Polycyclic π‐conjugated compounds that contain tricoordinate boron atoms at their periphery represent an attractive class of materials with electron‐accepting character. Their molecular design generally requires the introduction of a bulky aryl group onto the boron atom, where it provides predominantly kinetic stabilization. The addition of extra functionality to the aryl group on the boron atom can be expected to further expand the potential utility of this class of materials. Herein, we report the synthesis of a series of boracyclic π‐conjugated molecules with firm ortho B∙∙∙N nonbonding interactions by introducing N‐containing electron‐donors at the ortho‐positions of the aryl group on the boron atom. X‐ray crystallographic analysis revealed that the combination of a planar boracyclic π‐skeleton with only sp2 carbons and a strong electron‐donating phenothiazine moiety results in a particularly short B∙∙∙N distance. Theoretical study provided insights into the inherent nature of the B∙∙∙N interaction. Owing to their donor–acceptor (D–A) structures, these molecules exhibit substantially red‐shifted fluorescence in solution, albeit that the fluorescence quantum yields (ΦF) are low. In contrast, when incorporated into films, these compounds exhibit thermally activated delayed fluorescence (TADF) with improved ΦF values. Organic light‐emitting diodes (OLEDs) fabricated using the ortho‐donor‐substituted derivatives exhibit orange‐red electroluminescence.

中文翻译：

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超越空间保护的硼环π电子体系的双邻位供体修饰以产生热激活延迟荧光材料

外围含有三配位硼原子的多环π共轭化合物代表了一类具有电子接受特性的有吸引力的材料。它们的分子设计通常需要在硼原子上引入一个大的芳基，以提供主要的动力学稳定性。在硼原子上的芳基上添加额外的官能团有望进一步扩大此类材料的潜在用途。在此，我们报道了通过在硼原子芳基的邻位引入含氮电子给体，合成了一系列具有牢固的邻位B∙∙∙N非键相互作用的硼环π共轭分子。 X射线晶体学分析表明，仅含有sp2碳的平面硼环π骨架与强给电子吩噻嗪部分的组合导致B∙∙∙N距离特别短。理论研究为 B∙∙∙N 相互作用的内在本质提供了见解。由于它们的供体-受体（D-A）结构，这些分子在溶液中表现出明显的红移荧光，尽管荧光量子产率（ΦF）很低。相比之下，当掺入薄膜中时，这些化合物表现出热激活延迟荧光 (TADF)，并具有改善的 ΦF 值。使用邻位供体取代衍生物制造的有机发光二极管（OLED）表现出橙红色电致发光。