Fabricating 2D Host −Guest Kagomé Packing for C₂-Symmetric Aromatic Carboxylic Acids with Different Spatial Configuration: Different Ways, Same Destination

The self-assembly of two kinds of C2-symmetric aromatic carboxylic acids named 4,4′,4″,4‴-(1,4-phenylenebis(azanetriyl))tetrabenzoic acid (H4PTA) and 5′,5″-bis(4-carboxyphenyl)-[1,1′:3′,1″:3″,1‴-quaterphenyl]-4,4‴-dicarboxylic acid (H4QDA) and the coadsorption with coronene (COR) molecules at different solution concentrations were investigated at the heptanoic acid (HA)/highly oriented pyrolytic graphite (HOPG) interface by scanning tunneling microscopy (STM). H4PTA molecules with nonplanar conformation self-assembled into a highly ordered rhombus structure at variational concentrations and subsequently could be regulated into a Kagomé network by the coadsorption of COR molecules. H4QDA molecules with planar conformation self-assembled into two various nanostructures (rhombus structure and Kagomé network) coexisting on the HOPG surface at different concentrations. The Kagomé architecture of H4QDA could act as a rigid host template to trap the COR molecules. Meanwhile, COR exhibited preferential adsorption in the porous template: COR only entered the hexagonal cavities at low concentrations and filled in all hexagonal and triangular cavities at high concentrations. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations showed that the host–guest co-assembled structures were more thermodynamically and kinetically stable. The formation of different self-assembly and co-assembly processes of two molecules could be attributed to the dissimilar molecular conformation. Our work is of significance to further explore the formation mechanism of two-dimensional (2D) porous arrangements and provides an ideal way to regulate the adsorption of porous templates.