Surface-Confined Macrocyclization via Dynamic Covalent Chemistry

On-Surface Two-Dimensional Polymerization: Advances, Challenges, and Prospects

Two-dimensional polymers (2DPs) are molecularly thin networks consisting of monomers covalently linked in at least two directions in the molecular plane. Because of the unique structural features and emergent physicochemical properties, 2DPs promise application potentials in catalysis, chemical sensing, and organic electronic devices. On-surface synthesis is of great interest to fabricate 2DPs with atomic precision, and the properties of the 2DPs can be characterized in situ through scanning probe techniques. In this Perspective, we first introduce the recent developments of on-surface 2D polymerization, including the design principle, the synthetic reactions, and the factors affecting the synthesis of 2DPs on surface. Then, we summarize some major challenges in this field, including the fabrication of high-quality 2DPs and the study of the intrinsic electronic properties of 2DPs, and we discuss some of the available solutions to address these issues.

Two-dimensional molecular networks at the solid/liquid interface and the role of alkyl chains in their building blocks

Nanoarchitectonics has attracted increasing attention owing to its potential applications in nanomachines, nanoelectronics, catalysis, and nanopatterning, which can contribute to overcoming global problems related to energy and environment, among others. However, the fabrication of ordered nanoarchitectures remains a challenge, even in two dimensions. Therefore, a deeper understanding of the self-assembly processes and substantial factors for building ordered structures is critical for tailoring flexible and desirable nanoarchitectures. Scanning tunneling microscopy is a powerful tool for revealing the molecular conformations, arrangements, and orientations of two-dimensional (2D) networks on surfaces. The fabrication of 2D assemblies involves non-covalent interactions that play a significant role in the molecular arrangement and orientation. Among the non-covalent interactions, dispersion interactions that derive from alkyl chain units are believed to be weak. However, alkyl chains play an important role in the adsorption onto substrates, as well as in the in-plane intermolecular interactions. In this review, we focus on the role of alkyl chains in the formation of ordered 2D assemblies at the solid/liquid interface. The alkyl chain effects on the 2D assemblies are introduced together with examples documented in the past decades.

Adsorptive separation using self-assembly on graphite: from nanoscale to bulk processes

Adsorptive separation is a promising lower-energy alternative for traditional industrial separation processes. While carbon-based materials have a long history in adsorptive removal of organic contaminants from solution or gas mixtures, separation using an adsorption/desorption protocol is rarely considered. The main drawbacks are the limited control in bulk adsorption experiments, as often all organic molecules are adsorbed, and lack of desorption methods to retrieve the adsorbed molecules. Using high-resolution on-surface characterization with scanning tunneling microscopy (STM), an increased understanding of the on-surface adsorption behavior under different conditions was obtained. The insight obtained from the nanoscale experiments was used to develop a highly selective separation method using adsorption and desorption on graphite, which was tested for the separation of quinonoid zwitterions. These experiments on adsorptive separation using self-assembly on graphite show its potential and demonstrate the advantage of combining surface characterization techniques with bulk experiments to exploit different possible applications of carbon-based materials.

Effects of Alkyl Chain Length on the Cold Crystallization of Schiff-Base Nickel(II) Complexes

"Cold crystallization" is the exothermic phenomenon occurring during the heating process of a supercooled liquid. Molecules that exhibit cold crystallization can be used as heat storage materials. Schiff-base nickel(II) complexes...

Carbocatalysis with pristine graphite: on-surface nanochemistry assists solution-based catalysis

Carbocatalysis holds a privileged position as a sustainable alternative to metal-based catalysis. While the focus in solution-based catalytic processes generally lies on how the heterogeneous catalyst affects the solution composition, more attention has recently been given to the analysis of the carbon material itself. Various outstanding surface characterisation techniques, efficient in assessing the catalyst on-surface composition, are now available. These include high-resolution imaging tools such as scanning tunneling microscopy (STM), capable of bringing new insights into the processes determining rate and selectivity effects induced by carbocatalysts. In this regard, the use of self-assembly on graphite as a strategy to direct the outcome of chemical reactions has already shown great potential. This promising approach gives the scientific community the exciting prospect of rationalising selectivity in carbocatalysis with pristine graphite by linking in-solution and on-surface composition.