In addition to emission efficiency and colors, emission characteristics such as preferentially horizontal emitting dipole orientation and resistance against concentration quenching are also highly desired for high-performance thermally activated delayed fluorescence (TADF) emitters. In this work, we report a simple and yet effective strategy for enhancing such emission performance of the pure red-to-near infrared (NIR) TADF emitter by introducing bulky aryl derivatives (-xylene) to the efficient emission core. Incorporating -xylene groups as the electronically inert pendants to the acceptor unit of the TADF emitter TPA–CN–N4-CH3 successfully retains favorable emission properties (e.g., pure red color chromaticity, nearly unitary photoluminescence quantum yield etc.) of the parent compound TPA–CN–N4 and yet also renders significantly higher horizontal emitting dipole ratio Θ// of ∼85 % with the more extended molecular configuration and reduced concentration quenching at very high concentrations in thin films. As a result, OLEDs adopting TPA–CN–N4-CH3 can demonstrate rather high EQEs of 29.8–32.1 % for pure red emission (625–650 nm) at low doping concentrations and decent EQEs of 18.9–27.5 % in the deep red to NIR range (650–700 nm) at higher doping concentrations. The results of this work shall provide a useful reference for development of efficient TADF emitters.

中文翻译：

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通过引入电子惰性吊坠提高红色 TADF 发射器的发射性能

除了发射效率和颜色之外，高性能热激活延迟荧光（TADF）发射器也非常需要发射特性，例如优先水平发射偶极子取向和抗浓度猝灭性。在这项工作中，我们报告了一种简单而有效的策略，通过将大体积芳基衍生物（-二甲苯）引入到高效发射核心来增强纯红光到近红外（NIR）TADF发射器的发射性能。将-二甲苯基团作为电子惰性侧基引入到TADF发射体TPA–CN–N4-CH3的受体单元中，成功地保留了母体化合物TPA的良好发射特性（例如，纯红色色度、近乎单一的光致发光量子产率等）。 –CN–N4，并且还具有显着更高的水平发射偶极子比 θ// 约 85%，具有更扩展的分子构型和在薄膜中非常高浓度下减少的浓度猝灭。因此，采用 TPA-CN-N4-CH3 的 OLED 在低掺杂浓度下可以表现出相当高的纯红色发射（625-650 nm）EQE 为 29.8-32.1%，在深红色到 18.9-27.5% 的不错的 EQE。较高掺杂浓度下的近红外范围 (650–700 nm)。本工作结果将为高效TADF发射器的开发提供有益的参考。