Exploring strategies to enhance reverse intersystem crossing (RISC) is of great significance to develop efficient thermally activated delayed fluorescent (TADF) molecules. In this study, we investigate the substantial impact of nonplanar structure on improving the rate of RISC (k_RISC). Three emitters based on spiroacridine donors are developed to evaluate this hypothesis. All molecules exhibit high photoluminescent quantum yields (PLQYs) of 96–98% due to their rigid donor and acceptor. Leveraging the synergistic effects of heavy element effect and nonplanar geometry, S2-TRZ exhibits an accelerated k_RISC of 24.2 × 10⁵ s⁻¹ compared to the 11.1 × 10⁵ s⁻¹ of S1-TRZ, which solely incorporates heavy atoms. Additionally, O1-TRZ possesses a further lower k_RISC of 9.42 × 10⁵ s⁻¹ because of the absence of these effects. Remarkably, owing to the high PLQYs and suitable TADF behaviors, devices based on these emitters exhibit state-of-the-art performance, including a maximum external quantum efficiency of up to 40.1% and maximum current efficiency of 124.7 cd A⁻¹. More importantly, devices utilizing S2-TRZ as an emitter achieve a relieved efficiency roll-off of only 7% under 1000 cd m⁻², in contrast to the 12% for O1-TRZ and 11% for S1-TRZ, respectively. These findings advance our fundamental understanding of TADF processes for high-performance electroluminescent devices.

中文翻译：

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非平面结构加速 TADF 发射器的反向系间穿越：近 40% EQE 并缓解效率滚降


探索增强反向系间窜越（RISC）的策略对于开发高效的热激活延迟荧光（TADF）分子具有重要意义。在本研究中，我们研究了非平面结构对提高 RISC 率 (k _RISC ) 的实质性影响。开发了三种基于螺吖啶供体的发射器来评估这一假设。由于其刚性的供体和受体，所有分子都表现出 96-98% 的高光致发光量子产率 (PLQY)。利用重元素效应和非平面几何的协同效应，与 11.1 × 11.1 × 10 ⁵ s ⁻¹ 相比，S2-TRZ 的加速 k _RISC 为 24.2 × 10 ⁵ s ⁻¹ S1-TRZ的10 ⁵ s ⁻¹ ，仅包含重原子。此外，由于不存在这些效应，O1-TRZ 的 k _RISC 更低，为 9.42 × 10 ⁵ s ⁻¹ 。值得注意的是，由于高 PLQY 和合适的 TADF 行为，基于这些发射器的器件表现出最先进的性能，包括高达 40.1% 的最大外部量子效率和 124.7 cd A 的最大电流效率 ⁻¹ 下仅实现 7% 的缓解效率滚降，而 O1-TRZ 为 12%，S1-为 11%。分别为TRZ。这些发现增进了我们对高性能电致发光器件 TADF 工艺的基本理解。