Tuning Chirality of Self-Assembled PTCDA Molecules on a Au(111) Surface by Na Coordination

Chiral nanostructures are much desired in many applications, such as chiral sensing, chiroptics, chiral electronics, and asymmetric catalysis. In building chiral nanostructures, the on-surface metal-organic self-assembly is naturally suitable in obtaining atomically precise structures, but that is under the premise that there are enantioselective assembly strategies to create large-scale homochiral networks. Here, we report an approach to build chiral metal-organic networks using 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) molecules and low-cost sodium chloride (NaCl) in a controllable manner on Au(111). The chirality induction and transfer processes during network evolution with increased Na ion ratios were captured by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) methodologies. Our findings show that Na ion incorporation into achiral PTCDA molecules partially breaks intermolecular hydrogen bonds and coordinates with carboxyl oxygen atoms, which initiates a collective sliding motion of PTCDA molecules along specific directions. Consequently, "molecular columns" linked by hydrogen bonds were formed in the rearranged Na-PTCDA networks. Notably, the direction of Na ion incorporation determines the chiral characteristic by guiding the sliding direction of the molecular columns, and chirality can be transferred from Na0.5PTCDA to Na1PTCDA networks. Furthermore, our results indicate that the chirality transferring process is disrupted when intermolecular hydrogen bonds are entirely replaced by Na ions at a high Na dopant concentration. Our study provides fundamental insights into the mechanism of coordination-induced chirality in metal-organic self-assemblies and offers potential strategies for synthesizing large homochiral metal-organic networks.