The conflict between improving reverse intersystem crossing (RISC) and singlet radiation is one of the key fundamental issues for thermally activated delayed fluorescence (TADF) materials. Here, we demonstrate that the excited-state structural relaxation can be effectively suppressed through fixing the molecular configuration with intramolecular C–H···F hydrogen bonds. The resulted TADF emitter 7CzFDCF₃DPh reveals the nearly identical ground state, the first singlet (S₁) and triplet (T₁) excited-state configurations. Therefore, the singlet-triplet energy gap is reduced to <0.06 eV, establishing the multiple RISC channels through either electronic or vibrational couplings. 7CzFDCF₃DPh reveals a state-of-the-art RISC rate constant (k_RISC) of ~10⁶ s⁻¹, accompanied by the doubled RISC efficiency (φ_RISC) as high as 97%. The dramatically accelerated TADF renders the photoluminescence and electroluminescence quantum efficiencies more than 90% and 20% for 7CzFDCF₃DPh. These results manifest the significance of the configuration fixation for improving TADF performance.

逆向系统间交叉（RISC）和单线态辐射之间的冲突是热激活延迟荧光（TADF）材料的关键基本问题之一。在这里，我们证明了通过固定带有分子内C–H··F氢键的分子构型可以有效地抑制激发态结构弛豫。所得的TADF发射极7CzFDCF ₃ DPh显示出几乎相同的基态，第一单重态（S ₁）和三重态（T ₁）激发态构型。因此，单重态-三重态能隙减小至<0.06 eV，通过电子或振动耦合建立多个RISC通道。7CzFDCF ₃ DPh显示了最新的RISC速率常数（ķ _RISC）〜10的^6个小号^-1，伴随一倍RISC效率（φ _RISC）高达97％。急剧加速的TADF使7CzFDCF ₃ DPh的光致发光和电致发光量子效率超过90％和20％。这些结果表明配置固定对于提高TADF性能的重要性。