Ning ZiYe, Lv LingLing, Zhang YanYing, Meng YiZi, Tang BoWen
College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui, Gansu 741001, China.
Supercomputing Center for Theoretical Chemistry, Tianshui Normal University, Tianshui, GanSu 741001, China.
J Phys Chem A. 2025 Jun 19;129(24):5300-5312. doi: 10.1021/acs.jpca.5c02143. Epub 2025 Jun 4.
The investigation of thermally activated delayed fluorescence (TADF) in carbene-metal-amide (CMA) complexes reveals that structurally flexible ligands can demonstrate significant TADF characteristics. A series of four conformationally flexible copper(I) complexes featuring cyclic alkyl amino carbene (CAAC) and 10-phenothiazine-5,5-dioxide (Ptz) ligands were systematically studied using quantum chemical calculations. The study examines the impact of two key structural parameters, namely torsion angle φ (CAAC-Cu(I)-Ptz-1: perpendicular; CAAC-Cu(I)-Ptz-2 and CAAC-Cu(I)-Ptz-3: coplanar; CAAC-Cu(I)-Ptz-4: anticoplanar) and tilt angle β (near-planar arrangement: CAAC-Cu(I)-Ptz-3 > CAAC-Cu(I)-Ptz-2), on the photophysical properties of conformations. Geometrical and excited-state analyses indicate that CAAC-Cu(I)-Ptz-1, CAAC-Cu(I)-Ptz-2, and CAAC-Cu(I)-Ptz-4 conformations are observed to have similar excited-state transitions, but their torsion angles critically influence energy gap variations. Specifically, the energy differences between excited states of CAAC-Cu(I)-Ptz-2 and CAAC-Cu(I)-Ptz-3 are 0.10 and 0.20 eV, respectively, due to distinct torsion spans. Notably, the increased tilt angle β in CAAC-Cu(I)-Ptz-3 diminishes the contribution of Cu, with the lowest triplet state (T) displaying 47% ligand-to-ligand charge transfer (LLCT) and 28% metal-to-ligand charge transfer (MLCT) character. The combined minimum energy crossing point (MECP) and spin-orbit coupling (SOC) analyses elucidate the effect on reverse intersystem crossing (RISC) rates: CAAC-Cu(I)-Ptz-3 (0.41 eV MECP barrier) and CAAC-Cu(I)-Ptz-1 (SOC = 4.35 cm) are confirmed to suppress RISC rates (1.09 × 10 and 1.09 × 10 s, respectively), while enhanced RISC rates are achieved through reduced MECP barriers and strengthened SOC interactions by CAAC-Cu(I)-Ptz-2 and CAAC-Cu(I)-Ptz-4 (1.68 × 10 and 3.87 × 10 s, respectively). These findings highlight the vital role of ligand flexibility in the photophysical properties of CMA emitters, offering valuable guidance for designing efficient TADF materials.
对卡宾 - 金属 - 酰胺（CMA）配合物中的热激活延迟荧光（TADF）进行研究发现，结构灵活的配体可展现出显著的TADF特性。使用量子化学计算系统地研究了一系列四种具有环状烷基氨基卡宾（CAAC）和10 - 吩噻嗪 - 5,5 - 二氧化物（Ptz）配体的构象灵活的铜（I）配合物。该研究考察了两个关键结构参数，即扭转角φ（CAAC - Cu（I） - Ptz - 1：垂直；CAAC - Cu（I） - Ptz - 2和CAAC - Cu（I） - Ptz - 3：共面；CAAC - Cu（I） - Ptz - 4：反平行）和倾斜角β（近平面排列：CAAC - Cu（I） - Ptz - 3 > CAAC - Cu（I） - Ptz - 2）对构象光物理性质的影响。几何和激发态分析表明，观察到CAAC - Cu（I） - Ptz - 1、CAAC - Cu（I） - Ptz - 2和CAAC - Cu（I） - Ptz - 4构象具有相似的激发态跃迁，但它们的扭转角对能隙变化有至关重要的影响。具体而言，由于扭转跨度不同，CAAC - Cu（I） - Ptz - 2和CAAC - Cu（I） - Ptz - 3激发态之间的能量差分别为0.10和0.20 eV。值得注意的是，CAAC - Cu（I） - Ptz - 3中增大的倾斜角β降低了Cu的贡献，最低三重态（T）显示出47％的配体间电荷转移（LLCT）和28％的金属到配体电荷转移（MLCT）特征。结合最小能量交叉点（MECP）和自旋 - 轨道耦合（SOC）分析阐明了对反向系间窜越（RISC）速率的影响：证实CAAC - Cu（I） - Ptz - 3（0.41 eV MECP势垒）和CAAC - Cu（I） - Ptz - 1（SOC = 4.35 cm）抑制RISC速率（分别为1.09×10和1.09×10 s），而CAAC - Cu（I） - Ptz - 2和CAAC - Cu（I） - Ptz - 4通过降低MECP势垒和增强SOC相互作用实现了增强的RISC速率（分别为1.68×10和3.87×10 s）。这些发现突出了配体灵活性在CMA发光体光物理性质中的关键作用，为设计高效TADF材料提供了有价值的指导。
