【Angew.Chem.】西安交通大学王栋东|氮调控轨道适配型 π 共轭拓展，平衡激发态组分、抑制振动展宽，构筑红移窄带多共振热活化延迟荧光发光材料#

Figure 1. Nitrogen-mediated MR orbital-compatible π-extension strategy: modulating vibronic coupling to enable narrowband emission in π-extended BN-MR emitters. (a) Frontier orbitals analysis of representative benzene-fused B-N MR-emitters. (b) Design of MR-orbit-compatible BN-MR emitters via pyridine-type N-Doping; the inset table provides a parametric comparison of reference BN-TP and BNCz-BQ/BNCz-PQ/BNCz-PMQ on FC-active vibronic modes, LRCT/SRCT ratios, emission wavelength, and FWHM.#

Figure 2. (a) Molecular design of the π-extended BN-MR emitters. The reference structure BN-TP is partitioned into three fused conjugated segments (1–3), and the target compounds are constructed via rational site-specific N-doping at designated positions of the conjugated backbone. (b) Frontier molecular orbital distributions and calculated HOMO-LUMO gaps for all emitters. (c) Charge transfer ratio analysis (LRCT/SRCT) and Δ_E_ST, with summarized CT contributions in the inset table.#

在对设计分子进行拓扑层面的精密定量分析时，如图2所示，通过碎片化前线轨道重叠与电荷转移比例分析发现，仅引入单氮或过量引入氮原子都无法达到理想的调控效果。例如在过量引入氮原子的分子中，过度的电荷离域反而使长程电荷转移比例激增至37.48%，导致其向传统电荷转移材料退化。相反地，精准设计的候选分子BNCz-PQ通过位点特异性掺杂，使外围片段的最高占据分子轨道与最低未占据分子轨道贡献达到了9.00%和8.20%的完美平衡，成功将长程电荷转移比例压低至17.34%，在保持全骨架多共振特征的同时，构筑了近乎完美的交替轨道拓扑。

Figure 3. (a) S0/S1 geometry overlays and calculated RMSD values for BN-TP and N-doped BN-MR emitters. (b) Normal-mode decomposition of total reorganization energy for all investigated emitters, with key vibrational modes annotated.#

这种优异的轨道兼容性在激发态动力学层面上展现出了巨大的威力。如图3所示，激发态与基态几何结构的重叠模拟（RMSD）显示，轨道兼容性最佳的BNCz-PQ拥有最低的结构驰豫度，其总重组能被大幅压低至408.6 $\text{cm}^{-1}$。简正模式分解实验进一步证实，精准的氮掺杂异常显著地抑制了中低频区域的骨架拉伸与面外扭转振动。相较于传统扩展共轭分子中被强烈激活并导致光谱宽化的非辐射损失通道，新分子极大削弱了电荷转移过程中的激振耦合，从而在分子源头上锁定了窄带发光的基因。

Figure 4. Photophysical characterization of BNCz-BQ, BNCz-PQ, and BNCz-PMQ: (a–c) UV–vis absorption and fluorescence emission spectra in toluene (298 K), with emission maxima and FWHM labeled. (d–f) 77 K fluorescence and phosphorescence spectra in toluene. (g, h) Transient PL decay curves in 1 wt% doped DMAC-BP films. (i) fluorescence emission spectra of 1 wt% emitter-doped DMAC-BP films.#

在打通理论瓶颈后，研究团队通过创新的内分子氧化脱氢环化策略成功合成了目标产物，克服了电子缺陷型芳环在传统Scholl反应中难以成环的物料局限。光物理性能测试表明，如图4所示，设计的三种化合物在甲苯溶液中均呈现出高亮度的绿光发射。其中，经过精细轨道调控的BNCz-PQ表现最为惊艳，其溶液发射峰位于511 nm，半峰全宽仅为24 nm，相较于未掺杂氮的参照分子大幅收窄了10 nm，同时展现出高达93%的绝对荧光产率。通过高低温度瞬态光谱测量也清晰证实了其高效的三重态激子反向系间窜跃（RISC）特征，即典型的多共振热活化延迟荧光行为。

Figure 5. (a) Theoretical vibrationally resolved PL spectrum of the reference compound BN-TP, with the blue solid line representing the Gaussian-broadened simulated spectrum and the gray bars denoting the individual |0⟩ → |v⟩ vibrational transitions. The FWHM of the simulated spectrum is labeled, and the characteristic vibrational transitions contributing to spectral broadening, along with their corresponding frequency ranges, are highlighted. (b–d) Experimental (toluene, green dashed) and theoretical (Gaussian-broadened, blue solid) vibrationally resolved PL spectra of N-doped emitters BNCz-BQ, BNCz-PQ, and BNCz-PMQ.#

为了进一步揭示光谱收窄的物理本质，研究人员计算了振动分辨电子光谱。如图5所示，实验光谱与理论高斯拓扑拓宽光谱高度吻合，再次有力印证了“轨道调控抑制长程电荷转移，进而削弱振动耦合以实现窄带发射”这一设计哲学的正确性。 excessive氮掺杂的分子由于高频振动的加剧，光谱明显偏宽，从反面印证了位点特异性调控的决定性意义。

Figure 6. Performance of 1 wt% doped OLEDs based on BNCz-BQ, BNCz-PQ, and BNCz-PMQ. (a–c) EL spectra at 1000 cd m−2, with emission maxima, FWHM, CIE coordinates, and device operating photos. (d–f) EQE–luminance curves, comparing sensitized (sensitizer) and single-host (single host) devices, with key EQE values labeled. (g–h) J–V–L characteristics for single-host devices and sensitized devices. (i) Device structure.#

最终，研究团队将这些新型发光材料制备成有机发光二极管（OLED）器件以评估其实际应用潜力。如图6所示，在常规的单发光层主体器件中，各材料均展现出极高的色纯度，其中BNCz-PQ器件的电致发光峰位于508 nm，半峰全宽低至27 nm，CIE色坐标达到色饱和度极高的（0.18, 0.65）。为了解决高亮度下可能存在的激子湮灭问题，研究者进一步引入了膦光辅助热活化延迟荧光敏化（pTSF）策略。优化后的敏化器件在保持超窄光谱的同时，能量利用效率和载流子平衡得到全面升华，BNCz-PQ敏化器件一举斩获了27.7%的极大外量子效率和超过153400 $\text{cd m}^{-2}$的极高亮度。更为难能可贵的是，该器件表现出极具应用前景的效率滚降抑制效应，在1000 $\text{cd m}^{-2}$和10000 $\text{cd m}^{-2}$的实用高亮度下，外量子效率依然能坚挺地维持在27.1%和23.6%。