Nagaoka Yasutaka, Schneider Jeremy, Jin Na, Cai Tong, Liu Yuzi, Wang Zhongwu, Li Ruipeng, Kim Kyung-Suk, Chen Ou
Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States.
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, United States.
J Am Chem Soc. 2024 May 15;146(19):13093-13104. doi: 10.1021/jacs.3c14603. Epub 2024 May 1.
The cluster-based body-centered-cubic superlattice (cBCC SL) represents one of the most complicated structures among reported nanocrystal assemblies, comprised of 72 truncated tetrahedral quantum dots per unit cell. Our previous report revealed that truncated tetrahedral quantum dots within cBCC SLs possessed highly controlled translational and orientational order owing to an unusual energetic landscape based on the balancing of entropic and enthalpic contributions during the assembly process. However, the cBCC SL's structural transformability and mechanical properties, uniquely originating from such complicated nanostructures, have yet to be investigated. Herein, we report that cBCC SLs can undergo dynamic transformation to face-centered-cubic SLs in response to post-assembly molecular exposure. We monitored the dynamic transformation process using in situ synchrotron-based small-angle X-ray scattering, revealing a dynamic transformation involving multiple steps underpinned by interactions between incoming molecules and TTQDs' surface ligands. Furthermore, our mechanistic study demonstrated that the precise configuration of TTQDs' ligand molecules in cBCC SLs was key to their high structural transformability and unique jelly-like soft mechanical properties. While ligand molecular configurations in nanocrystal SLs are often considered minor features, our findings emphasize their significance in controlling weak van der Waals interactions between nanocrystals within assembled SLs, leading to previously unremarked superstructural transformability and unique mechanical properties. Our findings promote a facile route toward further creation of soft materials, nanorobotics, and out-of-equilibrium assemblies based on nanocrystal building blocks.
基于团簇的体心立方超晶格（cBCC SL）是已报道的纳米晶体组装体中最复杂的结构之一，每个晶胞由72个截顶四面体量子点组成。我们之前的报告表明，cBCC SL中的截顶四面体量子点由于在组装过程中熵和焓贡献的平衡而具有不寻常的能量格局，从而具有高度可控的平移和取向有序性。然而，cBCC SL独特源于这种复杂纳米结构的结构可转换性和机械性能尚未得到研究。在此，我们报告cBCC SL可以在组装后分子暴露的情况下动态转变为面心立方SL。我们使用基于同步加速器的原位小角X射线散射监测了动态转变过程，揭示了一个涉及多个步骤的动态转变，这一转变由入射分子与TTQD表面配体之间的相互作用支撑。此外，我们的机理研究表明，cBCC SL中TTQD配体分子的精确构型是其高结构可转换性和独特的果冻状软机械性能的关键。虽然纳米晶体SL中的配体分子构型通常被认为是次要特征，但我们的研究结果强调了它们在控制组装SL内纳米晶体之间弱范德华相互作用方面的重要性，从而导致了以前未被注意到的超结构可转换性和独特的机械性能。我们的研究结果为基于纳米晶体构建块进一步创造软材料、纳米机器人和非平衡组装体提供了一条简便途径。
