On-Surface Cascade Reaction Based on Successive Debromination via Metal-Organic Coordination Template

Stepwise on-surface synthesis of nitrogen-doped porous carbon nanoribbons

Precise synthesis of carbon-based nanostructures with well-defined structural and chemical properties is of significance towards organic nanomaterials, but remains challenging. Herein, we report on a synthesis of nitrogen-doped porous carbon nanoribbons through a stepwise on-surface polymerization. Scanning tunneling microscopy revealed that the selectivity in molecular conformation, intermolecular debrominative aryl-aryl coupling and inter-chain dehydrogenative cross-coupling determined the well-defined topology and chemistry of the final products. Density functional theory calculations predict that the ribbons are semiconductors, and the band gap can be tuned by the width of the ribbons.

Improvement of bio-based polyurethane and its optimal application in controlled release fertilizer

In the past decades, polyurethane has emerged as a new material that has been widely developed and applied in coated controlled release fertilizers (CRFs). Particularly in recent years, the excessive consumption of petroleum resources and increasing demand for sustainable development have resulted in considerable interest in bio-based polyurethane coated controlled-release fertilizers. This review article focuses on the application and progress of environmentally friendly bio-based materials in the polyurethane-coated CRF industry. We also explore prospects for the green and sustainable development of coated CRFs. Using animal and plant oils, starch, lignin, and cellulose as raw materials, polyols can be produced by physical, chemical, and biological means to replace petroleum-based materials and polyurethane film coating for CRFs can be prepared. Various modifications can also improve the hydrophobicity and degradability of polyurethane film. A growing body of research on bio-based polyurethane has revealed its great potential in the production and application of coated CRFs. The purpose of this review is to highlight the practicality of bio-based materials in the application of polyurethane-coated CRFs and to clarify their current limitations.

Transformation of the coordination nanostructures of 4,4',4''-(1,3,5-triazine-2,4,6-triyl) tribenzoic acid molecules on HOPG triggered by the change in the concentration of metal ions

The modulation effects of Cu2+/Fe3+ ions on the hydrogen-bonded structure of 4,4',4''-(1,3,5-triazine-2,4,6-triyl) tribenzoic acid (TATB) on a HOPG surface have been investigated at the liquid-solid interface by scanning tunneling microscopy (STM). STM observations directly demonstrated that the self-assembled honeycomb network of TATB has been dramatically transformed after introducing CuCl2/FeCl3 with different concentrations. The metal-organic coordination structures are formed due to the incorporation of the Cu2+/Fe3+ ions. Interestingly, a Cu2+ ion remains coordinated to two COOH groups and only the number of COOH groups involved in coordination doubles when the concentration of Cu2+ ions doubled. A Fe3+ ion changes from coordination to three COOH groups to two COOH groups after increasing the concentration of Fe3+ ions in a mixed solution. Such results suggest that the self-assembled structures of TATB molecules formed by metal-ligand coordination bonds can be effectively adjusted by regulating the concentration of metal ions in a mixed solution, which has rarely been reported before. It explains that the regulatory effect of concentration leads to the diversity of molecular architectures dominated by coordination bonds.

An intermolecular hydrogen bond plays a determining role in product selection of a surface confined Schiff-base reaction

Herein, we illustrate how the cooperation of intermolecular hydrogen bonds and conformation flexibility leads to the formation of diverse complex covalent nanostructures on the surface, while the relative abundance of the final products can be further tuned by adjusting the molar ratio and concentration of monomers.

On-Surface Synthesis of Giant Conjugated Macrocycles

We have achieved an on-surface synthesis of giant conjugated macrocycles having a diameter of ≈7 nm and consisting of up to 30 subunits. The synthesis started with a debrominative coupling of the molecular precursors on a hot Ag(111) surface, leading to the formation of arched oligomeric chains and macrocycles. These products were revealed by scanning tunneling microscopy in combination with density functional theory to be covalent oligomers. These intermediates also display C-Ag organometallic bonds between parallel molecular subunits due to site-selective debromination and the asymmetric molecular conformation. Subsequent cyclodehydrogenation at higher temperatures steered the final conjugation of the macrocycles. Our findings provide a novel design strategy toward π-conjugated macrocycles and open up new opportunities for the precise synthesis of organic nanostructures.

On-Surface Self-Assembled Structural Transformation Induced by Schiff Base Reaction and Hydrogen bonds

By utilizing scanning tunneling microscopy (STM), the self-assembled nanostructures of three characteristic aldehydes have been examined at the solution-solid interface. By introducing the active reactant 5-aminoisophthalic acid (5-AIPA), we succeeded in changing the self-assembled molecular structures through the condensation reaction and obtained the information on structural transformation in real time. The corresponding carboxyl conjugated derivatives were formed in situ and developed into the closely packed and ordered molecular architectures via hydrogen bonds at the solution-solid surface. The relevant simulations have been utilized to interpret the mechanisms of forming the nanostructures. The corresponding theoretical calculation is used to explain the reaction mechanism. Compared with the traditional ways, the on-surface condensation reaction in situ could not only provide a more convenient method for regulating the self-assembled architectures but also offer a promising strategy for building functional nanostructures and devices.

Topology Selectivity in On-Surface Dehydrogenative Coupling Reaction: Dendritic Structure versus Porous Graphene Nanoribbon

Selective control on the topology of low-dimensional covalent organic nanostructures in on-surface synthesis has been challenging. Herein, with combined scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we report a successful topology-selective coupling reaction on the Cu(111) surface by tuning the thermal annealing procedure. The precursor employed is 1,3,5-tris(2-bromophenyl)benzene (TBPB), for which Ullmann coupling is impeded due to the intermolecular steric hindrance. Instead, its chemisorption on the Cu(111) substrate has triggered the ortho C-H bond activation and the following dehydrogenative coupling at room temperature (RT). In the slow annealing experimental procedure, the monomers have been preorganized by their self-assembly at RT, which enhances the formation of dendritic structures upon further annealing. However, the chaotic chirality of dimeric products (obtained at RT) and hindrance from dense molecular island make the fabrication of high-quality porous two-dimensional nanostructures difficult. In sharp contrast, direct deposition of TBPB molecules on a hot surface led to the formation of ordered porous graphene nanoribbons and nanoflakes, which is confirmed to be the energetically favorable reaction pathway through density functional theory-based thermodynamic calculations and control experiments. This work demonstrates that different thermal treatments could have a significant influence on the topology of covalent products in on-surface synthesis and presents an example of the negative effect of molecular self-assembly to the ordered covalent nanostructures.