Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

In this Review, we aim to provide an updated summary of the research related to hollow micro- and nanostructures, covering both their synthesis and their applications. After a brief introduction to the definition and classification of the hollow micro-/nanostructures, we discuss various synthetic strategies that can be grouped into three major categories, including hard templating, soft templating, and self-templating synthesis. For both hard and soft templating strategies, we focus on how different types of templates are generated and then used for creating hollow structures. At the end of each section, the structural and morphological control over the product is discussed. For the self-templating strategy, we survey a number of unconventional synthetic methods, such as surface-protected etching, Ostwald ripening, the Kirkendall effect, and galvanic replacement. We then discuss the unique properties and niche applications of the hollow structures in diverse fields, including micro-/nanocontainers and rea...

Synthesis, Properties, and Applications of Hollow Micro-/Nanostructures

Hollow-structured mesoporous materials (HMMs), as a kind of mesoporous material with unique morphology, have been of great interest in the past decade because of the subtle combination of the hollow architecture with the mesoporous nanostructure. Benefitting from the merits of low density, large void space, large specific surface area, and, especially, the good biocompatibility, HMMs present promising application prospects in various fields, such as adsorption and storage, confined catalysis when catalytically active species are incorporated in the core and/or shell, controlled drug release, targeted drug delivery, and simultaneous diagnosis and therapy of cancers when the surface and/or core of the HMMs are functionalized with functional ligands and/or nanoparticles, and so on. In this review, recent progress in the design, synthesis, functionalization, and applications of hollow mesoporous materials are discussed. Two main synthetic strategies, soft-templating and hard-templating routes, are broadly sorted and described in detail. Progress in the main application aspects of HMMs, such as adsorption and storage, catalysis, and biomedicine, are also discussed in detail in this article, in terms of the unique features of the combined large void space in the core and the mesoporous network in the shell. Functionalization of the core and pore/outer surfaces with functional organic groups and/or nanoparticles, and their performance, are summarized in this article. Finally, an outlook of their prospects and challenges in terms of their controlled synthesis and scaled application is presented.

Hollow‐Structured Mesoporous Materials: Chemical Synthesis, Functionalization and Applications

Surface chemistry of porphyrins and phthalocyanines

Superwetting interfacial materials have been broadly developed for extensive applications. Reversible superwetting behavior has received a great deal of attention because of the potential applications. In this paper, a hierarchical CuO coating on a stainless steel substrate was fabricated simply by a solution-immersion process at 85 °C. The as-prepared CuO-coated stainless steel surface was superhydrophilic, and obtained superhydrophobicity by modification with tetradecanoic acid for only 15 s. The modified surface converted back into superhydrophilic after being annealed in muffle furnace at 300 °C for 5 min. Moreover, the annealed surface became superhydrophobic again by remodification. A rapid reversible superwetting transition cycle was finished by modification with tetradecanoic acid and annealing treatment for only 5.25 min. When the reversible superwetting transition was applied to the CuO-coated stainless steel mesh, the resulting mesh was switchable between “oil-removing” and “water-removing” modes. Thus, the mesh was suitable for oil/water mixtures whether heavy oil or light oil is involved. After 10 cycles of the superwetting transition or separation for 10 times, the separation efficiency of both meshes remained over 99.9%. The meshes showed the stability and recyclability.

Rapid reversible superwettability transition and controllable oil/water separation based on hierarchical CuO

Host–guest self-assemblies of methyl 5-bromo-2-(hexadecyloxy)benzoate (host) and 1-bromohexadecane (guest) molecules were investigated at the liquid/solid interface by scanning tunneling microscopy. Polar solvent (1-octanoic acid) and nonpolar solvents (1-phenyloctane, n-pentadecane, n-tetradecane, and n-decane) were selected to study the solvent effect on the self-assembly of the host–guest system. It is observed that the host–guest system self-assembles into different morphologies at low concentrations due to the solvent adsorption. Only a linear structure can be obtained at high concentration in different kinds of solvents. In particular, the different self-assembled patterns obtained at low concentration will eventually transform to the same linear structure. Owing to the participation of guest molecules, a strong Br···O═C halogen bond is formed between host and guest molecules, further leading to the occurrence of physisorbed monolayers and structural transition. The density functional theory calcula...

Solvent Effect on Host–Guest Two-Dimensional Self-Assembly Mediated by Halogen Bonding

The supramolecular self-assembly of a push-pull dye is investigated using scanning tunneling microscopy (STM) at the liquid–solid interface. The molecule has an indandione head, a bithiophene backbone and a triphenylamine–bithiophene moiety functionalized with two carboxylic acid groups as a tail. The STM images show that the molecules adopt an “L” shape on the surface and form chiral Baravelle spiral triangular trimers at low solution concentrations. The assembly of these triangular chiral trimers on the graphite surface results in the formation of two types of chiral Kagome nanoarchitectures. The Kagome-α structure is composed of only one trimer enantiomer, whereas the Kagome-β structure results from the arrangement of two trimer enantiomers in a 1:1 ratio. These Kagome lattices are stabilized by intermolecular O-H···O hydrogen bonds between carboxylic acid groups. These observations reveal that the complex structure of the push-pull dye molecule leads to the formation of sophisticated two-dimensional chiral Kagome nanoarchitectures. The subsequent deposition of coronene molecules leads to the disappearance of the Kagome-β structure, whereas the Kagome-α structure acts as the host template to trap the coronene molecules. A thin film that spontaneously forms into complex geometric patterns can undergo molecular recognition interactions helpful for sensing small molecules. A team led by Xinrui Miao from the South China University of Technology in Guangzhou and Fabien Silly at the Universite Paris-Saclay in Gif sur Yvette, France, used scanning tunneling microscopy to understand how photoactive dyes commonly used in organic solar cells self-organize into assemblies. The team first modified the dyes with carboxylic acids, giving them a spiral structure and enhanced hydrogen bonding capabilities. Atomic-scale imaging of the molecules on graphite revealed that at certain concentrations, groups of dyes could lock together into triangular tiles. In turn, the tiles connected into symmetric lattices containing nanoscale pores. Certain lattices could trap aromatic hydrocarbons within their hexagonal pores. Push-pull dye molecules self-assemble into two 2D Kagome nanoarchitectures composed of a single or two chiral Baravelle spiral triangular trimer enantiomers. Only one of the two nanoarchitectures is able to trap coronene molecules.

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Molecular trapping in two-dimensional chiral organic Kagomé nanoarchitectures composed of Baravelle spiral triangle enantiomers

An ionic molecular glass based on a dendronized monoammonium salt has been facilely synthesized and utilized as an interfacial electron-injection layer in a light-emitting diode (LED). The characterization of a yellow-green LED that involves an Al cathode and a thin layer of the new compound spin cast from a methanol solution has shown device performances comparable to those obtained with a Ba/Al cathode. Photovoltaic measurements under white light irradiation reveal that a thin layer of the new compound can significantly increase the built-in potential and thus facilitate electron injection from an Al cathode. Furthermore, it is interesting to observe that the new ionic salt could undergo reorganization on the emissive conjugated polymer layer, which leads to the formation of nearly uniform nanoaggregates.

An Ionic Molecular Glass as Electron Injection Layer for Efficient Polymer Light-Emitting Diode

Our study first focus on two types of corrole dimers oxidized and reduced forms on highly oriented pyrolytic graphite (HOPG) surface. Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and contact angle measurement (CAM) were used to investigate the self-assembled monolayers of corrole dimers adsorbed on HOPG surfaces at room temperature in air. XPS and CAM results have confirmed both two molecules adsorbed on an HOPG surface and formed self-assembled films, and STM experiments found that the corrole dimers adsorbed on HOPG surfaces form similar lobes. The different stable space structure of the oxidized form molecule (OFM) and reduced form molecule (RFM), led to the diversity of the tetramer structural dimensions. The occurrence of molecular aggregations and assembly was controlled by the interactions between molecular–molecular and molecule–substrate. The electrostatic interactions between the molecules control the geometrical sizes and molecule–substrate interactions determine topographical shapes of the self-assembled corrole dimers on HOPG surface. Copyright © 2009 John Wiley & Sons, Ltd.

Wenli Deng

Papers

Rapid reversible superwettability transition and controllable oil/water separation based on hierarchical CuO

Solvent Effect on Host–Guest Two-Dimensional Self-Assembly Mediated by Halogen Bonding

Molecular trapping in two-dimensional chiral organic Kagomé nanoarchitectures composed of Baravelle spiral triangle enantiomers

An Ionic Molecular Glass as Electron Injection Layer for Efficient Polymer Light-Emitting Diode

Adsorption characteristic of self-assembled corrole dimers on HOPG