Xie Yi, Morgenstein Jack, Bobay Benjamin G, Song Ruyi, Caturello Naidel A M S, Sercel Peter C, Blum Volker, Mitzi David B
Thomas Lord Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, United States.
University Program in Materials Science and Engineering, Duke University, Durham, North Carolina 27708, United States.
J Am Chem Soc. 2023 Aug 16;145(32):17831-17844. doi: 10.1021/jacs.3c04832. Epub 2023 Aug 2.
Cation mixing in two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) structures represents an important degree of freedom for modifying organic templating effects and tailoring inorganic structures. However, the limited number of known cation-mixed 2D HOIP systems generally employ a 1:1 cation ratio for stabilizing the 2D perovskite structure. Here, we demonstrate a chiral-chiral mixed-cation system wherein a controlled small amount (<10%) of chiral cation S-2-MeBA (S-2-MeBA = ()-(-)-2-methylbutylammonium) can be doped into (S-BrMBA)PbI (S-BrMBA = ()-(-)-4-bromo-α-methylbenzylammonium), modulating the structural symmetry from a higher symmetry (2) to the lowest symmetry state (1). This structural change occurs when the concentration of S-2-MeBA, measured by solution nuclear magnetic resonance, exceeds a critical level─specifically, for 1.4 ± 0.6%, the structure remains as 2, whereas 3.9 ± 1.4% substitution induces the structure change to 1 (this structure is stable to ∼7% substitution). Atomic occupancy analysis suggests that one specific S-BrMBA cation site is preferentially substituted by S-2-MeBA in the unit cell. Density functional theory calculations indicate that the spin splitting along different k-paths can be modulated by cation doping. A true circular dichroism band at the exciton energy of the 3.9% doping phase shows polarity inversion and a ∼45 meV blue shift of the Cotton-effect-type line-shape relative to (S-BrMBA)PbI. A trend toward suppressed melting temperature with higher doping concentration is also noted. The chiral cation doping system and the associated doping-concentration-induced structural transition provide a material design strategy for modulating and enhancing those emergent properties that are sensitive to different types of symmetry breaking.
二维（2D）有机-无机杂化钙钛矿（HOIP）结构中的阳离子混合是修饰有机模板效应和定制无机结构的一个重要自由度。然而，已知的阳离子混合二维HOIP系统数量有限，通常采用1:1的阳离子比例来稳定二维钙钛矿结构。在此，我们展示了一种手性-手性混合阳离子体系，其中可控的少量（<10%）手性阳离子S-2-MeBA（S-2-MeBA = ()-(-)-2-甲基丁基铵）可掺杂到（S-BrMBA）PbI（S-BrMBA = ()-(-)-4-溴-α-甲基苄基铵）中，将结构对称性从较高对称性（2）调节到最低对称性状态（1）。当通过溶液核磁共振测量的S-2-MeBA浓度超过临界水平时，会发生这种结构变化 ── 具体而言，对于1.4 ± 0.6%，结构保持为2，而3.9 ± 1.4%的取代会导致结构变为1（该结构在7%的取代下稳定）。原子占有率分析表明晶胞中一个特定的S-BrMBA阳离子位点优先被S-2-MeBA取代。密度泛函理论计算表明，沿不同k路径的自旋分裂可通过阳离子掺杂进行调节。3.9%掺杂相的激子能量处的真实圆二色性带显示出极性反转，并且相对于（S-BrMBA）PbI， Cotton效应型线形有45 meV的蓝移。还注意到随着掺杂浓度升高，熔点有降低的趋势。手性阳离子掺杂体系以及相关的掺杂浓度诱导的结构转变为调节和增强那些对不同类型对称性破缺敏感的新兴特性提供了一种材料设计策略。
