Inayeh Alex, Groome Ryan R K, Singh Ishwar, Veinot Alex J, de Lima Felipe Crasto, Miwa Roberto H, Crudden Cathleen M, McLean Alastair B
Department of Physics, Engineering Physics, and Astronomy, Queen's University, Kingston, ON, Canada.
Department of Chemistry, Queen's University, Kingston, ON, Canada.
Nat Commun. 2021 Jun 29;12(1):4034. doi: 10.1038/s41467-021-23940-0.
Although the self-assembly of organic ligands on gold has been dominated by sulfur-based ligands for decades, a new ligand class, N-heterocyclic carbenes (NHCs), has appeared as an interesting alternative. However, fundamental questions surrounding self-assembly of this new ligand remain unanswered. Herein, we describe the effect of NHC structure, surface coverage, and substrate temperature on mobility, thermal stability, NHC surface geometry, and self-assembly. Analysis of NHC adsorption and self-assembly by scanning tunneling microscopy and density functional theory have revealed the importance of NHC-surface interactions and attractive NHC-NHC interactions on NHC monolayer structures. A remarkable way these interactions manifest is the need for a threshold NHC surface coverage to produce upright, adatom-mediated adsorption motifs with low surface diffusion. NHC wingtip structure is also critical, with primary substituents leading to the formation of flat-lying NHCAu complexes, which have high mobility when isolated, but self-assemble into stable ordered lattices at higher surface concentrations. These and other studies of NHC surface chemistry will be crucial for the success of these next-generation monolayers.
尽管几十年来，金表面有机配体的自组装一直由硫基配体主导，但一类新型配体——N-杂环卡宾（NHCs），已成为一种有趣的替代选择。然而，围绕这种新型配体自组装的基本问题仍未得到解答。在此，我们描述了NHC结构、表面覆盖率和基底温度对迁移率、热稳定性、NHC表面几何结构和自组装的影响。通过扫描隧道显微镜和密度泛函理论对NHC吸附和自组装的分析表明，NHC-表面相互作用以及有吸引力的NHC-NHC相互作用对NHC单层结构具有重要意义。这些相互作用显著的一种表现方式是，需要有一个阈值NHC表面覆盖率，才能产生具有低表面扩散的直立、由吸附原子介导的吸附基序。NHC翼尖结构也很关键，主要取代基会导致形成平躺的NHCAu配合物，这些配合物单独存在时具有高迁移率，但在较高表面浓度下会自组装成稳定的有序晶格。这些以及其他关于NHC表面化学的研究，对于这些下一代单层膜的成功至关重要。
