Unraveling Self-Carried Chemical Feedback On Assembly Processes And The Self-Termination Of Growth In Au(I)-Thiolate Lamellae

The assembly and termination processes of Au(I)-MPA (MPA: 3-mercaptopropanionic acid) self-assembled lamellae have been studied. First, five samples of Au(I)-MPA lamellae with different termination states were prepared by changing the mixing protocols of the reactants. A self-carried chemical feedback on assembly processes was revealed by monitoring and comparing the morphological, compositional, and pH changes in each sample. It is found that the hierarchical growth from molecular species to 1D string-shaped assembly intermediates to 2D lamellae has continuously changed the molecular environments of the functional groups of carboxylic acid on the ligands and their dissociability, leading to the gradual pH rise as the assembly proceeds. The raised pH value in turn disfavors the further growth of the assemblies by increasing their surface potential. When the pH increment is not significant, consumption of intermediate assemblies can result in the termination of the products. When the pH value increment is high enough, it can kinetically prevent further growth of the lamellae due to the high surface potential. Therefore, the work discloses a brand-new mechanism for the termination of the self-assembly and provides a strategy to realize self-terminated growth in artificial self-assembly systems.