Han Jiang, Li Yawen, Zhang Peijie, Xu Bin, Xu Xiaofan, Quan Zewei
Department of Chemistry, Southern University of Science and Technology (SUSTech), Shenzhen, Guangdong 518055, China.
J Am Chem Soc. 2025 Jan 8;147(1):1291-1299. doi: 10.1021/jacs.4c15554. Epub 2024 Dec 17.
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 DMPMBr (DMP = ,'-dimethylpiperazine) HMHs of group 14 elements (M = Ge, Sn, and Pb) are developed, exhibiting pronounced stereochemical activity of s lone-pair electrons. Such 2D HMHs are chosen as a model system to demonstrate the influence of the stereochemical activity of s lone-pair electrons on the geometric configuration of inorganic units, electronic properties, and exciton emissions. The off-center distortion is introduced to describe the degree of lone-pair expression in these HMHs, and a quantitative relationship between the and FE/STE emissions is established. When the 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 s lone-pair electrons exerts a similar effect to pressure in promoting the excitonic transitions in the DMPMBr series. This study uncovers the relationship between the stereochemical activity of s lone-pair electrons and excitonic emissions, which could accelerate the development of HMHs with the desired optical properties.
孤对电子的表现受到混合金属卤化物（HMHs）中几何限制的显著影响。二维（2D）HMHs的结构维度降低，使得金属中心存在广泛的偏离中心位移。然而，二维HMHs中孤对电子诱导的偏离中心畸变对无机单元的几何构型、电子性质和激子发射的影响仍不明确。在本研究中，开发了第14族元素（M = Ge、Sn和Pb）的二维DMPMBr（DMP = ，'-二甲基哌嗪）HMHs，其s孤对电子表现出明显的立体化学活性。选择此类二维HMHs作为模型系统，以证明s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。引入偏离中心畸变来描述这些HMHs中孤对电子的表现程度，并建立了偏离中心畸变与FE/STE发射之间的定量关系。当偏离中心畸变降低到小于0.24时，单元的偏离中心畸变得到充分抑制，从而限制孤对电子的表现，有利于在压缩时激子从STE态向FE态的跃迁。用具有更多非活性s孤对电子的金属阳离子替代金属阳离子，在促进DMPMBr系列中的激子跃迁方面，产生与压力类似的效果。本研究揭示了s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性质的HMHs的开发。
