Diindolocarbazole - achieving multiresonant thermally activated delayed fluorescence without the need for acceptor units

• Published in: Materials horizons 2022-03, Vol.9 (3), p.168-18
• Main Authors: Hall, David, Stavrou, Kleitos, Duda, Eimantas, Danos, Andrew, Bagnich, Sergey, Warriner, Stuart, Slawin, Alexandra M. Z, Beljonne, David, Köhler, Anna, Monkman, Andrew, Olivier, Yoann, Zysman-Colman, Eli
• Format: Article
• Language: English
• Subjects: Computer architecture; Emitters; Energy gap; Fluorescence; Organic light emitting diodes; Photoluminescence
• ISSN: 2051-6347; 2051-6355
• DOI: 10.1039/d1mh01383a

In this work we present a new multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter paradigm, demonstrating that the structure need not require the presence of acceptor atoms. Based on an in silico design, the compound DiICzMes 4 possesses a red-shifted emission, enhanced photoluminescence quantum yield, and smaller singlet-triplet energy gap, Δ E ST , than the parent indolocarbazole that induces MR-TADF properties. Coupled cluster calculations accurately predict the magnitude of the Δ E ST when the optimized singlet and triplet geometries are used. Slow yet optically detectable reverse intersystem crossing contributes to low efficiency in organic light-emitting diodes using DiICzMes 4 as the emitter. However, when used as a terminal emitter in combination with a TADF assistant dopant within a hyperfluorescence device architecture, maximum external quantum efficiencies of up to 16.5% were achieved at CIE (0.15, 0.11). This represents one of the bluest hyperfluorescent devices reported to date. Simultaneously, recognising that MR-TADF emitters do not require acceptor atoms reveals an unexplored frontier in materials design, where yet greater performance may yet be discovered. We present a new multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter paradigm, demonstrating that the structure need not require the presence of acceptor atoms.