The self-assembly and pyridine regulation of a hydrogen-bonded dimeric building block formed by a low-symmetric aromatic carboxylic acid.

The supramolecular self-assembly behavior of a low-symmetric aromatic carboxylic acid molecule (H 5 BHB) and its co-assembly behavior with a series of pyridine molecules (BPD, BPDYB and TPDYB) were studied at the heptanoic acid/HOPG liquid-solid interface. Scanning tunneling microscopy (STM) observations revealed that H 5 BHB molecules tend to form dimeric building blocks which then assemble into a close-packed structure. BPD, BPDYB and TPDYB pyridine molecules were all able to form a stable two-component co-assembled structure with the H 5 BHB molecule, and in these co-assembled structures, the H 5 BHB molecule still takes the form of a dimer. It was found that the pyridine molecules were able to regulate the self-assembly structure of the H 5 BHB molecule, and the molecular arrangement of the co-assembly structures varies with the shape of the pyridine molecules. Based on the analysis of the STM results and density functional theory (DFT) calculations, the formation mechanism of the assembled structures was revealed.