Abstract：
Carbene-metal-amides (CMAs) are emerging delayed fluorescence materials for organic light-emitting diode (OLED) applications. CMAs possess fast, efficient emission owing to rapid forward and reverse intersystem crossing (ISC) rates. The resulting dynamic equilibrium between singlet and triplet spin manifolds distinguishes CMAs from most purely organic thermally activated delayed fluorescence emitters. However, direct experimental triplet characterization in CMAs is underutilized, limiting our detailed understanding of the ISC mechanism. In this work, we combine time-resolved spectroscopy with tuning of state energies through environmental polarity and metal substitution, focusing on the interplay between charge-transfer (3CT) and local exciton (3LE) triplets. Unlike previous photophysical work, we investigate evaporated host : guest films of CMAs and small-molecule hosts for increased device relevance. Transient absorption reveals an evolution in the triplet excited-state absorption (ESA) consistent with a change in orbital character between hosts with differing dielectric constants. Using quantum chemical calculations, we simulate ESAs of the lowest triplet states, highlighting the contribution of only 3CT and donor-moiety 3LE states to spectral features, with no strong evidence for a low-lying acceptor-centered 3LE. Thus, our work provides a blueprint for understanding the role of triplet excited states in CMAs which will enable further intelligent optimization of this promising class of materials.
摘要：
卡宾金属酰胺（CMA）是用于有机发光二极管（OLED）应用的新兴延迟荧光材料。CMA拥有快速，由于快速的正向和反向系统间交叉(ISC)速率而产生的高效排放。单重态和三重态自旋歧管之间的动态平衡使CMA与大多数纯有机热激活延迟荧光发射体区分开。然而,CMA中的直接实验三重态表征未得到充分利用，限制了我们对ISC机制的详细了解。在这项工作中,我们将时间分辨光谱与通过环境极性和金属替代来调节状态能量相结合，重点研究电荷转移(3CT)和局部激子(3LE)三重态之间的相互作用。与以前的光物理工作不同，我们研究了蒸发的宿主：CMA和小分子宿主的客体膜，以增加设备相关性。瞬态吸收揭示了三重激发态吸收（ESA）的演变，这与具有不同介电常数的主体之间的轨道特性变化相一致。利用量子化学计算,我们模拟最低三重态的ESA，强调只有3CT和供体部分3LE状态对光谱特征的贡献，没有强有力的证据表明低洼的以受体为中心的3LE。因此，我们的工作为理解三重激发态在CMA中的作用提供了蓝图，这将使这种有前途的材料能够进一步智能优化。
