Nine different coinage metal (Cu, Ag) π complexes of diborenes with various anionic diborene (aryl, heteroaryl) and metal substituents (Cl, Br, C₆F₅, C₂SiMe₃), stabilizing neutral donors (N-heterocyclic carbene = NHC, phosphine), configurations (cis/trans, acyclic/cyclic diborene), and charges (neutral, cationic) were synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallographic analyses. Their optical properties were investigated by UV–vis absorption and steady-state as well as time-resolved luminescence spectroscopy in solution and the solid state to gain insights into the excited-state behavior of this unusual class of photoactive compounds and to provide structure–property relationships. The structural and electronic modification of the (B═B)···M motif greatly influences not only the visible light absorption but also the photostability and quantum yields, which can reach high values of up to f = 0.42. The lifetimes are found in the nanosecond regime, providing estimated radiative rate constants over a wide range of k_r = 1.3–14 × 10⁷ s^–1, indicative of fluorescence. Intersystem crossing (ISC) is sufficiently slow for prompt emission from the S₁ state to be observed, while the spin–orbit coupling in the T₁ state is too weak for phosphorescence to occur at room temperature. ISC can be accelerated, however, by modifying diborene ligand substitution and the coinage metal center, hinting at the potential for exploiting the properties of long-lived triplet excited states of metal diborene complexes in the future.

中文翻译：

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二硼烯金属配合物的合成及荧光研究

九种不同的二硼烯金属（Cu，Ag）π配合物与各种阴离子二硼烯（芳基，杂芳基）和金属取代基（Cl，Br，C ₆ F ₅，C ₂ SiMe ₃），稳定中性供体（N-杂环卡宾= NHC，磷化氢），配置（顺式/反式，无环/环状二硼烯）和电荷（中性，阳离子）合成并通过多核NMR光谱和X射线晶体学分析表征。通过紫外-可见吸收和稳态以及溶液和固态中的时间分辨发光光谱研究它们的光学性质，以深入了解这类不寻常的光活性化合物的激发态行为并提供结构-性质关系。(B=B)···M基序的结构和电子修饰不仅极大地影响了可见光的吸收，而且极大地影响了光稳定性和量子产率，最高可达f = 0.42。寿命在纳秒范围内，提供了广泛范围内的估计辐射速率常数k _r = 1.3–14 × 10 ⁷ s ^–1，表示荧光。系间穿越 (ISC) 足够慢，可以观察到从 S _{1状态迅速发射，而 T 1}状态中的自旋轨道耦合太弱，以至于磷光在室温下无法发生。然而，通过改变二硼烯配体取代和造币金属中心可以加速 ISC，这暗示了在未来利用金属二硼烯配合物的长寿命三重激发态特性的潜力。