Many ligand-protected metal clusters exhibit phosphorescence at room temperature. However, strategies for improving their phosphorescence quantum yield, a critical parameter of performance, remain poorly developed. In contrast, fluorescent dyes are commonly modified by introducing heavy atoms, such as iodine (I), to enhance intersystem crossing in the excited state, thereby harnessing the heavy atom effect to increase phosphorescence efficiency. In this study, we successfully synthesized a pair of ligand-protected silver (Ag) clusters with internal cavities encapsulating anions (Xz−), namely sulfide ions (S2−) or iodide ions (I−), which significantly differ in atomic number each other. Single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy revealed that the resulting Ag clusters were composed of X@Ag54S20(thiolate)20(sulfonate)m, where (X, m) = (S, 12) or (I, 11). X-ray photoelectron spectroscopy revealed that the Ag atoms in these compounds exhibit a mixed-valence state. Furthermore, experiments on their photoluminescence revealed that a heavy central anion induced an internal heavy-atom effect similar to that observed in organic fluorescent dyes. As a result, the phosphorescence quantum yield became 16 times higher when S2− was replaced by I− as the central atom.

中文翻译：

---

重原子效应增强银簇的光致发光量子产率


许多受配体保护的金属簇在室温下表现出磷光。然而，提高其磷光量子产率（性能的关键参数）的策略仍然发展不佳。相比之下，荧光染料通常通过引入重原子（如碘 （I））来修饰，以增强激发态下的系统间交叉，从而利用重原子效应来提高磷光效率。在这项研究中，我们成功合成了一对配体保护的银 （Ag） 簇，其内部腔封装了阴离子 （Xz-），即硫化物离子 （S2-） 或碘离子 （I-），它们的原子序数彼此显着不同。单晶 X 射线衍射和核磁共振波谱显示，所得的 Ag 簇由 X@Ag54S20（硫代酸盐）20（磺酸盐）m 组成，其中 （X， m） = （S， 12） 或 （I， 11）。X 射线光电子能谱显示，这些化合物中的 Ag 原子表现出混合价态。此外，它们的光致发光实验表明，重中心阴离子诱导了类似于在有机荧光染料中观察到的内部重原子效应。结果，当 S2− 被 I− 作为中心原子取代时，磷光量子产率提高了 16 倍。