Ultraviolet (UV) light plays a crucial role in various applications, but currently, the efficiency of generating artificial UV light is low. The visible-to-ultraviolet (Vis-to-UV) system based on the triplet–triplet annihilation upconversion (TTA-UC) mechanism can be a viable solution. Metal-free multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are ideal photosensitizers (PSs) apart from the drawback of high photoluminescence quantum yields (PLQYs). Herein, we systematically investigated the impact of the heavy-atom effect (HAE) on the MR-TADF sensitizers. BNCzBr was then synthesized by incorporating a bromine atom into the skeleton of the precursor BNCz. Impressively, the internal HAE (iHAE) leads to a significantly decreased PLQY and a remarkably increased intersystem crossing quantum yield (Φ_ISC). Consequently, a higher upconversion quantum efficiency of 12.5% was realized. While the external HAE (eHAE) harms the UC performance. This work guides the further development of MR-TADF sensitizers for high-performance Vis-to-UV TTA-UC systems.

中文翻译：

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利用多重共振热激活延迟荧光 (MR-TADF) 敏化剂中的重原子效应：解锁高性能可见光到紫外光（可见光到紫外光）三重态融合上转换

紫外线（UV）光在各种应用中发挥着至关重要的作用，但目前，产生人造紫外线的效率较低。基于三重态-三重态湮没上转换（TTA-UC）机制的可见光到紫外（Vis-to-UV）系统可能是一个可行的解决方案。除了高光致发光量子产率（PLQY）的缺点之外，无金属多重共振热激活延迟荧光（MR-TADF）材料是理想的光敏剂（PS）。在此，我们系统地研究了重原子效应（HAE）对 MR-TADF 敏化剂的影响。然后通过将溴原子掺入前体 BNCz 的骨架中合成 BNCzBr。令人印象深刻的是，内部 HAE (iHAE) 导致 PLQY 显着降低，并且系统间交叉量子产率 (Φ _ISC ) 显着增加。因此，实现了 12.5% 的更高上转换量子效率。而外部 HAE (eHAE) 会损害 UC 性能。这项工作指导了用于高性能可见光到紫外 TTA-UC 系统的 MR-TADF 敏化剂的进一步开发。