Functionalizing hydrogen-bonded surface networks with self-assembled monolayers

Voltage-Gated Switching of Moiré Patterns in Epitaxial Molecular Crystals

Studying molecular materials at the nanoscale allows us to gain a deeper understanding of supramolecular structure formation and serves as the basis for rationally controlling the resulting interfacial properties. Here, we describe the formation of extended Moiré patterns resulting from the assembly of dipolar π-conjugated molecules on highly oriented pyrolytic graphite at the liquid-solid interface as characterized by scanning tunneling microscopy (STM). By switching the bias of the sample and thus the orientation of the external electric field in the vicinity of the STM junction, structural reorganization of the molecular building blocks and the resulting organic 2D crystal is induced and can conveniently be monitored in situ by the appearance and disappearance of the Moiré patterns. Importantly, the formation and loss of the Moiré patterns are fully reversible, providing exquisite control over epitaxial molecular crystals. Our approach provides fundamental insights into the supramolecular organization and resulting superstructure formation of incommensurable 2D lattices upon applying an electric field and enables the rational tuning of Moiré patterns as a key step toward the potential integration of organic 2D crystals in molecular nanodevices.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Characterize and Mediate Assembly of Triptycenes on Au(111) Surface

Herein, we report the assembly behavior of triptycenes with aldehyde (Trip-1) and amino (Trip-2) groups on pristine and iodine-passivated Au(111) surfaces by a combination of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and density functional theory (DFT) calculation. On Au(111) surface, Trip-1 forms long trimer chains and two-dimensional islands via aldehyde-aldehyde hydrogen bonding in one dimension and π-π stacking of adjacent benzene rings in the other dimension. In contrast, Trip-2 lies as individuals or in disorderly stacked islands. Trip-2 and Trip-1 can be mixed in an arbitrary ratio. And Trip-2 molecules disrupt the ordered self-assembly structure of Trip-1 due to the formation of stronger aldehyde-amino hydrogen bonding. DFT, XPS, and Raman spectra confirm the conformational difference of Trip-1 and -2, as well as the aldehyde-amino hydrogen bonding formation in Trip-1 and Trip-2 mixture. On the iodine-passivated Au(111) surface, Trip-1 forms single-molecule chains and a hexagonal closely packed structure due to iodine interlayer mediation. Trip-2 molecules disrupt the hexagonal closely packed structure of Trip-1.

Self-Assembly of Molecular Landers Equipped with Functional Moieties on the Surface: A Mini Review

The bottom-up fabrication of supramolecular and self-assembly on various substrates has become an extremely relevant goal to achieve prospects in the development of nanodevices for electronic circuitry or sensors. One of the branches of this field is the self-assembly of functional molecular components driven through non-covalent interactions on the surfaces, such as van der Waals (vdW) interactions, hydrogen bonding (HB), electrostatic interactions, etc., allowing the controlled design of nanostructures that can satisfy the requirements of nanoengineering concepts. In this context, non-covalent interactions present opportunities that have been previously explored in several molecular systems adsorbed on surfaces, primarily due to their highly directional nature which facilitates the formation of well-ordered structures. Herein, we review a series of research works by combining STM (scanning tunneling microscopy) with theoretical calculations, to reveal the processes used in the area of self-assembly driven by molecule Landers equipped with functional groups on the metallic surfaces. Combining these processes is necessary for researchers to advance the self-assembly of supramolecular architectures driven by multiple non-covalent interactions on solid surfaces.

Supramolecular polynuclear clusters sustained cubic hydrogen bonded frameworks with octahedral cages for reversible photochromism

Developing supramolecular porous crystalline frameworks with tailor-made architectures from advanced secondary building units (SBUs) remains a pivotal challenge in reticular chemistry. Particularly for hydrogen-bonded organic frameworks (HOFs), construction of geometrical cavities through secondary units has been rarely achieved. Herein, a body-centered cubic HOF (TCA_NH4) with octahedral cages was constructed by a C3-symmetric building block and NH4+ node-assembled cluster (NH4)4(COOH)8(H2O)2 that served as supramolecular secondary building units (SSBUs), akin to the polynuclear SBUs in reticular chemistry. Specifically, the octahedral cages could encapsulate four homogenous haloforms including CHCl3, CHBr3, and CHI3 with truncated octahedron configuration. Crystallographic evidence revealed the cages served as spatially-confined nanoreactors, enabling fast, broadband photochromic effect associated with the reversible photo/thermal transformation between encapsulated CHI3 and I2. Overall, this work provides a strategy by shaping SSBUs to expand the framework topology of HOFs and a prototype of hydrogen-bonded nanoreactors to accommodate reversible photochromic reactions.

Rapid Semiconducting Supramolecular Mg(II)-Metallohydrogel: Exploring Its Potential in Nonvolatile Resistive Switching Applications and Antiseptic Wound Healing Properties

An effective strategy was employed for the rapid development of a supramolecular metallohydrogel of Mg(II) ion (i.e., Mg@PEHA) using pentaethylenehexamine (PEHA) as a low-molecular-weight gelator in aqueous medium under ambient conditions. The mechanical stability of the synthesized Mg@PEHA metallohydrogel was characterized by using rheological analysis, which showed its robustness across different angular frequencies and oscillator stress levels. The metallohydrogel exhibited excellent thixotropic behavior, which signifies that Mg@PEHA has a self-healing nature. Field emission scanning electron microscopy and transmission electron microscopy images were utilized to explore the rectangular pebble-like hierarchical network of the Mg@PEHA metallohydrogel. Elemental mapping through energy-dispersive X-ray spectroscopy analysis confirmed the presence of primary chemical constituents in the metallohydrogel. Fourier transform infrared spectroscopy spectroscopy provided insights into the possible formation strategy of the metallohydrogel. In this work, Schottky diode structures in a metal-semiconductor-metal geometry based on a magnesium(II) metallohydrogel (Mg@PEHA) were constructed, and the charge transport behavior was observed. Additionally, a resistive random access memory (RRAM) device was developed using Mg@PEHA, which displayed bipolar resistive switching behavior at room temperature. The researchers investigated the switching mechanism, which involved the formation or rupture of conduction filaments, to gain insights into the resistive switching process. The RRAM device demonstrated excellent performance with a high ON/OFF ratio of approximately 100 and remarkable endurance of over 5000 switching cycles. RRAM devices exhibit good endurance, meaning they can endure a large number of read and write cycles without significant degradation in performance. RRAM devices have shown promising reliability in terms of long-term performance and stability, making them suitable for critical applications that require reliable memory solutions. Significant inhibitory activity against the drug-resistant Klebsiella pneumonia strain and its biofilm formation ability was demonstrated by Mg@PEHA. The minimum inhibitory concentration value of the metallohydrogel was determined to be 3 mg/mL when it was dissolved in 1% DMSO. To study the antibiofilm activity, an MTT assay was performed, revealing that biofilm inhibition (60%) commenced at 1 mg/mL of Mg@PEHA when dissolved in 1% DMSO. Moreover, in the mouse excisional wound model, Mg@PEHA played a crucial role in preventing postoperative wound infections and promoting wound healing.

Influence of Temperature-Guided SAM Growth on Wetting and Its Mass Transfer Models

The formation and growth of self-assembled monolayers (SAMs) composed of amphiphiles have garnered significant attention due to their diverse technical applications. This article reports the findings of molecular dynamics simulations aimed at elucidating the intricate relationship between the wetting behavior of amphiphiles, specifically n-alkanols, and the growth of their SAMs on a mica surface under varying temperature conditions. The investigation quantifies the structural characteristics of the formed SAMs, including density profiles, in-plane radial distribution functions, order parameters, and end-to-end length distributions of n-alkanol molecules within the SAM. Thermodynamic properties, such as the second virial coefficient and excess entropy, are examined in relation to temperature and time. The growth of the SAM is assessed by analyzing characteristic time scales at different temperatures and in-plane diffusion of n-alkanol molecules and utilizing classical theories of mass transfer to quantify the growth rate as a function of temperature. These results are then correlated with changes in the contact angle and spreading coefficient of n-alkanol droplets on the mica surface over time, providing insights into the impact of SAM growth on the wetting behavior and the mass transfer model of such systems.

Toward Two-Dimensional Tessellation through Halogen Bonding between Molecules and On-Surface-Synthesized Covalent Multimers

The ability to engineer sophisticated two-dimensional tessellation organic nanoarchitectures based on triangular molecules and on-surface-synthesized covalent multimers is investigated using scanning tunneling microscopy. 1,3,5-Tris(3,5-dibromophenyl)benzene molecules are deposited on high-temperature Au(111) surfaces to trigger Ullmann coupling. The self-assembly into a semi-regular rhombitrihexagonal tiling superstructure not only depends on the synthesis of the required covalent building blocks but also depends on their ratio. The organic tessellation nanoarchitecture is achieved when the molecules are deposited on a Au(111) surface at 145 °C. This halogen-bonded structure is composed of triangular domains of intact molecules separated by rectangular rows of covalent dimers. The nearly hexagonal vertices are composed of covalent multimers. The experimental observations reveal that the perfect semi-regular rhombitrihexagonal tiling cannot be engineered because it requires, in addition to the dimers and intact molecules, the synthesis of covalent hexagons. This building block is only observed above 165 °C and does not coexist with the other required organic buildings blocks.

Selective Self-Assembly and Modification of Herringbone Reconstructions at a Solid-Liquid Interface of Au(111)

The precise control of molecular self-assembly on surfaces presents many opportunities for the creation of complex nanostructures. Within this endeavor, selective patterning by exploiting molecular interactions at the solid-liquid interface would be a beneficial capability. Using scanning tunneling microscopy at the 1,2,4-trichlorobenzene/Au(111) interface, we observed selective self-assembly of 1,3,5-tris(4-methoxyphenyl)benzene (TMPB) molecules in the face-centered cubic (FCC) regions of Au(111). Density functional theory calculations suggest higher adsorption energy of TMPB molecules at FCC regions, explaining the preference for self-assembly. The molecular coverage is found to increase with the concentration of the applied solution, eventually yielding a full monolayer. Moreover, the adsorption of TMPB molecules induces a concentration-dependent lifting of the herringbone reconstruction, observed as an increase in the area of the FCC regions at higher concentrations. Our results represent a simple and cost-effective selective nanoscale patterning method on Au(111), providing a possible avenue to guide the co-adsorption of other functional molecules.

Surface supramolecular assemblies tailored by chemical/physical and synergistic stimuli: a scanning tunneling microscopy study

Supramolecular self-assemblies formed by various non-covalent interactions can produce diverse functional networks on solid surfaces. These networks have recently attracted much interest from both fundamental and application points of view. Unlike covalent organic frameworks (COFs), the properties of the assemblies differ from each other depending on the constituent motifs. These various motifs may find diverse applications such as in crystal engineering, surface modification, and molecular electronics. Significantly, these interactions between/among the molecular tectonics are relatively weak and reversible, which makes them responsive to external stimuli. Moreover, for a liquid-solid-interface environment, the dynamic processes are amenable to in situ observation using scanning tunneling microscopy (STM). In the literature, most review articles focus on supramolecular self-assembly interactions. This review summarizes the recent literature in which stimulation sources, including chemical, physical, and their combined stimuli, cooperatively tailor supramolecular assemblies on surfaces. The appropriate design and synthesis of functional molecules that can be integrated on different surfaces permits the use of nanostructured materials and devices for bottom-up nanotechnology. Finally, we discuss synergic effect on materials science.

A novel supramolecular Zn(ii)-metallogel: an efficient microelectronic semiconducting device application

A unique strategy for the synthesis of a supramolecular metallogel employing zinc ions and adipic acid in DMF medium has been established at room temperature. Rheological analysis was used to investigate the mechanical characteristics of the supramolecular Zn(ii)-metallogel. Field emission scanning electron microscopy and transmission electron microscopy were used to analyse the hexagonal shape morphological features of the Zn(ii)-metallogel. Interestingly, the electrical conductivity is observed in the electronic device with Zn(ii)-metallogel based metal-semiconductor (MS) junctions. All aspects of the metallogel's electrical properties were investigated. The electrical conductivity of the metallogel-based thin film device was 7.38 × 10-5 S m-1. The synthesised Zn(ii)-metallogel based device was investigated for its semi-conductive properties, such as its Schottky barrier diode nature.

Assembly of Sn(IV)-Porphyrin Cation Exhibiting Supramolecular Interactions of Anion···Anion and Anion···π Systems

Trans-diaqua[meso-tetrakis(4-pyridyl)porphyrinato]Sn(IV) dinitrate complexes were assembled in a two-dimensional manner via hydrogen bonding between aqua ligands and pyridyl substituents. Interestingly, this supramolecular assembly was accompanied by unconventional noncovalent interactions, such as anion···anion and anion···π interactions, which were confirmed by X-ray crystallographic analysis. Two nitrate anions close to 2.070 Å were constrained in a confined space surrounded by four hydrogen-bonded Sn(IV)-porphyrin cations. The nitrate anion was also 3.433 Å away from the adjacent pyrrole ring, and the dihedral angle between the two mean planes was estimated to be 7.39°. The preference of the anion···π interaction was related to the electron-deficient π-system owing to the high-valent Sn(IV) center and cationic nature of the porphyrin complex. These two unconventional noncovalent interactions played an important role in the formation of a one-dimensional array with pairs of Sn(IV)-porphyrin cation and nitrate anion.

Differences in perchlorate adsorption to azobenzene monolayers on gold formed from thioacetate and thiol precursors

Modification of metal surfaces with complex molecules opens interesting opportunities to build additional functionality into these surfaces. In this work, self assembled monolayers (SAMs) based on the same photoswitchable azobenzene motif but with different head groups have been synthesized and their SAMs on Au(111)/Si substrates have been characterized. 3-[(4-phenylazo)phenoxy]propyl thiol (PAPT) and its acetyl group protected analog, 3-[(4-phenylazo)phenoxy]propyl thioacetate (PAPA), have been synthesized. SAMs from PAPT and PAPA have been characterized by infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ellipsometry and cyclic voltammetry (CV). The SAM-forming units of both SAMs are the same, as confirmed by IR and XPS, and the SAMs have similar surface coverage, as evidenced by analysis of the reductive desorption peaks in CVs. The tilt angle of the azobenzene moiety was ca. 75° with respect to the surface normal as determined by IR spectroscopy, i.e., the molecules are lying quite flat on the gold surface. Despite similar surface coverages, the CVs for PAPT in aqueous perchlorate solution show a typical perchlorate adsorption peak to gold, whereas the corresponding experiments with PAPA show no perchlorate adsorption at all. In conclusion, SAM formation can lead to an increase in the number of electrochemically accessible surface sites on the final, SAM covered surface. Whether the amount of such sites increases or decreases, depends on the precursor. The precursor most likely affects the adsorption mechanism and thus the atomic surface structure of the metal at the metal/SAM interface. Thus, details of the SAM formation mechanism, which is affected by the precursor used, can have quite strong effects on the electrochemical properties, and likely also electrocatalytic properties, of the resulting modified surface.

Molecular planting of a single organothiol into a "gap-site" of a 2D patterned adlayer in an electrochemical environment

The self-assembled inclusion of molecules into two-dimensional (2D) porous networks on surfaces has been extensively studied because 2D functional materials consisting of organic molecules have become an important research topic. However, the isolation of a single molecular thiol remains a challenging goal. Here, we report a method of planting and isolating organothiols onto a 2D patterned organic adlayer at an electrochemical interface. In situ scanning tunneling microscopy revealed that the phase transition of an ovalene adlayer is electrochemically induced and that the gap site created by three ovalene molecules serves as a 2D molecular template to isolate thiol molecules and to standardize the distance between them via the formation of precise selective open spaces, suggesting that electrochemical "molecular planting" opens applications for 2D patterns of isolated single organothiol molecules.

Thermally Stable Array of Discrete C60s on a Two-Dimensional Crystalline Adlayer of Macrocycles both in Vacuo and under Ambient Pressure

A periodic monolayer array of discrete C₆₀s was generated on an atomically flat Au(111) surface with the aid of a template adlayer. The template was a two-dimensional (2D) array of molecular pits prepared on an Au(111) surface through 2D crystallization of shape-persistent macrocycles composed of four carbazole and four salphens/Ni-salphens with a 1 nm hollow. Scanning tunneling microscopy imaging under ultra-high vacuum revealed that the square-shaped macrocycles, with 1.5 nm sides, were arranged with a periodic spacing of approximately 4.0 nm on the Au(111) surface, where the orientation and periodicity of the macrocycles were dependent on their chemical structures. After sublimation of C₆₀s onto the adlayer, a single C₆₀ molecule was entrapped in each pit, and an ordered molecular array of C₆₀s was attained with a pattern similar to that of the macrocycles. The periodic pattern of C₆₀s on the surface was thermally stable up to approximately 200 °C, even under ambient pressure. Scanning tunneling spectroscopy suggested the existence of an electronic interaction between the C₆₀s and the Au(111) surface that was influenced by the macrocycle template on the surface.

Coronene and Phthalocyanine Trapping Efficiency of a Two-Dimensional Kagomé Host-Nanoarchitecture

The trapping of coronene and zinc phthalocyanine (ZnPc) molecules at low concentration by a two-dimensional self-assembled nanoarchitecture of a push–pull dye is investigated using scanning tunneling microscopy (STM) at the liquid–solid interface. The push–pull molecules adopt an L-shaped conformation and self-assemble on a graphite surface into a hydrogen-bonded Kagomé network with porous hexagonal cavities. This porous host-structure is used to trap coronene and ZnPc guest molecules. STM images reveal that only 11% of the Kagomé network cavities are filled with coronene molecules. In addition, these guest molecules are not locked in the host-network and are desorbing from the surface. In contrast, STM results reveal that the occupancy of the Kagomé cavities by ZnPc evolves linearly with time until 95% are occupied and that the host structure cavities are all occupied after few hours.

A Solid Transformation into Carboxyl Dimers Based on a Robust Hydrogen-Bonded Organic Framework for Propyne/Propylene Separation

Self-assembly of N,N,N',N'-tetrakis(4-carboxyphenyl)-1,4-phenylenediamine with the help of different solvents provides isostructural hydrogen-bonded organic frameworks (HOF-30). Single-crystal X-ray diffraction (SCXRD) analysis reveals HOF-30 possesses 3D ten-fold interpenetrated dia nets connected by two kinds of hydrogen bonds, namely solvent-bridged carboxyl dimers and carboxyl⋅⋅⋅carboxyl dimers. Degassing treatment for HOF-30 yields HOF-30a with 3D ten-fold interpenetrated dia nets but linked with sole carboxyl⋅⋅⋅carboxyl dimers. Reversible hydrogen-bond-to-hydrogen-bond transformation between solvent-bridged carboxyl dimers in HOF-30 and carboxyl⋅⋅⋅carboxyl dimers in HOF-30a has been unveiled by single-crystal and powder X-ray diffraction. In addition, HOF-30a enables the selective adsorption of propyne over propylene according to single-component sorption and breakthrough experiments. The preferred propyne location in HOF has also been identified by SCXRD test.

Porous Honeycomb Self-Assembled Monolayers: Tripodal Adsorption and Hidden Chirality of Carboxylate Anchored Triptycenes on Ag

Molecules with tripodal anchoring to substrates represent a versatile platform for the fabrication of robust self-assembled monolayers (SAMs), complementing the conventional monopodal approach. In this context, we studied the adsorption of 1,8,13-tricarboxytriptycene (Trip-CA) on Ag(111), mimicked by a bilayer of silver atoms underpotentially deposited on Au. While tripodal SAMs frequently suffer from poor structural quality and inhomogeneous bonding configurations, the triptycene scaffold featuring three carboxylic acid anchoring groups yields highly crystalline SAM structures. A pronounced polymorphism is observed, with the formation of distinctly different structures depending on preparation conditions. Besides hexagonal molecular arrangements, the occurrence of a honeycomb structure is particularly intriguing as such an open structure is unusual for SAMs consisting of upright-standing molecules. Advanced spectroscopic tools reveal an equivalent bonding of all carboxylic acid anchoring groups. Notably, density functional theory calculations predict a chiral arrangement of the molecules in the honeycomb network, which, surprisingly, is not apparent in experimental scanning tunneling microscopy (STM) images. This seeming discrepancy between theory and experiment can be resolved by considering the details of the actual electronic structure of the adsorbate layer. The presented results represent an exemplary showcase for the intricacy of interpreting STM images of complex molecular films. They are also further evidence for the potential of triptycenes as basic building blocks for generating well-defined layers with unusual structural motifs.

Surface self-assembly involving the interaction between S and N atoms

Regulation of the self-assembly nanostructures by recruiting the electrostatic interaction between S and N atoms.

Perylenetetracarboxylic Diimide as Diffusion-Less Electrode Material for High-Rate Organic Na-Ion Batteries

In this work 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) is investigated as electrode material for organic Na-ion batteries. Since PTCDI is a widely used industrial pigment, it may turn out to be a cost-effective, abundant, and environmentally benign cathode material for secondary Na-ion batteries. Among other carbonyl pigments, PTCDI is especially interesting due to its high Na-storage capacity in combination with remarkable high rate capabilities. The detailed analysis of cyclic voltammetry measurements reveals a diffusion-less mechanism, suggesting that Na-ion storage in the PTCDI film allows for exceptionally fast charging/discharging rates. This finding is further corroborated by galvanostatic sodiation measurements at high rates of 17 C (2.3 A g-1 ), showing that 57 % of the theoretically possible capacity of PTCDI, or 78 mAh g-1 , are attained in only 3.5 min charging time.

Dynamic Supramolecular Template: Multiple Stimuli-Controlled Size Adjustment of Porous Networks

Dynamically switchable porous networks offer exciting potential in functionalizing surfaces. The structure and morphology of the networks can be controlled by applying external stimuli. Here, a dynamic supramolecular template assembled by 1,3,5-tris(4-carboxyphenyl)benzene (BTB) is successfully achieved at the liquid-solid interface by applying two external stimuli simultaneously. Upon varying the concentration of BTB solution together with switching the polarity of the sample bias, self-assembled monolayers (SAMs) undergo phase transitions twice: an immediate transition from a compact structure to a macroporous (honeycomb) structure as a response to the change in the electric field and a fast-changing transition from the macroporous to a microporous (oblique) structure. With saturated BTB solution, however, the initial compact structure can only transform into the oblique structure after switching the polarity of the sample bias without the appearance of a honeycomb structure. The different phase transitions suggest that the dynamic supramolecular template can only survive at a specific concentration range and is obtainable by performing multiple stimuli simultaneously. Interestingly, introducing a guest molecule to the system can adjust the phase transition process and effectively stabilize the honeycomb structure of BTB. The flexibility associated with the porous networks renders it a dynamic supramolecular template for guest binding.

Two-Dimensional Hydrogen-Bonded Nanoarchitecture Composed of Rectangular 3,4,9,10-Perylenetetracarboxylic Diimide and Boomerang-Shaped Molecules Resulting from the Dissociation of 1,3,5-Tris(4-aminophenyl)benzene

The self-assembly of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) with the star-shaped 1,3,5-tris(4-aminophenyl)benzene (TAPB) on Au(111) is investigated using scanning tunneling microscopy. PTCDI forms a compact canted arrangement on the gold surface. When TAPB is sublimated at a high temperature, the molecule dissociates into a 4-aminophenyl group and a boomerang-shaped compound. The boomerang molecule self-assembles with PTCDI to create a two-dimensional (2D) nanoarchitecture stabilized by N-H···O-C hydrogen bonds between the dissociated TAPB and PTCDI. The molecular ratio of this multicomponent structure is 1:1.

N-Heterocyclic carbene and thiol micropatterns enable the selective deposition and transfer of copper films

Microcontact printed patterns of N-heterocyclic carbenes (NHCs) and thiols were prepared on gold substrates and utilized as templates for the creation of metallic Cu structures using electroplating. The presence of the NHC in the pattern is essential to enable the transfer of the resulting copper microstructures to a second substrate.

Self-assembly of core-corona particles confined in a circular box

Using Monte Carlo simulations, we study the assembly of colloidal particles interacting via isotropic core-corona potentials in two dimensions and confined in a circular box. We explore the structural variety at low temperatures as function of the number of particles (N) and the size of the confining box and find a rich variety of patterns that are not observed in unconfined flat space. For a small number of particles [Formula: see text], we identify the zero-temperature minimal energy configurations at a given box size. When the number of particles is large ([Formula: see text]), we distinguish different regimes that appear in route towards close packing configurations as the box size decreases. These regimes are characterized by the increase in the number of branching points and their coordination number. Interestingly, we obtain anisotropic open structures with unexpected variety of rotational symmetries that can be controlled by changing the model parameters, and some of the structures have chirality, in spite of the isotropy of the interactions and of the confining box. For arbitrary temperatures, we employ Monte Carlo integration to obtain the average energy and the configurational entropy of the system, which are then used to construct a phase diagram as function of temperature and box radius. Our findings show that confined core-corona particles can be a suitable system to engineer particles with highly complex internal structure that may serve as building blocks in hierarchical assembly.

Edge Phonon Excitations in a Chiral Self-Assembled Supramolecular Nanoribbon

By design, coupled mechanical oscillators offer a playground for the study of crystalline topology and related properties. Particularly, non-centrosymmetric, supramolecular nanocrystals feature a complex phonon spectrum where edge modes may evolve. Here we show, employing classical atomistic calculations, that the edges of a chiral supramolecular nanoribbon can host defined edge phonon states. We suggest that the topology of several edge modes in the phonon spectrum is nontrivial and thermally insulated from bulk states. By means of molecular dynamics, we excite a supramolecular bond to launch a directional excitation along the edge without considerable bulk or back-propagation. Our results suggest that supramolecular monolayers can be employed to engineer phonon states that are robust against backscattering, toward supramolecular thermal waveguides, diodes, and logics.

Graphite and Graphene Fairy Circles: A Bottom-Up Approach for the Formation of Nanocorrals

A convenient covalent functionalization approach and nanopatterning method of graphite and graphene is developed. In contrast to expectations, electrochemically activated dediazotization of a mixture of two aryl diazonium compounds in aqueous media leads to a spatially inhomogeneous functionalization of graphitic surfaces, creating covalently modified surfaces with quasi-uniform spaced islands of pristine graphite or graphene, coined nanocorrals. Cyclic voltammetry and chronoamperometry approaches are compared. The average diameter (45-130 nm) and surface density (20-125 corrals/μm²) of these nanocorrals are tunable. These chemically modified nanostructured graphitic (CMNG) surfaces are characterized by atomic force microscopy, scanning tunneling microscopy, Raman spectroscopy and microscopy, and X-ray photoelectron spectroscopy. Mechanisms leading to the formation of these CMNG surfaces are discussed. The potential of these surfaces to investigate supramolecular self-assembly and on-surface reactions under nanoconfinement conditions is demonstrated.

On Controllability and Applicability of Surface Molecular Self-Assemblies

Molecular self-assembly (MSA) refers to spontaneous arrangement of molecular building blocks into ordered structures governed by weak interactions. Due to its high versatility and reversibility, MSA has been widely employed as a robust bottom-up approach to fabricating low-dimensional functional nanostructures, which are used in various applications in nanoscience and technology. To date, tremendous effort has been devoted to constructing various MSAs at surfaces, ranging from self-assembled monolayers and two-dimensional (2D) nanoporous networks to complex 2D quasicrystals and Sierpiński triangle fractals. However, precise control of the assembled structures and efficient achievement of their full applicability remain two major challenges in the MSA field. As another widely employed bottom-up approach to fabricating nanostructures, on-surface reaction (OSR) refers to a reaction that occurs on the surface and is two-dimensionally confined. OSR offers the possibility to synthesize compounds that may not be feasibly achieved in solution chemistry. Compared with MSA based on weak intermolecular interactions, OSR-based structures possess high thermal and chemical stabilities due to internal strong covalent bonds. In this Account, we briefly overview recent achievements of MSAs on single crystal metal surfaces with a focus on their controllability and applicability in tweaking the properties of the molecular building blocks involved. Emphasis will be particularly placed upon mediation of OSRs with the MSA strategy. To explore surface MSAs, on the one hand, scanning tunneling microscopy and spectroscopy have been routinely employed as the experimental tools to probe the intermolecular interactions as well as geometric and electronic structures of the assemblies at the atomic and molecular levels. On the other hand, density functional theory and molecular dynamics have been theoretically applied to model and calculate the assembling systems, furthering our understanding of the experimental results. In principle, MSA is primarily balanced by molecule-molecule and molecule-substrate interactions under vacuum conditions. In terms of the assembling methodologies, people have been attempting to achieve rational design, accurate prediction, and controllable construction of assembled molecular nanostructures, namely, tentative design of specific backbones and functional groups of the molecular building blocks, and careful control of the assembling parameters including substrate lattice, temperature, coverage, and external environment as well. An obvious goal for the development of these methodologies lies in the ultimate applications of these MSAs. MSA can retrospectively affect the properties of the assembling molecules. For instance, self-assembled structures not only can serve as secondary templates to host guest molecules but also can stabilize surface metal adatoms. In fact, the electronics, magnetism, and optics of MSAs have been successfully explored. In surface chemistry, the MSA strategy can be further applied to mediate OSRs in at least three aspects: tweaking reaction selectivity, changing reaction pathway, and restricting reaction site. The governing principle lies in that the self-assembled molecules are confined in the assemblies so that the pre-exponential factors and the energy barriers in the Arrhenius equation of the involved reactions could be substantially varied because the subtle reaction mechanisms may change upon assembling. In this sense, the MSA strategy can be efficiently exploited to tune the properties of the assembling molecules and mediate OSRs in surface chemistry.

2-D assembly of supramolecular nanoarchitectures on Mg(0001)

In this work, a Mg(0001) single crystal is used as a novel template to grow 2D supramolecular nano-architectures. By using scanning tunnelling microscopy (STM) and high-resolution X-ray photoemission spectroscopy (HR-XPS), the formation of either a homo-molecular or metal-organic network is reported for carboxylic or amino functionalized molecules, respectively.

Molecular platforms as versatile building blocks for multifunctional photoswitchable surfaces

Structurally well-defined arrangements of multiple functional groups can be prepared by self-assembly of mixed monolayers based on molecular platforms.

Self-Assembled Monolayers as Templates for Linearly Nanopatterned Covalent Chemical Functionalization of Graphite and Graphene Surfaces

An approach for nanoscale covalent functionalization of graphite surfaces employing self-assembled molecular monolayers of n-alkanes as templating masks is presented. Linearly aligned aryl groups with a lateral periodicity of 5 or 7 nm are demonstrated utilizing molecular templates of different lengths. The key feature of this approach is the use of a phase separated solution double layer consisting of a thin organic layer containing template molecules topped by an aqueous layer containing aryldiazonium molecules capable of electrochemical reduction to generate aryl radicals which bring about surface grafting. Upon sweeping of the potential, lateral displacement dynamics at the n-alkane terminal edges acts in conjunction with electrochemical diffusion to result in templated covalent bond formation in a linear fashion. This protocol was demonstrated to be applicable to linear grafting of graphene. The present processing described herein is useful for the realization of rationally designed nanoscale materials.

Supramolecular Assemblies on Surfaces: Nanopatterning, Functionality, and Reactivity

Understanding how molecules interact to form large-scale hierarchical structures on surfaces holds promise for building designer nanoscale constructs with defined chemical and physical properties. Here, we describe early advances in this field and highlight upcoming opportunities and challenges. Both direct intermolecular interactions and those that are mediated by coordinated metal centers or substrates are discussed. These interactions can be additive, but they can also interfere with each other, leading to new assemblies in which electrical potentials vary at distances much larger than those of typical chemical interactions. Earlier spectroscopic and surface measurements have provided partial information on such interfacial effects. In the interim, scanning probe microscopies have assumed defining roles in the field of molecular organization on surfaces, delivering deeper understanding of interactions, structures, and local potentials. Self-assembly is a key strategy to form extended structures on surfaces, advancing nanolithography into the chemical dimension and providing simultaneous control at multiple scales. In parallel, the emergence of graphene and the resulting impetus to explore 2D materials have broadened the field, as surface-confined reactions of molecular building blocks provide access to such materials as 2D polymers and graphene nanoribbons. In this Review, we describe recent advances and point out promising directions that will lead to even greater and more robust capabilities to exploit designer surfaces.

Exploring triazine and heptazine based self assembled molecular materials through first principles investigations

Two-dimensional materials formed from the molecular self assembly of monomers through noncovalent interactions are of great importance in designing complex nanostructures with desired properties. The carbon nitride based heterocyclic systems, triazine and heptazine, are found to be promising candidates for generating various self assembled materials through (N....H) hydrogen bonding. Here, we explored graphyne and graphdiyne-like self assembled structures for carbon nitride materials using the density functional theory calculations. We systematically investigated the monolayer structures, stacked structures in different configurations, as well as the surface assembled structures on the Au(111) surface. In all four different monolayer structures, the monomers interact through the N...H hydrogen bonding. The electronic structure results indicate that the electronic properties in these structures can be tuned through the variation in the length of the acetylinic unit. The minimum energy stacked bilayer structure of triazine based material exactly matches with the experimentally reported structure. Surface assembled studies of the triazine based system show strong interaction between the Au(111) surface and the carbon nitride monolayer. Graphical abstract Self assembled two-dimensional molecular materials as well as the surface assemblies of triazine and heptazine based precursors are computationally investigated.

Potential Driven Non-Reactive Phase Transitions of Ordered Porphyrin Molecules on Iodine-Modified Au(100): An Electrochemical Scanning Tunneling Microscopy (EC-STM) Study

The modelling of long-range ordered nanostructures is still a major issue for the scientific community. In this work, the self-assembly of redox-active tetra(N-methyl-4-pyridyl)-porphyrin cations (H2TMPyP) on an iodine-modified Au(100) electrode surface has been studied by means of Cyclic Voltammetry (CV) and in-situ Electrochemical Scanning Tunneling Microscopy (EC-STM) with submolecular resolution. While the CV measurements enable conclusions about the charge state of the organic species, in particular, the potentio-dynamic in situ STM results provide new insights into the self-assembly phenomena at the solid-liquid interface. In this work, we concentrate on the regime of positive electrode potentials in which the adsorbed molecules are not reduced yet. In this potential regime, the spontaneous adsorption of the H2TMPyP molecules on the anion precovered surface yields the formation of up to five different potential-dependent long-range ordered porphyrin phases. Potentio-dynamic STM measurements, as a function of the applied electrode potential, show that the existing ordered phases are the result of a combination of van der Waals and electrostatic interactions.

Silver nanoparticles incorporated konjac glucomannan-montmorillonite nacre-like composite films for antibacterial applications

Artificial nacre-like konjac glucomannan-Montmorillonite (KGM-MTM) composite films with 'brick and mortar' microstructures have been fabricated based on using KGM-MTM hybrid nanosheets as building blocks. In the designed fabrication procedure, we assembled hybrid building blocks with a thin layer of KGM coating on the MTM nanosheets to form KGM-MTM composite film via vacuum filtration. The nacre-like microstructures enhanced the light transmission performance and mechanical properties (Tensile strength: 116 MPa) of KGM-MTM composite films. Additionally, Ag nanoparticles (Ag NPs) can be incorporated into the layered structures of KGM-MTM composite films via an in situ reduced method. It was found that KGM-MTM-Ag composite films significantly suppress bacterial growth, which makes them potentially applicable as antimicrobial films in the biomedical field.

Characterization of Robust and Free-Standing 2D-Nanomembranes of UV-Polymerized Diacetylene Lipids

Free-standing lipid membranes are promising as artificial functional membrane systems for application in separation, filtration, and nanopore sensing. To improve the mechanical properties of lipid membranes, UV-polymerized lipids have been introduced. We investigated free-standing as well as substrate-supported monolayers of 1-palmitoyl-2-(10,12-tricosadiynoyl)- sn-glycero-3-phosphoethanolamine (PTPE) and 1,2-bis(10,12-tricosadiynoyl)- sn-glycero-3-phosphocholine (DiynePC) and characterized them with respect to their structure, morphology, and stability. Using helium ion microscopy (HIM), we were able to visualize the integrity of the lipid 2D-nanomembranes spanning micrometer-sized voids under high-vacuum conditions. Atomic force microscopy (AFM) investigations under ambient conditions revealed formation of intact and robust pore-spanning 2D-nanomembranes up to 8 × 2 μm² in size. Analysis by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) verified a distinct reduction of signal at 2143 cm^-1 from diacetylene groups in the 2D-nanomembranes after UV-polymerization. Further high-resolution AFM investigations of unpolymerized lipid monolayers revealed a well-ordered two-dimensional network, when deposited on highly oriented pyrolytic graphite (HOPG). These structures were inhibited for polymerized adlayers. Structural models for the molecular arrangement of the adlayers are proposed and discussed.

Steering on-surface reactions with self-assembly strategy

The control of assembly structures that subsequently help achieve viable functionalities has been one of the key motivations for the exploration of surface molecular assembly. In terms of its functionality and applicability, the assembly is explored as a strategy to steer on-surface reactions primarily by two methods: assembly-assisted and assembly-involved reactions. The functions of the self-assembly strategy are threefold: tweaking reaction selectivities, steering reaction pathways, and directing reaction sites. The governing principle herein is that the assembly strategy can apply a surface confinement effect that affects the energy barrier and pre-exponential factor of the Arrhenius equation for the dynamics of the target reaction. Development of such a strategy may reveal new routes to steer on-surface reactions and even single molecule properties in surface chemistry.

Host-guest chemistry in two-dimensional supramolecular networks

Nanoporous supramolecular networks physisorbed on solid surfaces have been extensively used to immobilize a variety of guest molecules. Host-guest chemistry in such two-dimensional (2D) porous networks is a rapidly expanding field due to potential applications in separation technology, catalysis and nanoscale patterning. Diverse structural topologies with high crystallinity have been obtained to capture molecular guests of different sizes and shapes. A range of non-covalent forces such as hydrogen bonds, van der Waals interactions, coordinate bonds have been employed to assemble the host networks. Recent years have witnessed a surge in the activity in this field with the implementation of rational design strategies for realizing controlled and selective guest capture. In this feature article, we review the development in the field of surface-supported host-guest chemistry as studied by scanning tunneling microscopy (STM). Typical host-guest architectures studied on solid surfaces, both under ambient conditions at the solution-solid interface as well as those formed at the ultrahigh vacuum (UHV)-solid interface, are described. We focus on isoreticular host networks, hosts functionalized pores and dynamic host-guest systems that respond to external stimuli.

Growth of regular nanometric molecular arrays on a functional 2D template based on a chemical guest-host approach

A regular 2D array of crown molecules, which would spontaneously self-assemble into disordered molecular clusters, is obtained by exploiting a guest-host process, based on the chemical affinity between amino and carboxylic groups on a gold surface. First a carboxylic organic template is formed, which then serves as a host for amino-functionalized crown molecules. The amino-carboxylic interaction thereby drives the formation of a monolayer of guest molecules, regularly distributed at the nanometer scale, preventing their aggregation in unordered clusters observed on a bare gold surface. This method, which can be applied to other guest molecules, represents a novel route to overcome the shape-matching requirements of the standard guest-host architectures. Furthermore, it is intrinsically selective, due to the chemical nature of the anchoring process.

Mesoscale Graphene-like Honeycomb Mono- and Multilayers Constructed via Self-Assembly of Coclusters

Honeycomb structure endows graphene with extraordinary properties. But could a honeycomb monolayer superlattice also be generated via self-assembly of colloids or nanoparticles? Here we report the construction of mono- and multilayer molecular films with honeycomb structure that can be regarded as self-assembled artificial graphene (SAAG). We construct fan-shaped molecular building blocks by covalently connecting two kinds of clusters, one polyoxometalate and four polyhedral oligomeric silsesquioxanes. The precise shape control enables these complex molecules to self-assemble into a monolayer 2D honeycomb superlattice that mirrors that of graphene but on the mesoscale. The self-assembly of the SAAG was also reproduced via coarse-grained molecular simulations of a fan-shaped building block. It revealed a hierarchical process and the key role of intermediate states in determining the honeycomb structure. Experimental images also show a diversity of bi- and trilayer stacking modes. The successful creation of SAAG and its stacks opens up prospects for the preparation of novel self-assembled nanomaterials with unique properties.