Lone-pair expression is significantly influenced by geometric constraints in hybrid metal halides (HMHs). Two-dimensional (2D) HMHs possess reduced structural dimensionality, allowing for a wide range of off-center displacement of the metal center. However, the effect of lone-pair-induced off-center distortion on the geometric configuration of inorganic units, electronic properties, and exciton emissions in 2D HMHs remains unclear. In this study, 2D DMPMBr₄ (DMP = N,N′-dimethylpiperazine) HMHs of group 14 elements (M = Ge, Sn, and Pb) are developed, exhibiting pronounced stereochemical activity of ns² lone-pair electrons. Such 2D HMHs are chosen as a model system to demonstrate the influence of the stereochemical activity of ns² lone-pair electrons on the geometric configuration of inorganic units, electronic properties, and exciton emissions. The off-center distortion D is introduced to describe the degree of lone-pair expression in these HMHs, and a quantitative relationship between the D and FE/STE emissions is established. When the D is reduced to less than 0.24, the off-center distortion of the units is sufficiently suppressed to limit the lone-pair expression, facilitating the excitonic transition from the STE state to the FE state upon compression. Substituting metal cations with those having more inactive ns² lone-pair electrons exerts a similar effect to pressure in promoting the excitonic transitions in the DMPMBr₄ series. This study uncovers the relationship between the stereochemical activity of ns² lone-pair electrons and excitonic emissions, which could accelerate the development of HMHs with the desired optical properties.

中文翻译：

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ns2 孤对表达的协同调节在杂化锗、锡和卤化铅中实现不同的激子发射


孤对电子表达受杂化金属卤化物 （HMH） 中几何约束的显著影响。二维 （2D） HMH 具有降低的结构尺寸，允许金属中心进行大范围的偏心位移。然而，孤对电子诱导的偏心畸变对 2D HMHs 中无机单元的几何构型、电子性质和激子发射的影响仍不清楚。在这项研究中，开发了第 14 族元素（M = Ge、Sn 和 Pb）的 2D DMPMBr₄ （DMP = N，N′-二甲基哌嗪） HMH，表现出 ns² 个孤对电子的显着立体化学活性。选择这种 2D HMH 作为模型系统，以证明 ns² 孤对电子的立体化学活性对无机单元的几何构型、电子性质和激子发射的影响。引入偏心畸变 D 来描述这些 HMH 中孤对电子的表达程度，并建立了 D 和 FE/STE 发射之间的定量关系。当 D 减小到 0.24 以下时，单元的偏心失真被充分抑制以限制孤对电子表达，从而促进压缩时从 STE 状态到 FE 状态的激子转变。用具有更多非活性 ns² 孤对电子的阳离子取代金属阳离子，在促进 DMPMBr₄ 系列中的激子跃迁方面发挥与压力类似的作用。 本研究揭示了 ns² 个孤对电子的立体化学活性与激子发射之间的关系，这可能会加速具有所需光学特性的 HMH 的开发。