Development of Pure Green Thermally Activated Delayed Fluorescence Material by Cyano Substitution

• Published in: Advanced materials (Weinheim) 2022-08, Vol.34 (32), p.e2201778-n/a
• Main Authors: Oda, Susumu, Sugitani, Takumi, Tanaka, Hiroyuki, Tabata, Keita, Kawasumi, Ryosuke, Hatakeyama, Takuji
• Format: Article
• Language: English
• Subjects: Cyano groups; Efficiency; Emitters; Fluorescence; Light emitting diodes; Materials science; Materials substitution; multiple resonance effect; organic light‐emitting diodes; pure green; Purity; Quantum efficiency; Rate constants; thermally activated delayed fluorescence
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202201778

Multiple resonance (MR)‐effect‐induced thermally activated delayed fluorescence (TADF) materials have garnered significant attention because they can achieve both high color purity and high external quantum efficiency (EQE). However, the reported green‐emitting MR‐TADF materials exhibit broader emission compared to those of blue‐emitting ones and suffer from severe efficiency roll‐off due to insufficient rate constants of reverse intersystem crossing process (kRISC). Herein, a pure green MR‐TADF material (ν‐DABNA‐CN‐Me) with high kRISC of 105 s−1 is reported. The key to success is introduction of cyano groups into a blue‐emitting MR‐TADF material (ν‐DABNA), which causes remarkable bathochromic shift without a loss of color purity. The organic light‐emitting diode employing it as an emitter exhibits green emission at 504 nm with a small full‐width at half‐maximum of 23 nm, corresponding to Commission Internationale d'Éclairage coordinates of (0.13, 0.65). The device achieves a high maximum EQE of 31.9% and successfully suppresses the efficiency roll‐off at a high luminance. The bathochromic shift of a multiple‐resonance‐induced thermally activated delayed fluorescence material (ν‐DABNA) is achieved by introducing cyano groups. The cyano‐substituted material (ν‐DABNA‐CN‐Me) exhibits pure green emission with a small full‐width at half‐maximum. The fabricated organic light‐emitting diode device exhibits a high maximum external quantum efficiency (31.9%), which is maintained (28.5%) at 1000 cd m−2, demonstrating a minimum efficiency roll‐off.