Mechanistic Insight into the Formation of Cationic Naked Nanocrystals Generated under Equilibrium Control

详细信息    查看全文

• 作者：Sean E. Doris ; Jared J. Lynch ; Changyi Li ; Andrew W. Wills ; Jeffrey J. Urban ; Brett A. Helms
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：November 5, 2014
• 年：2014
• 卷：136
• 期：44
• 页码：15702-15710
• 全文大小：515K
• ISSN：1520-5126

文摘

Cationic naked nanocrystals (NCs) are useful building units for assembling hierarchical mesostructured materials. Until now, their preparation required strongly electrophilic reagents that irreversibly sever bonds between native organic ligands and the NC surface. Colloidal instabilities can occur during ligand stripping if exposed metal cations desorb from the surface. We hypothesized that cation desorption could be avoided were we able to stabilize the surface during ligand stripping via ion pairing. We were successful in this regard by carrying out ligand stripping under equilibrium control with Lewis acid鈥揵ase adducts of BF₃. To better understand the microscopic processes involved, we studied the reaction pathway in detail using in situ NMR experiments and electrospray ionization mass spectrometry. As predicted, we found that cationic NC surfaces are transiently stabilized post-stripping by physisorbed anionic species that arise from the reaction of BF₃ with native ligands. This stabilization allows polar dispersants to reach the NC surface before cation desorption can occur. The mechanistic insights gained in this work provide a much-needed framework for understanding the interplay between NC surface chemistry and colloidal stability. These insights enabled the preparation of stable naked NC inks of desorption-susceptible NC compositions such as PbSe, which were easily assembled into new mesostructured films and polymer-nanocrystal composites with wide-ranging technological applications.