded hetero[8]helicene, (<i>P</i>/<i>M</i>)-BN-TP-ICz, by fusing two MR chromophores, DtCzB and indolo[3,2,1-<i>jk</i>]carbazole (ICz). BN-TP-ICz exhibits green emission in toluene with a peak of 531 nm and a full-width at half-maximum (FWHM) of 36 nm. The optimized CP-OLEDs with enantiomers (<i>P</i>/<i>M</i>)-BN-TP-ICz exhibit green emission with peaks of 540 nm, FWHMs of 38 nm and Commission Internationale de L'Eclairage coordinates of (0.33, 0.65). Moreover, they showcase maximum external quantum efficiencies (EQEs) of 32.0%, with <i>g</i> _ELs of +6.49 × 10^-4 and -7.74 × 10^-4 for devices based on (<i>P</i>)-BN-TP-ICz- and (<i>M</i>)-BN-TP-ICz, respectively.