Incorporation and manipulation of coronene in an organic template structure

A two-dimensional molecular template structure of 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA) was formed on a highly oriented pyrolytic graphite surface (HOPG) by self-assembly at the liquid-solid interface. Scanning tunneling microscopy (STM) investigations show high-resolution images of the porous structure on the surface. After the host structure was created, coronene molecules were inserted as guest molecules into the pores. STM results indicate that some of the guest molecules rotate inside their molecular bearing. Further investigations show that single coronene molecules can be directly kicked out of their pores by means of STM.     

Selective effect of guest molecule length and hydrogen bonding on the supramolecular host structure

A host supramolecular structure consisting of bis-(2,2':6',2' '-terpyridine)-4'-oxyhexadecane (BT-O-C16) is shown to respond to guest molecules in dramatic ways, as observed by using scanning tunneling microscopy (STM) on a highly oriented pyrolytic graphite surface under ambient conditions. It is observed that small linear molecules can be encapsulated within the host supramolecular lattice. The characteristics of the host structure were nearly unaffected by the encapsulated guest molecules of terphthalic acid (TPA) dimers, whereas appreciable changes in cavity dimension can be observed with azobenzene-4,4'-dicarboxylic acid. The STM study and density functional theory (DFT) analysis reveal that intermolecular hydrogen bonding interaction plays an essential role in forming the assembling structures. The difference in guest molecule length is considered the important cause for the different guest-host complexes.     

Giant molecular spoked wheels in giant voids: two-dimensional molecular self-assembly goes big

We present here the formation of giant pores in surface-confined molecular networks of a triangular-shaped dehydrobenzo-[12]annulene derivative: the diameter of the pores reaches over 7 nm and the giant pores are used as templates to accommodate a giant molecular spoked wheel, which allows us to observe rotational and adsorption-desorption dynamics of single guest molecules.     

Atomistic Insight Into the Host–Guest Interaction of a Photoresponsive Metal–Organic Framework

Photoresponsive functional materials have gained increasing attention due to their externally tunable properties. Molecular switches embedded in these materials enable the control of phenomena at the atomic level by light. Metal–organic frameworks (MOFs) provide a versatile platform to immobilize these photoresponsive units within defined molecular environments to optimize the intended functionality. For the application of these photoresponsive MOFs (pho-MOFs), it is crucial to understand the influence of the switching state on the host–guest interaction. Therefore, we present a detailed insight into the impact of molecular switching on the intermolecular interactions. By performing atomistic simulations, we revealed that due to different interactions of the guest molecules with the two isomeric states of an azobenzene-functionalized MOF, both the adsorption sites and the orientation of the molecules within the pores are modulated. By shedding light on the host–guest interaction, our study highlights the unique potential of pho-MOFs to tailor molecular interaction by light.     

Advances in the study of the host-guest interaction by using coronene as the guest molecule

This review supplied direct insight of host-guest molecule system by using COR as the guest molecule.     

吡啶基客体分子对枝状分子表面线状模板的选择性调节

利用扫描隧道显微术(STM)研究了枝状分子BIC3与4,4′-联吡啶(BP),吡啶乙炔撑衍生物(PE3,PE4)等分子在石墨表面的二元共组装结构.BIC3分子能够在端基为吡啶基的客体分子诱导下,形成柔性线状分子模板,并捕捉客体分子形成线状主客体结构.通过选择客体分子结构,可选择性调节BIC3主体模板结构及最终的主客体二元结构.例如,客体分子吡啶端基的间距决定BIC3-吡啶基分子主客体结构中的氢键作用方式,而客体分子侧向宽度及吡啶环的数目影响线状主客体结构的条垄间距和分子比例.研究结果为可控构筑线状主客体纳米结构,实现表面自组装结构的功能性提供了思路.     

Multicomponent Self‐Assembly with a Shape‐Persistent N‐Heterotriangulene Macrocycle on Au(111)

Multicomponent network formation by using a shape‐persistent macrocycle ( MC6 ) at the interface between an organic liquid and Au(111) surface is demonstrated. MC6 serves as a versatile building block that can be coadsorbed with a variety of organic molecules based on different types of noncovalent interactions at the liquid–solid interface. Scanning tunneling microscopy (STM) reveals the formation of crystalline bicomponent networks upon codeposition of MC6 with aromatic molecules, such as fullerene (C₆₀) and coronene. Tetracyanoquinodimethane, on the other hand, was found to induce disorder into the MC6 networks by adsorbing on the rim of the macrocycle. Immobilization of MC6 itself was studied in two different noncovalently assembled host networks. MC6 assumed a rather passive role as a guest and simply occupied the host cavities in one network, whereas it induced a structural transition in the other. Finally, the central cavity of MC6 was used to capture C₆₀ in a complex three‐component system. Precise immobilization of organic molecules at discrete locations within multicomponent networks, as demonstrated here, constitutes an important step towards bottom‐up fabrication of functional surface‐based nanostructures.     

Structural elucidation of dendritic host-guest complexes by X-ray crystallography and molecular dynamics simulations

The multiple monovalent binding of adamantyl-urea poly(propyleneimine) dendrimers with carboxylic acid-urea guests was investigated using molecular dynamics simulations and X-ray crystallography to better understand the structure and behavior of the dynamic multivalent complex in solution. The results from the two methods are consistent and suggest a preferred molecular picture of this complicated aggregate of multiple components. The guest molecules can bind to the dendrimer in a variety of ways although most involve hydrogen-bonding interactions between urea groups of the dendrimer with urea and/or carboxylic acid groups of the guest. In addition, acid-base interactions between the carboxylic acid of the guest and the tertiary amine in the interior of the dendritic host are present. Our proposed structure gives important information about the predominant dynamic interactions between the host and guest and illustrates how they fit together and interact with each other.     

Solvent induced polymorphism in supramolecular 1,3,5-benzenetribenzoic acid monolayers

This work presents a scanning tunneling microscopy (STM) based study of benzenetribenzoic acid (BTB) monolayer structures at the liquid-solid interface. On graphite(0001) the tailored molecules self-assemble into 2D supramolecular host systems, suitable for the incorporation of other nanoscopic objects. Two crystallographically different BTB structures were found-both hydrogen bonded networks. A specific structure was deliberately selected by solvent identity. One of the BTB polymorphs is a 6-fold chicken-wire structure with circular, approximately 2.8 nm wide cavities. The other structure exhibits an oblique unit cell and a different hydrogen bonding pattern. The large cavity size of the chicken-wire structure was made possible through comparatively strong 2-fold hydrogen bonds between carboxylic groups. In addition, the low conformational flexibility of BTB was supportive to combat the tendency for dense packing.     

Supramolecular self-assembly of water-soluble cavitands: investigated by molecular dynamics simulation

In this study, we have examined supramolecular self-assembly process of a hydrophobic guest with a water-soluble host known by the trivial name octa acid (OA). Two octa acids form a capsular assembly only in presence of a nonpolar guest(s). Size and shape of the guest control the stoichiometry of the capsular complex. Here, all atom molecular dynamics simulation has been utilized to investigate complex formation mechanisms of a nonpolar guest (nonylbenzene) with two OA cavitands. Nonylbenzene was encapsulated into the nonpolar cavity of OA capsule owing to solvophobic interactions. Upon encapsulation it was twisted and bent due to lack of free space within the capsule. These unusual forms obtained from the simulation study were in accord with experimental findings. The post-complexation attributes of the guest were regulated by the available free space within the OA and favorable non-covalent interactions between the guest and the walls of the OA capsule. In the identical simulation condition two OA cavitands did not form a capsule without a guest, thus indicating requirement of a guest during the self-assembly of OA cavitands.     

Molecular clusters in two-dimensional surface-confined nanoporous molecular networks: structure, rigidity, and dynamics

The self-assembly of a series of hexadehydrotribenzo[12]annulene (DBA) derivatives has been investigated by scanning tunneling microscopy (STM) at the liquid/solid interface in the absence and presence of nanographene guests. In the absence of appropriate guest molecules, DBA derivatives with short alkoxy chains form two-dimensional (2D) porous honeycomb type patterns, whereas those with long alkoxy chains form predominantly dense-packed linear type patterns. Added nanographene molecules adsorb in the pores of the existing 2D porous honeycomb type patterns or, more interestingly, they even convert the guest-free dense-packed linear-type patterns into guest-containing 2D porous honeycomb type patterns. For the DBA derivative with the longest alkoxy chains (OC20H41), the pore size, which depends on the length of the alkoxy chains, reaches 5.4 nm. Up to a maximum of six nanographene molecules can be hosted in the same cavity for the DBA derivative with the OC20H41 chains. The host matrix changes its structure in order to accommodate the adsorption of the guest clusters. This flexibility arises from the weak intermolecular interactions between interdigitating alkoxy chains holding the honeycomb structure together. Diverse dynamic processes have been observed at the level of the host matrix and the coadsorbed guest molecules.     

Locking the free-rotation of a prochiral star-shaped guest molecule inside a two-dimensional nanoporous network by introduction of chlorine atoms

Two star-shaped triazatrinaphthylene (TrisK) derivatives form highly-organized nanoporous honeycomb networks when adsorbed at the n-tetradecane/HOPG interface. STM reveals that replacing three H-atoms by three Cl-atoms in the chemical structure of the TrisK skeleton results in locking the free-rotation of the guest molecules inside the pore of the host network as a result of symmetry breaking.     

Host–Guest Complexation Using Pillar[5]arene Crystals: Crystal-Structure Dependent Uptake,Release, and Molecular Dynamics of an Alkane Guest

Host–guest complexation has been mainly investigated in solution, and it is unclear how guest molecules access the assembled structures of host and dynamics of guest molecules in the crystal state. In this study, we studied the uptake, release, and molecular dynamics of n-hexane vapor in the crystal state of pillar[5]arenes bearing different substituents. Pillar[5]arene bearing 10 ethyl groups yielded a crystal structure of herringbone-type 1:1 complexes with n-hexane, whereas pillar[5]arene with 10 allyl groups formed 1:1 complexes featuring a one-dimensional (1D) channel structure. For pillar[5]arene bearing 10 benzyl groups, one molecule of n-hexane was located in the cavity of pillar[5]arene, and another n-hexane molecule was located outside of the cavity between two pillar[5]arenes. The substituent-dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n-hexane guest. The substituent effects were not observed in host–guest chemistry in solution, and these features are unique for the crystal state host–guest chemistry of pillar[5]arenes.     

Atom-atom potential analysis of the complexing characteristics of cyclodextrins (host) with benzene and p-dihalobenzenes (guest)

Abstract

Intermolecular interaction and modelling calculations on the complexes of α-, β- and γ-cyclodextrins (host) with benzene and p-dihalobenzenes (guest) were performed. The complex formation mechanism between the host and guest molecules was evaluated from three-dimensional potential maps generated by the atom-atom potential method, and the molecular packing of the complexed compounds was visualized by a space-fill representation. Stable inclusion complexes only form when both the host and guest molecules experience a significant decrease in the complexing potential. The host and guest molecules have a maximum molecular surface contact at the minimum potential, which depends on both the cavity size and the molecular volumes of the guest molecules. The calculated interaction energies can be correlated to the association constants of complex formation determined from experiment. The molecular dynamics of the guest molecules are also discussed.     

Molecular Recognition of Chiral Zinc Porphyrin with Amino Acid Esters

One kind of novel chiral porphyrin and its zinc complex were synthesized and characterized. The molecular recognition of chiral zinc porphyrin towards amino acid esters in CHCl₃ was investigated by UV‐vis spectral titration method. The associative constants of the molecular recognition reactions were all K_D>K_L and followed the order of K(PheOMe)>K(LeuOMe)>K(ValOMe)>K(AlaOMe) in host (Zn(L‐BocTyr)TAPP). Circular dichroism spectra were used to explain chiral molecular recognition. The minimal energy conformation of host‐guest molecular system was sought by molecular dynamics method. The molecular recognition process of this host‐guest system was calculated by quantum chemistry and the results were explained by the experiments     

Relationship between Separation Behavior and Structural Flexibility in Inclusion Crystal of Cholic Acid

Selective incorporation of two aromatic compounds, benzene and ethylbenzene,into an inclusion crystal of cholic acid was investigated. Addition of an excessamount of 1:1 mixture of benzene and ethylbenzene into saturated solution ofcholic acid in 1-butanol led to a spontaneous formation of an inclusion crystal.The co-crystal contained benzene and ethylbenzene at the constant molar ratioof 8:2 irrespective of the relative concentrations of guest and host in the feedsolution, indicating that the resulting crystal consists of the two guests mixedin a single host framework. The resulting ternary crystal had thermal behaviorsimilar to a binary crystal obtained from benzene. In contrast to the guest/hostratio, the benzene/ethylbenzene ratio in the feed solution affected that in theinclusion crystal. Benzene was basically preferred in the cholic acid crystalover ethylbenzene, but the selectivity reversed at an excess amount of ethylbenzene.This separation behavior can be understood in terms of the structural flexibility ofhost frameworks.     

Self-association of rhodamine dyes in different host materials

The aggregation of rhodamine 6G in liquid crystalline solution (anisotropic host) was studied using polarised spectroscopy and in a guest-host system. The self-association of rhodamine B was investigated in molecular sieves of type AlPO(4)-5 (microporous host) using diffuse reflectance spectroscopy. Also, the molecular interaction of rhodamines in normal solvents (isotropic hosts) was studied using visible spectroscopy for comparison. Therefore, the role of the host nature in the different phases on the self-association of the guest molecules has been investigated and compared. The absorption spectrum of the rhodamine dye in liquid crystalline host is affected by a specific interaction related to the alignment by the liquid crystal property as well as solvent polarity. Due to the existence of a large amount of water molecules absorbed into channels and cavities of aluminophosphate molecular sieve, the maximum absorption wavelengths of the dye loaded AlPO(4)-5 is affected by aqueous environment of the aluminophosphate pores.     

Self-assembly of trimesic acid at the liquid-solid interface-a study of solvent-induced polymorphism

A scanning tunneling microscope operated under ambient conditions was utilized to study the self-assembly of trimesic acid (TMA) at the liquid-solid interface. On a graphite substrate, two different open, loosely packed, two-dimensional hydrogen-bond networks were found. Both structures exhibit a periodic arrangement of approximately 1.0 nm wide cavities, which can be used for the co-adsorption of another species (guest) within the cells of this host system. These two polymorphs ("chickenwire" and "flower" structures) differ in their molecular packing density and hydrogen-bonding schemes. Using a homologous series of alkanoic acids as solvents, ranging from butyric to nonanoic, selective self-assembly of either the "flower" or "chickenwire" forms was achieved on a graphite surface. Solubility of TMA in these acid solvents was found to decrease with increasing chain length, and the longer-chain solvents favored formation of the chickenwire polymorph structure on the surface.     

Construction of hydrogen-bonded ternary organic crystals derived from L-tartaric acid and their application to enantioseparation of secondary alcohols

Ternary organic crystals consisting of an L-tartaric acid-derived dicarboxylic acid, a commercially available achiral diamine, and a chiral secondary alcohol have been developed and characterized by X-ray crystallography. 1D, 2D, and 3D hydrogen-bonded supramolecular networks were constructed, depending on the structure of the diamine used. Benzylic and aliphatic secondary alcohols were enantioselectively incorporated into the crystal and were successfully enantioseparated with up to 86 and 79% enantiomeric excess (ee), respectively. Selective incorporation of one enantiomer of 2-butanol, which is a small chiral aliphatic alcohol, was achieved by the cooperative effects of hydrogen bonds, CH···π interactions, and van der Waals interactions between the guest and host molecules, with the aid of two water molecules. The high host potential of the binary supramolecular system is mainly attributed to the skewed conformation of two rigid aromatic groups of tartaric acid derivatives, which prevents dense packing of the molecules and enhances the formation of multicomponent inclusion crystals.     

Guest⊂Guest⊂Host Multicomponent Molecular Crystals: Entrapment of Guest⊂Guest in Honeycomb Networks Formed by Self‐Assembly of 1,3,5‐Tri(4‐hydroxyaryl)benzenes

Sterically‐engineered rigid trigonal molecular modules based on 1,3,5‐tri(4‐hydroxyphenyl)benzenes H1 and H2 undergo O‐H???O hydrogen‐bonded self‐assembly into eight‐fold catenated hexagonal (6,3) and two‐fold interpenetrated undulated square (4,4) networks, respectively. In the presence of [18]crown‐6 as a guest, the triphenol H1 is found to self‐assemble into a honeycomb network with hexagonal voids created between three triphenol building blocks. The guest [18]crown‐6 molecules are found to be nicely nested in hexagonal enclosures. The empty spaces within the crowns can be further filled with neutral (MeOH/water, MeOH/MeNO₂) or ionic guest species such as KI/KAcAc to furnish novel multicomponent assemblies, that is, guest ? guest ? host, that typify Russian dolls. In contrast, triphenol H2 is found to yield analogous multicomponent molecular crystals in which the guest crown–K⁺ acts as a spacers in the hydrogen‐bonded self‐assembly that leads to distorted chicken wire networks.