Template-Induced Inclusion Structures with Copper(II) Phthalocyanine and Coronene as Guests in Two-Dimensional Hydrogen-Bonded Host Networks

Hydrogen-bonded two-dimensional networks of 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) were formed on the surface of highly oriented pyrolytic graphite (HOPG). With these networks as host networks and copper(II) phthalocyanine (CuPc) and coronene as guest molecules, the host−guest architectures of CuPc/TCDB and coronene/TCDB were achieved when host and guest molecules coadsorb on HOPG. The monolayer structure of the networks of TCDB and the inclusion structures of host−guest systems were investigated by STM

Selective and Competitive Adsorptions of Guest Molecules in Phase-Separated Networks

The formation of crystalline multicomponent 2D lattices, containing more than two different organic molecular building blocks, has been rarely achieved because optimized recognition and selection processes require us to achieve the targeted multicomponent surface confined patterns. In this Article, we show that tetraacidic azobenzene (NN4A) and 1,3,5-tris(10-carboxydecyloxy)-benzene (TCDB) molecules can exclusively form 2D phase-separated nanoporous networks via hydrogen bonds between carboxyl groups at the liquid–solid interface, which have two types of cavities with different size and symmetry. These networks can serve as organic templates for the accommodation of fullerene (C60), coronene, and copper(II) phthalocyanine (CuPc) molecules. The experimental and calculated results indicate that coronene can be immobilized in the cavities formed by both NN4A and TCDB, whereas CuPc can be immobilized only in the cavity formed by TCDB and C60 can be immobilized only in the cavity formed by NN4A. Moreover, in the phase-separated networks, the coronene can be preferentially immobilized in NN4A. These results could benefit the studies on highly selectively molecular recognition and separation

Photo-Induced Polymerization and Isomerization on the Surface Observed by Scanning Tunneling Microscopy

In this paper, an azobenzene derivative containing two diacetylene groups is synthesized and its self-assembly at a surface investigated using scanning tunneling microscopy (STM). Both the azo-benzene and diacetylene groups are photoactive, and the results show that surface assemblies of the targeted compound undergo polymerization following irradiation at 254 nm and reversible isomerization following alternating irradiation at 365 nm and with visible light. This is the first report of a STM investigation observing both photopolymerization and photoisomerization simultaneously for the same molecular assembly at an interface. The target molecule allows one to induce sequential and reversible structural changes to surface assemblies via multiple optical treatments, and is thus of both fundamental interest for surface science and engineering. These results provide experimental and theoretical guidance for the fabrication of future molecular optoelectronic devices

Two-Dimensional Supramolecular Self-Assembly of Stilbene Derivatives with Ester Groups: Molecular Symmetry and Alkoxy Substitution Effect

In this paper, four stilbene derivatives substituted with ester groups were synthesized and their two-dimensional (2D) self-assembled behaviors were investigated by scanning tunneling microscopy (STM) on the highly oriented pyrolytic graphite (HOPG) surface. The four target molecules are different in the symmetrical properties and the length of substituted alkoxy chains which extremely influence the self-assembly of these molecules on graphite surface. As a result, we obtained four kinds of nanostructures including chiral supramolecular networks and linear lamellae, as probed at a single molecule level

Competitive Influence of Hydrogen Bonding and van der Waals Interactions on Self-Assembled Monolayers of Stilbene-Based Carboxylic Acid Derivatives

The molecule–molecule and molecule–substrate interactions play an important role during the formation of two-dimensional (2D) supramolecular nanostructure. In this paper, the self-assembled monolayers of four stilbene derivatives possessing different chemical structures at the liquid–solid interface were investigated by employing scanning tunneling microscopy (STM). Chemical structures that affect the 2D molecular self-assembly, such as number of alkoxyl chain with carboxylic acid end-group and length of alkoxyl chain, were elucidated in detail. Systematic investigation indicated that various self-assembly structures consequently formed on highly oriented pyrolytic graphite (HOPG) surface, via a combination of intermolecular hydrogen bonding and van der Waals interactions. It is proposed that hydrogen bonding and van der Waals interactions competitively control the morphology of the monolayer, and the self-assembled 2D nanostructure is determined by balance of these two interactions

Triphenylene Substituted Pyrene Derivative: Synthesis and Single Molecule Investigation

A novel donor–acceptor material based on pyrene derivative with two substituted triphenylenes (Py-TP2) is synthesized via the Sonogashira coupling reaction. The structure and physical chemistry properties of the target molecule have been discussed, ranging from the traditional ¹H NMR and high-resolution mass spectroscopy (HRMS), over UV and PL spectra, and to the surface science research. The results revealed that the Py-TP2 molecule shows a narrowed energy gap between LUMO–HOMO and a bathochromic shift of 27 nm in the solid state as compared to that in solution, which is important for its practical applications in optoeletronic devices. Moreover, combined with DFT calculations, our STM results clearly show that the Py-TP2 molecule assembled into a stable long-ranged zigzag structure on HOPG surface. The interesting results in this contribution will boost the physical chemistry study of other functional materials under such methods