Qingdao Zeng

The formation of random tiling within a two-dimensional molecular network of the asymmetric p-terphenyl-2',3,3″,5,5″-pentacarboxylic acid (TPPC) at the heptanoic acid/highly oriented pyrolytic graphite interface was investigated using scanning tunneling microscopy and density functional theory calculations. Assemblies of TPPC formed a random tiling network with molecular cavities composed of five distinct molecular cavities. Upon introduction of coronene (COR) and pyridine derivatives (Bispy and BD), the modulation of the self-assembly process was further investigated. The structure of the TPPC/COR coassembly shows obvious concentration dependence. At low concentrations, COR molecules entered the star-shaped cavities of the TPPC network preferentially. As the concentration increased, COR occupied all cavities within the TPPC network. The introduction of pyridine derivatives (Bispy and BD) with varying backbones can completely remodel the original TPPC architecture and induce a complete structural transformation to form long-range ordered TPPC/Bispy or TPPC/BD coassembly structures. This study realizes the molecular reprogramming of hydrogen-bond networks and the controllable transition from random tiling to ordered architectures, providing a robust strategy for the precise fabrication of two-dimensional supramolecular nanostructures.

In this work, the self-assembly behaviors of tetracarboxylic acid derivatives (EBTD, BCPTD, and DETD) and their co-assembly behaviors with pyridine derivative PEBP-C8 were investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). EBTD, BCPTD, and EBTD molecules self-assembled into similar regular grid structures by forming O–H···O hydrogen bonds. Especially, with a meta-dicarboxylic group, DETD molecules could aggregate into another kind of dimeric building block, leading to more diversified self-assembly nanostructures. With the introduction of PEBP-C8, all of the O–H···O hydrogen bonds in EBTD and BCPTD systems were broken and O–H···N hydrogen bonds were formed with PEBP-C8. In contrast, for the DETD/PEBP-C8 system, partial O–H···O hydrogen bonds were retained along with the new O–H···N bonds with PEBP-C8. Both EBTD and BCPTD co-assembled with PEBP-C8 to form acid–pyridine–acid–pyridine nanostructures. Nevertheless, DETD not only assembled with PEBP-C8 into an acid–pyridine–acid–pyridine nanostructure but also formed a pyridine–acid–acid–pyridine nanostructure.

This work studied the interfacial coassembly behaviors of the aromatic acid 5',5⁗-([2,2'-bithiophene]-5,5'-diyl)bis([1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid) (H₄BDETP) with the introduced tetracarboxylic acid derivative (3',5'-bis(6-carboxynaphthalen-2-yl)-[1,1'-biphenyl]-3,5-dicarboxylic acid (BCBDA) or 5',5⁗-(ethyne-1,2-diyl)bis([1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid) (EBTD)) and coronene (COR). Intermolecular interactions and the formation mechanisms of the coassembly structures were investigated via scanning tunneling microscopy (STM) and density functional theory (DFT). H₄BDETP dimers were retained and formed hydrogen bonds with BCBDA or EBTD molecules, leading to the structural transformation of H₄BDETP into a nanoporous structure. When COR molecules were introduced into the H₄BDETP/BCBDA or H₄BDETP/EBTD binary system, COR molecules were adsorbed into suitable nanopores, and three-component host-guest structures were constructed on HOPG.

We investigate the self-assembly behaviors of the tetracarboxylic acid molecule (H₄IMD), which contains an imidazole moiety, and explore the regulation by pyridine derivatives with varying backbones and the guest molecule coronene (COR). Two H₄IMD molecules are linked through N-H···O hydrogen bonds to form a dimer, which spontaneously self-assembles into a grid structure via O-H···O hydrogen bonds. The addition of linear pyridine derivatives (BP and Bispy) can break some of the O-H···O hydrogen bonds, allowing these pyridine molecules to insert between the dimer columns. In contrast, the tripyridine derivative (TPYB) disrupts the original dimer structures, resulting in a completely altered nanostructure. Moreover, the H₄IMD self-assembled structure can be regulated into a rhombus network by the coadsorption of COR molecules. Combining scanning tunneling microscopy and density functional theory calculations, this study elucidates the diverse structural variations and the underlying mechanisms, which provide new insights into molecular coassembly.

Si lattice-based linewidth, as the most used calibrator in the semiconductor industry, failed to meet the nanoscale demands of critical dimensions (CD). In 2018, the Si{220} lattice spacing was recommended as a secondary realization of the meter definition, however, Si lattices as nanoscale rulers can only be used in ultra-high vacuum (UHV) environments. For the first time, we designed two-dimensional (2D) supramolecular self-assembly monolayers (SAMs) as a new generation of nanoscale rulers using scanning tunneling microscopy (STM) technology in atmospheric environment. Three SAMs nanoscale rulers were selected among seven types of SAMs based on their self-assembly behaviors and thermodynamic stability. One of these SAMs nanoscale rulers was used to calibrate the STM images through lattice perspective transformation method, and directly determine the lattice length along the nanoscale rulers’ lattice direction without calibration, proving the feasibility of SAMs nanoscale rulers in nanometrology. The construction of SAMs nanoscale rulers was straightforward and manageable in the atmosphere, significantly lowering the complexity of producing nano precise measurement tools. Identifying the ideal SAMs for use as nanoscale rulers holds immense potential to significantly reduce the cost of calibration in chip industries.

The 4,4-difluoro-boradiazaindacene (BODIPY) unit possesses a rigid aromatic backbone, which facilitates the formation of self-assemblies and aggregates. However, most current studies on the self-assemblies of BODIPY derivatives have relied on spectroscopic methods to indirectly gather information about the self-assembled structures. In this study, we presented three BODIPY derivatives (B-3OC₁₂, B-3OC₁₂-2I, and B-DOB-2OC₁₂) that shared the same core but were decorated with different functional groups. The self-assembled structures were revealed using scanning tunneling microscopy (STM) in combination with density functional theory (DFT). The results showed that all the molecules self-assembled into lamellar structures. When modified with three dodecyloxy chains or with the introduction of additional halogen atoms, the B-3OC₁₂ and B-3OC₁₂-2I molecules tended to distribute in a staggered form to build a tetramer or dimer. In contrast, the B-DOB-2OC₁₂ molecule, which contains a dioxaborole group, self-assembled in a head-to-tail manner. These results demonstrated that BODIPY derivatives self-assembled into different structures, depending on their distinct patterns of intermolecular interactions influenced by functional groups.

In this research, the self-assembly behaviors of two different symmetry carboxylic acid derivatives (H₃BTE and H₄BTE) regulated by solvent and guest molecule (coronene, COR) were explored at the liquid/solid interface by scanning tunneling microscopy, and the formation mechanism was investigated by density functional theory. In 1-phenyloctane, only H₃BTE molecules dissolved with extremely low concentration and self-assembled into a honeycomb structure and a new strip structure, while H₄BTE could not. In 1-heptanoic acid, H₃BTE and H₄BTE were easily dissolved, in which H₃BTE formed a regular row structure and H₄BTE formed a tetragonal structure, respectively. The host-guest interaction was investigated by introducing the COR molecules into their self-assembly structures, and due to the different symmetry, H₃BTE and H₄BTE displayed different accommodation behavior.