Host-guest dynamics in porous trimesic acid supramolecular network on graphene. Outstanding stability of the coronene guest

The post-synthetic modification of covalent organic frameworks (COFs) via host-guest chemistry is an important method to tailor their electronic properties for applications. Due to the limited structural control in the assembly of two-dimensional surface-supported COFs, supramolecular networks are traditionally used at present for host-guest experiments on surfaces, which lack structural and thermal stability, however. Here, we present a combined scanning tunneling microscopy and density functional theory study to understand the host-guest interaction in triphenylamine-based covalently-linked macrocycles and networks on Au(111). These triphenylamine-based structures feature carbonyl and hydrogen functionalized pores that create preferred adsorption sites for trimesic acid (TMA) and halogen atoms. The binding of the TMA through optimized hydrogen-bond interactions is corroborated by selective adsorption positions within the pores. Band structure calculations reveal that the strong intermolecular charge transfer through the TMA bonding reduces the band gap in the triphenylamine COFs, demonstrating the concept of supramolecular doping by host-guest interactions in surface-supported COFs. Halogen atoms selectively adsorb between two carbonyl groups at Au hollow sites. The mainly dispersive interaction of the halogens with the triphenylamine COF leads to a small downshift of the bands. Most of the halogens change their adsorption position selectively upon annealing near the desorption temperature. In conclusion, we demonstrate evidence for supramolecular doping via post-synthetic modification and to track chemical reactions in confined space.

In this work, we used the ReaxFF force field to investigate the dynamics of different network structures of trimesic acid (TMA) molecules on graphene as a function of temperature. We considered the so-called honeycomb, filled honeycomb, flower, zigzag, and close-packed TMA motifs. The thermal stability was investigated using molecular dynamics simulations with the constant number of molecules, volume, and temperature and force-biased Monte Carlo calculations up to 650 K. Our simulations provide detailed atomistic insights into the intermolecular and molecule–substrate interactions responsible for the self-assembly or the breakage of the TMA networks at different temperatures. The dynamics of hydrogen bonding were followed by counting the number of hydrogen bonds as well as by analyzing OH radial distribution functions. According to the melting temperatures obtained, the honeycomb structure has a higher stability than the high-coverage zigzag and close-packed structures. Guest TMA molecules within the pores of the honeycomb motif further increase its thermal stability, thus showing the beneficial effect of host–guest interactions. The twisting and rotation of carboxylic groups with increasing temperature are responsible for the breakage of hydrogen bonds, which ultimately leads to the melting of the networks. Partial TMA desorption observed at the onset of network disordering was attributed to the intermolecular vibrational energy transfer between the molecules. For the high-coverage close-packed network and for an island of TMA molecules with a close-packed structure, we observed a phase transition to the honeycomb structure as a consequence of the stronger dimeric −COOH bonding of the latter. The energetics of the formation of the different networks from TMA molecules in the gas phase was also investigated. Intermolecular interactions and TMA–graphene interactions have similar magnitudes. The stability of the different networks cannot be fully understood only based on energetic considerations, and in the case of the dense close-packed structure, MD simulations show how it is rapidly destabilized.

Nowadays molecular nanoporous networks have numerous uses in surface nanopatterning applications and in studies of host-guest interactions. Trimesic acid (TMA), a benzene derivative with three carboxylic groups, is a marvelous building block for forming 2D H-bonded porous networks. Here, we report a low-temperature study of the nanoporous "chicken-wire" superstructure formed by TMA molecules adsorbed on a Au(111) surface. Distinct preferential orientations of the porous networks on Au(111) lead to the formation of peculiar TMA polymorphs that are stabilized only at the boundary between rotational molecular domains. Scanning tunneling microscopy (STM) and spectroscopy are used to investigate the electronic properties of both the molecular building blocks and the pores. Sub-molecular-resolution imaging and spatially resolved electronic spectroscopy reveal a remarkable change in the appearance of the molecules in the STM images at energies in the range of the lowest unoccupied molecular orbital, accompanied by highly extended molecular wave functions into the pores. The electronic structure of the pores reflects a weak confinement of surface electrons by the TMA network. Our experimental observations are corroborated by density-functional-theory-based calculations of the nanoporous structure adsorbed on Au(111).

Herein, we report the preparation of a multifunctional metallacage-core supramolecular gel by orthogonal metal coordination and host-guest interactions. A tetragonal prismatic cage with four appended 21-crown-7 (21C7) moieties in its pillar parts was first prepared via the metal-coordination-driven self-assembly of cis-Pt(PEt3)2(OTf)2, tetraphenylethene (TPE)-based sodium benzoate ligands and linear dipyridyl ligands. Further addition of a bisammonium linker to the cage delivered a supramolecular polymer network via the host-guest interactions between the 21C7 moieties and ammonium salts, which formed a supramolecular gel at relatively higher concentrations. Due to the incorporation of a TPE derivative as the fluorophore, the gel shows emission properties. Multiple stimuli responsiveness and good self-healing properties were also observed because of the dynamic metal coordination and host-guest interactions used to stabilize the whole network structure. Moreover, the storage and loss moduli of the gel are 10-fold those of the gel without the metallacage cores, indicating that the rigid metallacage plays a significant role in enhancing the stiffness of the gel. The studies described herein not only enrich the functionalization of fluorescent metallacages via elegant ligand design but also provide a way to prepare stimuli-responsive and self-healing supramolecular gels as robust and smart materials.

Attempts to rationally tune the macroscopic mechanical performance of supramolecular hydrogel networks through noncovalent molecular interactions have led to a wide variety of supramolecular materials with desirable functions. While the viscoelastic properties are dominated by temporal hierarchy (crosslinking kinetics), direct mechanistic studies on spatiotemporal control of supramolecular hydrogel networks, based on host–guest chemistry, have not yet been established. Here, supramolecular hydrogel networks assembled from highly branched cucurbit[8]uril‐threaded polyrotaxanes (HBP‐CB[8]) and naphthyl‐functionalized hydroxyethyl cellulose (HECNp) are reported, exploiting the CB[8] host–guest complexation. Mechanically locking CB[8] host molecules onto a highly branched hydrophilic polymer backbone, through selective binary complexation with viologen derivatives, dramatically increases the solubility of CB[8]. Additionally, the branched architecture enables tuning of material dynamics of the supramolecular hydrogel networks via both topological (spatial hierarchy) and kinetic (temporal hierarchy) control. Relationship between macroscopic properties (time‐ and temperature‐dependent rheological properties, thermal stability, and reversibility), spatiotemporal hierarchy, and chain dynamics of the highly branched polyrotaxane hydrogel networks is investigated in detail. Such kind of tuning of material mechanics through spatiotemporal hierarchy improves our understanding of the challenging relationship between design of supramolecular polymeric materials and their complex viscoelasticity, and also highlights a facile strategy to engineer dynamic supramolecular materials.

Co-crystals of pyrazinamide (PZA) with terephthalic (TPH) and trimesic (TMS) acids: Structural insights and dissolution study

Spin coating is a common method for depositing very thin polymeric film across a planar surface in a short period of time. Thinning occurs due to the combined effects of centrifugal spin-off and evaporation. The evaporation of any reactive component during spinning plays an important role on the stability of spin-coated polymeric film. An investigation was carried out to study the effects of spinning on the thermal and chemical stability of the epoxy adhesive. The thermal stability of both spin-coated and without spin-coated epoxy adhesive was measured by thermogravimetric analysis (TGA) at heating rate of 10 °C/min in an inert environment. A lower thermal stability was observed for the spin-coated epoxy adhesive. At the center of the substrate it is more stable than the other locations. Thermal stability greatly deviates at the border side of the spin-coated substrate. Higher chemical stability was also observed at the center than the other locations of the spin-coated layer when immersed in the metal (nickel) etchant chemical solution. The lower thermal and chemical stability is mainly due to changes in the material properties during the spinning process. From this study it is proposed to use the reactive components that are less volatile, having higher intermolecular forces, and allow a greater part of the thinning behavior to occur without significant changes in the fluid properties during the spinning process. Lower spin speed also suggested to reduce the mechanical degradation of the polymeric adhesive for the fabrication of a polymer optical waveguide.

The outer rim of C-H bonds of coronene (COR) and hexahelicene (HEL) is similar to that of the crown conformation of [18]crown-6 (CRO), which is exploited for crystal engineering of molecular complexes of CRO. However, although CRO does form the adduct (TMA)2 x CRO x (H2O)2 (TMA = trimesic acid = 1,3,5-benzenetricarboxylic acid), its structure does not correspond to the H-bonded, three-connected honeycomb sheet architectures of (TMA)2 x COR and (TMA)2 x HEL. Instead, porous, but noninterpenetrating, H-bonded four-connected sheets are observed, with the dihydrated, crown-shaped CRO molecules functioning as spacers rather than molecular guests. In the adduct (CHTA)2 x CRO x (H2O)5 (CHTA = cis,cis-1,3,5-cyclohexanetricarboxylic acid), the tetrahydrated CRO molecules again take up the crown conformation and act as spacers, this time within porous, noninterpenetrating H-bonded three-connected sheets. The engineering goal of CRO-filled H-bonded, hexagonal honeycomb cavities similar to the COR- and HEL-filled TMA honeycomb pores in (TMA)2 x COR and (TMA)2 x HEL was met in the adduct (HIPA)6 x CRO x (H2O)10 (HIPA = 5-hydroxyisophthalic acid), crystallized from aqueous EtOH. The crystal structure of this complex is on the one hand built up of isolated hexagonal honeycomb cavities established by six HIPA molecules cyclically linked through pairwise intercarboxylic H bonds. These cavities accommodate the crown-shaped CRO molecules, oriented such that maximally straight C-H...O contacts are enabled between its 12 equatorial H atoms and the surrounding 12 carboxylic groups of HIPA, in complete analogy to the situation prevailing in (TMA)2 x HEL and (probably) (TMA)2 xCOR. The second building block of (HIPA)6 x CRO x (H2O)10 is represented by a centrosymmetric decameric water cluster, which has the connectivity of the carbon skeleton of a bishomocubane with opposite methylene bridges, in agreement with vibrational spectroscopic evidence on gaseous (H2O)10. The crystal architecture of the adduct as a whole may either be likened to a severely distorted NaCl-type lattice, with the (HIPA)6 x CRO units replacing, for example, the Na+ ions, and the water clusters substituting the Cl- ions, or else to a system of stacked host sheets set up by C-H...O bonded (HIPA)6 macrorings, which give rise to perpendicular channels taking up guest columns of alternating, H-bonded CRO and (H2O)10 units. Crystals of another, solvated HIPA-CRO adduct of the composition (HIPA)4 x CRO x (EtOH)2 were obtained from aqueous EtOH. Their crystal structure is related to those of (TMA)2 x HEL and (TMA)2 x COR inasmuch distorted HIPA honeycomb sheets are adopted, which may be developed from the hexagonal TMA sheets by replacing one third of the pairwise intercarboxylic linkages by single interphenolic H bonds. The cavities in the HIPA sheets are thus smaller than those of the TMA honeycomb sheets and elliptically shaped. The HIPA sheets associate in pairs yielding twin cavities which take up one CRO and two EtOH molecules. The CRO molecules are suspended in the twin HIPA cages through H bonds extended from the phenolic OH groups and relayed by interposed EtOH "bridges". In keeping with the elliptic shape of the pores in (HIPA)4 x CRO x (EtOH)2, the CRO molecules are not crown-shaped, but rather adopt the more rectangular form as observed in crystalline CRO itself. The crystal structure of a dihydrate of HIPA itself was analysed, too, which assembles in a complex three-dimensional H-bonded network. It is finally concluded that hydrated CRO appears to be an avid H-bond acceptor, in particular towards carboxylic acids functioning as H-bond donors.

The title compound (C9H3O6·C20H17N4)4·0.5H2O 1 was isolated from solvothermal synthesis of 4′-(4-pyridyl)-2,2′:6′,2′-terpyridine (pytpy) and trimesic acid (1,3,5-benzenetricarboxylic acid, H3BTC). It was characterized by element analysis, IR, TGA, XRD, X-ray single-crystal diffraction, and spectroscopy properties, together with quantum chemistry calculation of spectrum (UV–vis spectra) through the method b3lyp/6–31 t g (d,p) are also investigated. Single-crystal X-ray diffraction shows 1 possesses a 3-D supramolecular network with 1-D six-fold helical double chains built from protonated (H3pytpy)\(_{n}^{3+}\) cations and deprotonated (BTC)\(_{n}^{3-}\) anions. The maximum of the fluorescent emission bands of 1 is located at 427 nm (λ ex = 266 nm), with a shoulder at about 390 nm. The result of theoretic calculations confirms that 1 has small HOMO–LUMO energy gap (1.24 eV) and high chemical reactivity. The title compound (C9H3O6⋅C20H17N4)4⋅0.5H2O 1, possessing a 3-D supramolecular network with 1-D six-fold helical double chains, was isolated from solvothermal synthesis of 4′-(4-pyridyl)-2,2′:6′,2′-terpyridine (pytpy) and trimesic acid (1,3,5-benzenetricarboxylic acid, H3BTC). The result of theoretical calculations confirms that 1 has small HOMO–LUMO energy gap (1.24 eV) and high chemical reactivity.

Phenol Sulfotransferase Pharmacogenetics in Humans: Association of CommonSULT1A1Alleles with TS PST Phenotype

This work describes a trimesic acid (TMA) network formed at the open-circuit potential (OCP, ∼0.13 V) on Au(111), which we investigate with electrochemical scanning tunneling microscopy (STM). The ...

Recent advancements in encapsulation of poly aromatic hydrocarbons via macrocyclic host-guest chemistry

Supramolecular architecture, Hirshfeld surface analysis and third-order nonlinear optical properties of crown ether with 5-nitroisophthalic acid monomethyl ester and trimesic acid

Host-guest interactions are widely employed in constructing responsive materials, although less is known to manipulate the chiral property of materials using such host-guest dynamics. With the supramolecular self-assembly based on β-cyclodextrin (β-CD) and alkyl amines (CH3(CH2)n-1NH2), we report that faster host-guest dynamics induces a dipole located above the cavity of β-CD, whereas slower dynamics create in-cavity dipole. These two scenarios correspond to negative and positive chiral signals, respectively. Considering that a larger fraction of amines facilitates faster exchange between the threaded and unthreaded amines, the chiral signal for the right-handed helical ribbons can be manipulated simply by alternatively increasing the fraction of amines and β-CD. Excitingly, enzyme responsive supramolecular chirality is obtained as a result of shifting the molar ratio by enzyme triggered hydrolysis of β-CD. We expect that this strategy may open up an area of rationally designed chiral supramolecular materials based on host-guest chemistry.

Macrocycles-assembled AIE supramolecular polymer networks