Study on 2D Molecular Networks of Flexible Pentacarboxylic Acid Ligands Induced by Ether Bonds in Response to Selective Guest Inclusion.

The flexibility of ligands allows for their bending, twisting, or rotation to adopt various conformations, leading to distinct symmetries during the self-assembled process. Flexible aromatic acid ligands modified by ether bonds are a promising type of self-assembled module when it comes to surfaces. Here, two pentacarboxylic acid ligands (H5L1 and H5L2) with minor skeleton differences have successfully self-assembled into disparate porous networks on the graphite surface and demonstrated excellent potential for the inclusion of guest molecules. The H5L1 molecule's network structure only accommodates coronene (COR) molecules. With fewer COR molecules, H5L1 molecules act as a host template to accommodate the COR molecules. When there are too many COR molecules, COR molecules will induce H5L1 molecules to transform into a new host-guest nanostructure. Additionally, H5L2 molecules showed the ability to capture C70 molecules and exhibited cavity selectivity. However, the assembled network of H5L2 was slightly deformed in attempts to trap the COR molecules. To understand these phenomena more deeply, various assembled mechanisms were analyzed in combination with building theoretical models and energy analysis. These results reveal the great potential of flexible aromatic acid ligands in two-dimensional self-assembly and host-guest systems for their application in related fields.