The interaction between organic photoelectric molecules leads to the formation of a certain aggregation structure, which plays a pivotal role in the charge transport at the intermolecular interface. In view of this, we investigated the mechanism and law of intermolecular interaction by detecting the self-assembled behaviors between organic photoelectric molecules at the interface by scanning tunneling microscopy (STM). In this work, the structural transformations of tetraphenylethylene acids (H₄ETTCs) on graphite surface induced by temperature and triazine derivatives (zcy-19, zcy-27, and zcy-38 molecules) were studied by STM technology and density functional theory (DFT) calculations. At room temperature, zcy-19 and H₄ETTC molecules formed a small range of ordered co-assembled nanostructure, while for zcy-27 or zcy-38 molecules, no co-assembled nanostructures were observed and only their own self-assembled structures existed on graphite surface, individually. In the thermal annealing trials, the original co-assembled H₄ETTC/zcy-19 structure disappeared, and only zcy-19 and H₄ETTC self-assembled in separate domains. Nevertheless, new well-ordered H₄ETTC/zcy-27 or H₄ETTC/zcy-38 co-assembled structures appeared at different annealing temperatures, respectively. Combined with DFT calculations, we further analyzed the mechanism of such structural transformations by triazine derivatives and temperature. Results reveal that triazine derivatives could interact with H₄ETTC by N–H···O and O–H···N hydrogen bondings, and whether temperature or zcy series compounds could achieve successful regulation of H₄ETTC assembly behavior is closely associated with the conjugated skeleton length of zcy series compounds.

Controlling friction by the electric field is a promising way to improve the tribological performance of a variety of movable mechanical systems. In this work, the assembly structure and microscale superlubricity of a host–guest assembly are effectively controlled by the electric field. With the help of the scanning tunneling microscopy (STM) technique, the host–guest assembly structures constructed by the co-assembly of fullerene derivative (Fluorene-C₆₀) with macrocycles (4B2A and 3B2A) are explicitly characterized. Combined with density functional theory (DFT), the distinct different assembly behaviors of fullerene derivatives are revealed at different probe biases, which is attributed to the molecular polarity of the fullerene derivative. Through the control on the adsorption behavior, the friction coefficient of host–guest assembly is demonstrated to be controllable in the electric field by using atomic force microscopy (AFM). At positive probe bias, the friction coefficient of the host–guest assembly is significantly reduced and achieves superlubricity (μ_min = 0.0049). The efforts not only help us gain insight into the host–guest assembly mechanism controlled by the electric field, but also promote the further application of fullerene in micro-electro-mechanical systems (MEMS).

Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor. The morphologies, co-assembly behavior, interaction sites, and charge transfer of BTID-nF (n = 1, 2)/PC₇₁BM donor–acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), density functional theory (DFT) calculations, and transient absorption (TA) spectroscopy. The results show that BTID-1F and BTID-2F form bright strip structures, whereas BTID-nF (n = 1, 2)/PC₇₁BM form ridge-like structures with each complex composed of one BTID-nF (n = 1, 2) molecule and four PC₇₁BM molecules which adsorbed around the BTID-nF (n = 1, 2) molecule by S···π interaction. With the assistance of S···π interaction between BTID-nF (n = 1, 2) and PC₇₁BM, BTID-nF (n = 1, 2)/PC₇₁BM co-assembled ridge-like structures are more stable than the BTID-nF (n = 1, 2) ridge structures. To investigate the charge transfer of BTID-nF (n = 1, 2)/PC₇₁BM system, STS measurements, DFT calculation, and TA spectroscopy are further performed. The results show that charge transfer occurs in BTID-nF (n = 1, 2)/PC₇₁BM system with the electron transferring from BTID-nF (n = 1, 2) molecules to PC₇₁BM.

Here, the structural transformations of H₄ETTC induced by coronene (COR) and selective adsorption behaviors of COR in different templates were investigated by scanning tunnelling microscope (STM). It was discovered that the assembled architecture of H₄ETTC at the HOPG/ heptanoic acid interface depended on the concentration of COR, and the clusters of COR were obtained in the kagomé nanoporous network of H₄ETTC molecules at a high concentration of COR solution. In addition, COR clusters can also be formed in the hexagonal porous structure of hexaphenylbenzene (HPB) molecules modified by alkyl chains at the HOPG/heptanoic acid interface. When both H₄ETTC and HPB assembly structures, based on hydrogen bonding and van der Waals force respectively, were selected as the host templates, COR showed selectivity for HPB template to form HPB/COR hexagonal host–guest architecture. Density functional theory (DFT) calculations were also performed to disclose the mechanisms involved.

The two-dimensional self-assembly behaviors of tetraphenylethylene (TPE) molecules are significant for further applications, but reports are rare. The self-assembled structures of two C₂-symmetry TPE derivatives (H₄TCPE and H₄ETTC) possessing propeller structures and their stimulus responses to the addition of vinylpyridine derivatives were thoroughly studied with the assistance of scanning tunneling microscopy (STM) technique in combination with density functional theory (DFT) calculations. Although their chemical structures were similar, the H₄TCPE and H₄ETTC molecules self-assembled into closely packed lamellar and quadrilateral structures, respectively, at the 1-heptanoic acid/HOPG interface. After the addition of pyridine derivatives (DPE, PEBP-C4, and PEBP-C8), H₄TCPE and H₄ETTC showed different responsiveness resulting in different co-assembly structures. The results indicated that the structures of pyridine derivatives—including backbones and substituents—affected the intermolecular interactions of both H₄TCPE/pyridine and H₄ETTC/pyridine systems. The modification of the self-assembly behaviors of propeller-shaped H₄TCPE and H₄ETTC would contribute to the construction of more complex multilevel nanostructures.

The precise localization of organic molecules in controllable positions is an important step towards constructing functional nanostructures via the bottom-up strategy. Herein, supramolecularly organized C70-fullerene assemblies on macrocycle-modified surfaces were investigated using scanning tunneling microscopy (STM) in combination with theoretical calculations. The results revealed that an up-assembly of C70-fullerene adlayers was successfully formed on top of the bottom macrocycle arrays. Density functional theory (DFT) calculations confirmed that the macrocycle networks along with the co-adsorbed solvent 1-phenyloctane served as a selective template for trapping C70-fullerene molecules in the spectral sites and acted as a support for the C70-fullerene molecules. The periodical distribution of the C70-fullerene molecules should facilitate understanding of the strong dependence of the arrangement of C70-fullerene upon the specific interactions (apart from spatial recognition) derived from modification of the sub-monolayers.

The precise control of the conformations of biomolecules adsorbed on a surface at the single-molecule level is significant. However, it remains a huge challenge because of the complex structure and conformation diversity of biomolecules. Herein, a "nanopore-confined recognition" strategy is proposed to manipulate the adsorption of individual valinomycin molecules at room temperature through precise design of functionalized conjugated macrocycle (CPN8) supramolecular nanopores with complementary architectures and binding sites. We revealed that CPN8 prefers to selectively recognizing valinomycin with complementary architecture because of the strong synergistic interactions between the isopropyl groups of valinomycin and the amino groups of CPN8, with valinomycinhighly oriented pyrolytic graphite (HOPG) interactions. Our perspectives at the single-molecule level will provide valuable insights to improve the design of supramolecular nanopores for conformation-selective recognition of non-conjugated molecules.