Chemical Wiring and Soldering toward All-Molecule Electronic Circuitry

Identifying Carbon-Carbon Triple Bonds from Double Bonds via Single-Molecule Conductance

Molecular-scale electronics focuses on understanding and utilizing charge transport through individual molecules. A key issue is the charge transport capability of a single molecule characterized by current decay. We visualize the on-site formation of conjugated polymers with varying carbon-carbon bond orders by using scanning tunneling microscopy and noncontact atomic force microscopy. Although carbon-carbon double bonds and triple bonds exhibit similar electronic characteristics, single-molecule conductance measurements reveal distinct features based on different levels of conjugation. These findings, supported by density functional theory calculations, indicate that a higher bond order results in greater electron density and more symmetric molecular orbitals, leading to larger transmission rates and more rigid frontier orbitals. Consequently, this contributes to a higher conductance and a lower decay constant. These findings enhance the understanding of bond orders in molecular electronics and should facilitate the development of single-molecule devices and the applications of nanoscale circuitry.

Lateral nanoarchitectonics from nano to life: ongoing challenges in interfacial chemical science

Lateral nanoarchitectonics is a method of precisely designing functional materials from atoms, molecules, and nanomaterials (so-called nanounits) in two-dimensional (2D) space using knowledge of nanotechnology. Similar strategies can be seen in biological systems; in particular, biological membranes ingeniously arrange and organise functional units within a single layer of units to create powerful systems for photosynthesis or signal transduction and others. When our major lateral nanoarchitectural approaches such as layer-by-layer (LbL) assembly and Langmuir-Blodgett (LB) films are compared with biological membranes, one finds that lateral nanoarchitectonics has potential to become a powerful tool for designing advanced functional nanoscale systems; however, it is still rather not well-developed with a great deal of unexplored possibilities. Based on such a discussion, this review article examines the current status of lateral nanoarchitectonics from the perspective of in-plane functional structure organisation at different scales. These include the extension of functions at the molecular level by on-surface synthesis, monolayers at the air-water interface, 2D molecular patterning, supramolecular polymers, macroscopic manipulation and functionality of molecular machines, among others. In many systems, we have found that while the targets are very attractive, the research is still in its infancy, and many challenges remain. Therefore, it is important to look at the big picture from different perspectives in such a comprehensive review. This review article will provide such an opportunity and help us set a direction for lateral nanotechnology toward more advanced functional organization.

Interface-Interactive Nanoarchitectonics: Solid and/or Liquid

The methodology of nanoarchitectonics is to construct functional materials using nanounits such as atoms, molecules, and nanoobjects, just like architecting buildings. Nanoarchitectonics pursues the ultimate concept of materials science through the integration of related fields. In this review paper, under the title of interface-interactive nanoarchitectonics, several examples of structure fabrication and function development at interfaces will be discussed, highlighting the importance of architecting materials with nanoscale considerations. Two sections provide some examples at the solid and liquid surfaces. In solid interfacial environments, molecular structures can be precisely observed and analyzed with theoretical calculations. Solid surfaces are a prime site for nanoarchitectonics at the molecular level. Nanoarchitectonics of solid surfaces has the potential to pave the way for cutting-edge functionality and science based on advanced observation and analysis. Liquid surfaces are more kinetic and dynamic than solid interfaces, and their high fluidity offers many possibilities for structure fabrications by nanoarchitectonics. The latter feature has advantages in terms of freedom of interaction and diversity of components, therefore, liquid surfaces may be more suitable environments for the development of functionalities. The final section then discusses what is needed for the future of material creation in nanoarchitectonics.

Nanoscale Surface Chemical Patterning of Soft Polyacrylamide with Elastic Modulus Similar to Soft Tissue

Nanometer-scale control over surface functionalization of soft gels is important for a variety of applications including controlling interactions with cells for in vitro cell culture and for regenerative medicine. Recently, we have shown that it is possible to transfer a nanometer-thick precision functional polymer layer to the surface of relatively stiff polyacrylamide gels. Here, we develop a fundamental understanding of the way in which the precision polymer backbone participates in the polyacrylamide radical polymerization and cross-linking process, which enables us to generate high-efficiency transfer to much softer hydrogels (down to 5 kPa) with stiffness similar to that of soft tissue. This approach creates hydrogel surfaces with exposed nanostructured functional arrays that open the door to controlled ligand presentation on soft hydrogel surfaces.

Molecular-level periodic arrays of long-chain poly(3-hexylthiophene-2,5-diyl) driven by an electric field

Two-dimensional (2D) periodic arrays of conductive polymers represent attractive platforms for wiring functional molecules into the integrated circuits of molecular electronics. However, the large-scale assembly of polymer periodic arrays at the molecular level faces challenges such as curling, twisting, and aggregation. Here, we assembled the periodic arrays of long-chain poly(3-hexylthiophene-2,5-diyl) (P3HT, Mw = 65 k) at the solid-liquid interface by applying an electric field, within which the charged chain segments were aligned. Atomic force microscopy (AFM) imaging revealed that individual P3HT chains assemble into monolayers featuring face-on orientation, extended chain conformation and isolated packing, which is thermodynamically more stable than folded chains in 2D polycrystals. The assembly process is initiated with the formation of disordered clusters and progresses through voltage-dependent nucleation and growth of extended-chain arrays, wherein continuous conformational adjustments along the nucleation pathway exhibit dependence on the cluster size.

Toward Practical Single-Molecule/Atom Switches

Electronic switches have been considered to be one of the most important components of contemporary electronic circuits for processing and storing digital information. Fabricating functional devices with building blocks of atomic/molecular switches can greatly promote the minimization of the devices and meet the requirement of high integration. This review highlights key developments in the fabrication and application of molecular switching devices. This overview offers valuable insights into the switching mechanisms under various stimuli, emphasizing structural and energy state changes in the core molecules. Beyond the molecular switches, typical individual metal atomic switches are further introduced. A critical discussion of the main challenges for realizing and developing practical molecular/atomic switches is provided. These analyses and summaries will contribute to a comprehensive understanding of the switch mechanisms, providing guidance for the rational design of functional nanoswitch devices toward practical applications.

Quantifying the conductivity of a single polyene chain by lifting with an STM tip

Conjugated polymers are promising candidates for molecular wires in nanoelectronics, with flexibility in mechanics, stability in chemistry and variety in electrical conductivity. Polyene, as a segment of polyacetylene, is a typical conjugated polymer with straightforward structure and wide-range adjustable conductance. To obtain atomic scale understanding of charge transfer in polyene, we have measured the conductance of a single polyene-based molecular chain via lifting it up with scanning tunneling microscopy tip. Different from semiconducting characters in pristine polyene (polyacetylene), high conductance and low decay constant are obtained, along with an electronic state around Fermi level and characteristic vibrational mode. These observed phenomena result from pinned molecular orbital owing to molecule-electrode coupling at the interface, and weakened bond length alternation due to electron-phonon coupling inside single molecular chain. Our findings emphasize the interfacial characteristics in molecular junctions and promising properties of polyene, with single molecular conductance as a vital tool for bringing insights into the design and construction of nanodevices.

STM studies on porphyrins and phthalocyanines at the liquid/solid interface for molecular-scale electronics

Porphyrins and phthalocyanines are promising candidates for single-molecule electronics. Among the many characterization tools, scanning tunneling microscopy (STM) represents a very powerful one to gain insight into the electronic properties at the molecular level, by correlating the charge transport behaviours of π-conjugated molecules with ultrahigh resolution imaging. In view of the sophistication of molecular self-assembly in the presence of a solution phase, in this frontier, we focus on STM studies on porphyrins and phthalocyanines at the liquid/solid interface, placing emphasis on the electronic and magnetic properties, as well as the switching behaviour of surface-confined or surface-anchored molecules. Furthermore, we have also addressed the topics of potential that can be exploited in this area.

Insights into the Polymerization Reactions on Solid Surfaces Provided by Scanning Tunneling Microscopy

Understanding the polymerization process at the molecular level is essential for the rational design and synthesis of polymers with controllable structures and properties. Scanning tunneling microscopy (STM) is one of the most important techniques to investigate the structures and reactions on conductive solid surfaces, and it has successfully been used to reveal the polymerization process on the surface at the molecular level in recent years. In this Perspective, after a brief introduction of on-surface polymerization reactions and STM, we focus on the applications of STM in the study of the processes and mechanism of on-surface polymerization, from one-dimensional to two-dimensional polymerization reactions. We conclude by a discussion of the challenges and perspectives on this topic.

Designing Interfacial Reactions for Nanometer-Scale Surface Patterning of PDMS with Controlled Elastic Modulus

Control over the surface chemistry of elastomers such as polydimethylsiloxane (PDMS) is important for many applications. However, achieving nanostructured chemical control on amorphous material interfaces below the length scale of substrate heterogeneity is not straightforward, and can be particularly difficult to decouple from changes in network structure that are required for certain applications (e.g., variation of elastic modulus for cell culture). We have recently reported a new method for precisely structured surface functionalization of PDMS and other soft materials, which displays high densities of ligands directly on the material surface, maximizing steric accessibility. Here, we systematically examine structural factors in the PDMS components (e.g., base and cross-linker structures) that impact efficiency of the interfacial reaction that leads to surface functionalization. Applying this understanding, we demonstrate routes for generating equivalent nanometer-scale functional patterns on PDMS with elastic moduli from 0.013 to 1.4 MPa, establishing a foundation for use in applications such as cell culture.

Plenty of Room at the Top: A Multi-Scale Understanding of nm-Resolution Polymer Patterning on 2D Materials

Lamellar phases of alkyldiacetylenes in which the alkyl chains lie parallel to the substrate represent a straightforward means for scalable 1-nm-resolution interfacial patterning. This capability has the potential for substantial impacts in nanoscale electronics, energy conversion, and biomaterials design. Polymerization is required to set the 1-nm functional patterns embedded in the monolayer, making it important to understand structure-function relationships for these on-surface reactions. Polymerization can be observed for certain monomers at the single-polymer scale using scanning probe microscopy. However, substantial restrictions on the systems that can be effectively characterized have limited utility. Here, using a new multi-scale approach, we identify a large, previously unreported difference in polymerization efficiency between the two most widely used commercial diynoic acids. We further identify a core design principle for maximizing polymerization efficiency in these on-surface reactions, generating a new monomer that also exhibits enhanced polymerization efficiency.

Lipids: An Atomic Toolkit for the Endless Frontier

The evolution of lipids in nanoscience exemplifies the powerful coupling of advances in science and technology. Here, we describe two waves of discovery and innovation in lipid materials: one historical and one still building. The first wave leveraged the relatively simple capability for lipids to orient at interfaces, building layers of functional groups. This simple form of building with atoms yielded a stunning range of technologies: lubricant additives that dramatically extended machine lifetimes, molecules that enabled selective ore extraction in mining, and soaps that improved human health. It also set the stage for many areas of modern nanoscience. The second wave of lipid materials, still growing, uses the more complex toolkits lipids offer for building with atoms, including controlling atomic environment to control function (e.g., pK_a tuning) and the generation of more arbitrary two-dimensional and three-dimensional structures, including lipid nanoparticles for COVID-19 mRNA vaccines.

Self-Assembly Behavior of Diacetylenic Acid Molecules upon Vapor Deposition: Odd-Even Effect on the Film Morphology

A series of linear carboxylic acids containing diacetylenic units at different positions along the chain (C₁₂ H₂₅ (C≡C)₂ (CH₂ )_n COOH, n=7-11) were vacuum-deposited on clean silica substrates. The morphologies of the initial films after UV irradiation were studied. A clear odd-even effect on the morphology of the initial film was observed in that, depending on the spacer length between the diacetylenic unit and carboxyl head group, rings or dendrites of acid dimer layers were obtained. A molecular dynamic simulation of the aggregation process suggests that two competing intermolecular interactions and thus aggregation directions are involved and modulated by the odd or even carbon chain length. Further modulation of the interaction by substitution of a phenyl group at the terminus of the chain or by changing the carboxyl head group to an amidobenzoic acid head group led to a similar odd-even effect but with different dimensions or trends, which can be rationalized similarly. These results give the opportunity to create aligned conjugated polymer chains of different dimensions through self-assembly for applications in molecular/organic electronics.

Large-Scale Noncovalent Functionalization of 2D Materials through Thermally Controlled Rotary Langmuir-Schaefer Conversion

As two-dimensional (2D) materials are more broadly utilized as components of hybrid materials, controlling their surface chemistry over large areas through noncovalent functionalization becomes increasingly important. Here, we demonstrate a thermally controlled rotary transfer stage that allows areas of a 2D material to be continuously cycled into contact with a Langmuir film. This approach enables functionalization of large areas of the 2D material and simultaneously improves long-range ordering, achieving ordered domain areas up to nearly 10 000 μm². To highlight the layer-by-layer processing capability of the rotary transfer stage, large-area noncovalently adsorbed monolayer films from an initial rotary cycle were used as templates to assemble ultranarrow gold nanowires from solution. The process we demonstrate would be readily extensible to roll-to-roll processing, addressing a longstanding challenge in scaling Langmuir-Schaefer transfer for practical applications.

Structural and Photophysical Templating of Conjugated Polyelectrolytes with Single-Stranded DNA

A promising approach to influence and control the photophysical properties of conjugated polymers is directing their molecular conformation by templating. We explore here the templating effect of single-stranded DNA oligomers (ssDNAs) on cationic polythiophenes with the goal to uncover the intermolecular interactions that direct the polymer backbone conformation. We have comprehensively characterized the optical behavior and structure of the polythiophenes in conformationally distinct complexes depending on the sequence of nucleic bases and addressed the effect on the ultrafast excited-state relaxation. This, in combination with molecular dynamics simulations, allowed us a detailed atomistic-level understanding of the structure-property correlations. We find that electrostatic and other noncovalent interactions direct the assembly with the polymer, and we identify that optimal templating is achieved with (ideally 10-20) consecutive cytosine bases through numerous π-stacking interactions with the thiophene rings and side groups of the polymer, leading to a rigid assembly with ssDNA, with highly ordered chains and unique optical signatures. Our insights are an important step forward in an effective approach to structural templating and optoelectronic control of conjugated polymers and organic materials in general.

Controlling a Chemical Coupling Reaction on a Surface: Tools and Strategies for On-Surface Synthesis

On-surface synthesis is appearing as an extremely promising research field aimed at creating new organic materials. A large number of chemical reactions have been successfully demonstrated to take place directly on surfaces through unusual reaction mechanisms. In some cases the reaction conditions can be properly tuned to steer the formation of the reaction products. It is thus possible to control the initiation step of the reaction and its degree of advancement (the kinetics, the reaction yield); the nature of the reaction products (selectivity control, particularly in the case of competing processes); as well as the structure, position, and orientation of the covalent compounds, or the quality of the as-formed networks in terms of order and extension. The aim of our review is thus to provide an extensive description of all tools and strategies reported to date and to put them into perspective. We specifically define the different approaches available and group them into a few general categories. In the last part, we demonstrate the effective maturation of the on-surface synthesis field by reporting systems that are getting closer to application-relevant levels thanks to the use of advanced control strategies.

Symmetry breakdown of 4,4″-diamino-p-terphenyl on a Cu(111) surface by lattice mismatch

Site-selective functionalization of only one of two identical chemical groups within one molecule is highly challenging, which hinders the production of complex organic macromolecules. Here we demonstrate that adsorption of 4,4″-diamino-p-terphenyl on a metal surface leads to a dissymmetric binding affinity. With low temperature atomic force microscopy, using CO-tip functionalization, we reveal the asymmetric adsorption geometries of 4,4″-diamino-p-terphenyl on Cu(111), while on Au(111) the symmetry is retained. This symmetry breaking on Cu(111) is caused by a lattice mismatch and interactions with the subsurface atomic layer. The dissymmetry results in a change of the binding affinity of one of the amine groups, leading to a non-stationary behavior under the influence of the scanning tip. Finally, we exploit this dissymmetric binding affinity for on-surface self-assembly with 4,4″-diamino-p-terphenyl for side-preferential attachment of 2-triphenylenecarbaldehyde. Our findings provide a new route towards surface-induced dissymmetric activation of a symmetric compound.

In a symmetric molecule with identical functional groups, selective activation of only one site is challenging. Here, the authors show that 4,4″-diamino-p-terphenyl adsorbs asymmetrically to a metal surface, leading to a change in binding affinity of one of its amine groups.

Diacetylene polymerization on a bulk insulator surface

Molecular electronics has great potential to surpass known limitations in conventional silicon-based technologies. The development of molecular electronics devices requires reliable strategies for connecting functional molecules by wire-like structures. To this end, diacetylene polymerization has been discussed as a very promising approach for contacting single molecules with a conductive polymer chain. A major challenge for future device fabrication is transferring this method to bulk insulator surfaces, which are mandatory to decouple the electronic structure of the functional molecules from the support surface. Here, we provide experimental evidence for diacetylene polymerization of 3,3'-(1,3-butadiyne-1,4-diyl)bisbenzoic acid precursors on the (10.4) surface of calcite, a bulk insulator with a band gap of around 6 eV. When deposited on the surface held at room temperature, ordered islands with a (1 × 3) superstructure are observed using dynamic atomic force microscopy. A distinct change is revealed upon heating the substrate to 485 K. After heating, molecular stripes with a characteristic inner structure are formed that excellently match the expected diacetylene polymer chains in appearance and repeat distance. The corresponding density functional theory computations reveal molecular-level bonding patterns of both the (1 × 3) superstructure and the formed striped structure, confirming the assignment of on-surface diacetylene polymerization. Transferring the concept of using diacetylene polymerization for creating conductive connections to bulk insulator surfaces paves the way towards application-relevant systems for future molecular electronic devices.

Hierarchically Patterned Noncovalent Functionalization of 2D Materials by Controlled Langmuir-Schaefer Conversion

Noncovalent monolayer chemistries are often used to functionalize 2D materials. Nanoscopic ligand ordering has been widely demonstrated (e.g., lying-down lamellar phases of functional alkanes); however, combining this control with micro- and macroscopic patterning for practical applications remains a significant challenge. A few reports have demonstrated that standing phase Langmuir films on water can be converted into nanoscopic lying-down molecular domains on 2D substrates (e.g., graphite), using horizontal dipping (Langmuir-Schaefer, LS, transfer). Molecular patterns are known to form at scales up to millimeters in Langmuir films, suggesting the possibility of transforming such structures into functional patterns on 2D materials. However, to our knowledge, this approach has not been investigated, and the rules governing LS conversion are not well understood. In part, this is because the conversion process is mechanistically very different from classic LS transfer of standing phases; challenges also arise due to the need to characterize structure in noncovalently adsorbed ligand layers <0.5 nm thick, at scales ranging from millimeters to nanometers. Here, we show that scanning electron microscopy enables diynoic acid lying-down phases to be imaged across this range of scales; using this structural information, we establish conditions for LS conversion to create hierarchical microscopic and nanoscopic functional patterns. Such control opens the door to tailoring noncovalent surface chemistry of 2D materials to pattern local interactions with the environment.

Multimicrometer Noncovalent Monolayer Domains on Layered Materials through Thermally Controlled Langmuir-Schaefer Conversion for Noncovalent 2D Functionalization

As functionalized 2D materials are incorporated into hybrid materials, ensuring large-area structural control in noncovalently adsorbed films becomes increasingly important. Noncovalent functionalization avoids disrupting electronic structure in 2D materials; however, relatively weak molecular interactions in such monolayers typically reduce stability toward solution processing and other common material handling conditions. Here, we find that controlling substrate temperature during Langmuir-Schaefer conversion of a standing phase monolayer of diynoic amphiphiles on water to a horizontally oriented monolayer on a 2D substrate routinely produces multimicrometer domains, at least an order of magnitude larger than those typically achieved through drop-casting. Following polymerization, these highly ordered monolayers retain their structures during vigorous washing with solvents including water, ethanol, tetrahydrofuran, and toluene. These findings point to a convenient and broadly applicable strategy for noncovalent functionalization of 2D materials in applications that require large-area structural control, for instance, to minimize desorption at defects during subsequent solution processing.

Sitting Phase Monolayers of Polymerizable Phospholipids Create Dimensional, Molecular-Scale Wetting Control for Scalable Solution-Based Patterning of Layered Materials

The use of dimensionally ordered ligands on layered materials to direct local electronic structure and interactions with the environment promises to streamline integration into nanostructured electronic, optoelectronic, sensing, and nanofluidic interfaces. Substantial progress has been made in using ligands to control substrate electronic structure. Conversely, using the exposed face of the ligand layer to structure wetting and binding interactions, particularly with scalable solution- or spray-processed materials, remains a significant challenge. However, nature routinely utilizes wetting control at scales from nanometer to micrometer to build interfaces of striking geometric precision and functional complexity, suggesting the possibility of leveraging similar control in synthetic materials. Here, we assemble striped "sitting" phases of polymerizable phospholipids on highly oriented pyrolytic graphite, producing a surface consisting of 1 nm wide hydrophilic stripes alternating with 5 nm wide hydrophobic stripes. Protruding, strongly wetting headgroup chemistries in these monolayers enable formation of rodlike wetted patterns with widths as little as ∼6 nm and lengths up to 100 nm from high-surface-tension liquids (aqueous solutions of glycerol) commonly utilized to assess interfacial wetting properties at larger length scales. In contrast, commonly used lying-down phases of diynoic acids with in-plane headgroups do not promote droplet sticking or directional spreading. These results point to a broadly applicable strategy for achieving high-resolution solution-based patterning on layered materials, utilizing nanometer-wide patterns of protruding, charged functional groups in a noncovalent monolayer to define pattern edges.

Reversible on-surface wiring of resistive circuits

Whilst most studies in single-molecule electronics involve components first synthesized ex situ, there is also great potential in exploiting chemical transformations to prepare devices in situ. Here, as a first step towards this goal, we conduct reversible reactions on monolayers to make and break covalent bonds between alkanes of different lengths, then measure the conductance of these molecules connected between electrodes using the scanning tunneling microscopy-based break junction (STM-BJ) method. In doing so, we develop the critical methodology required for assembling and disassembling surface-bound single-molecule circuits. We identify effective reaction conditions for surface-bound reagents, and importantly demonstrate that the electronic characteristics of wires created in situ agree with those created ex situ. Finally, we show that the STM-BJ technique is unique in its ability to definitively probe surface reaction yields both on a local (∼50 nm2) and pseudo-global (≥10 mm2) level. This investigation thus highlights a route to the construction and integration of more complex, and ultimately functional, surface-based single-molecule circuitry, as well as advancing a methodology that facilitates studies beyond the reach of traditional ex situ synthetic approaches.

Frontiers of supramolecular chemistry at solid surfaces

Supramolecular chemistry on solid surfaces represents an exciting field of research that continues to develop in new and unexpected directions.

Chemistry at the square nanometer: reactivity at liquid/solid interfaces revealed with an STM

An overview is given of single molecule reactivity at a liquid/solid interface employing a scanning tunneling microscope.

Self-assembled diacetylene molecular wire polymerization on an insulating hexagonal boron nitride (0001) surface

The electrical characterization of single-polymer chains on a surface is an important step towards novel molecular device development. The main challenge is the lack of appropriate atomically flat insulating substrates for fabricating single-polymer chains. Here, using atomic force microscopy, we demonstrate that the (0001) surface of an insulating hexagonal boron nitride (h-BN) substrate leads to a flat-lying self-assembled monolayer of diacetylene compounds. The subsequent heating or ultraviolet irradiation can initiate an on-surface polymerization process leading to the formation of long polydiacetylene chains. The frequency of photo-polymerization occurrence on h-BN(0001) is two orders of magnitude higher than that on graphite(0001). This is explained by the enhanced lifetime of the molecular excited state, because relaxation via the h-BN is suppressed due to a large band gap. We also demonstrate that on-surface polymerization on h-BN(0001) is possible even after the lithography process, which opens up the possibility of further electrical investigations.

Iron phthalocyanine on Cu(111): Coverage-dependent assembly and symmetry breaking, temperature-induced homocoupling, and modification of the adsorbate-surface interaction by annealing

We have examined the geometric and electronic structures of iron phthalocyanine assemblies on a Cu(111) surface at different sub- to mono-layer coverages and the changes induced by thermal annealing at temperatures between 250 and 320 °C by scanning tunneling microscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. The symmetry breaking observed in scanning tunneling microscopy images is found to be coverage dependent and to persist upon annealing. Further, we find that annealing to temperatures between 300 and 320 °C leads to both desorption of iron phthalocyanine molecules from the surface and their agglomeration. We see clear evidence of temperature-induced homocoupling reactions of the iron phthalocyanine molecules following dehydrogenation of their isoindole rings, similar to what has been observed for related tetrapyrroles on transition metal surfaces. Finally, spectroscopy indicates a modified substrate-adsorbate interaction upon annealing with a shortened bond distance. This finding could potentially explain a changed reactivity of Cu-supported iron phthalocyanine in comparison to that of the pristine compound.

Self-Assembled Dehydro[24]annulene Monolayers at the Liquid/Solid Interface: Toward On-Surface Synthesis of Tubular π-Conjugated Nanowires

We have studied the self-assembly behavior of dehydro[24]annulene (D24A) derivatives 1, 2a-2d, and 3a-3c at the liquid/solid interface using scanning tunneling microscopy (STM). Both the relative placement and the nature of the four D24A substituents strongly influence the self-assembly pattern. Overall, the eight D24A derivatives examined in this study display seven types of 2D packing patterns. The D24A derivatives 1, 2a, and 3a have either two or four stearate groups and adopt face-on configurations of their macrocyclic cores with respect to the highly oriented pyrolytic graphite (HOPG) surface. Their 2D packing pattern is determined by the interchain spacings and number of stearate substituents. The D24A derivatives 2b-2d and 3b-3c bear hydrogen-bonding carbamate groups to further strengthen intermolecular interactions. Face-on patterns were also observed for most of these compounds, while an unstable edge-on self-assembly was observed in the case of 2b at room temperature. Stable edge-on self-assemblies of D24A derivatives were sought for this work as an important stepping stone to achieving the on-surface topochemical polymerization of these carbon-rich macrocycles into tubular π-conjugated nanowires. The overall factors determining the 2D packing patterns of D24As at the liquid/solid interface are discussed on the basis of theoretical simulations, providing useful guidelines for controlling the self-assembly pattern of future D24A macrocycles.

Nanoarchitectonics for Dynamic Functional Materials from Atomic-/Molecular-Level Manipulation to Macroscopic Action

Objects in all dimensions are subject to translational dynamism and dynamic mutual interactions, and the ability to exert control over these events is one of the keys to the synthesis of functional materials. For the development of materials with truly dynamic functionalities, a paradigm shift from "nanotechnology" to "nanoarchitectonics" is proposed, with the aim of design and preparation of functional materials through dynamic harmonization of atomic-/molecular-level manipulation and control, chemical nanofabrication, self-organization, and field-controlled organization. Here, various examples of dynamic functional materials are presented from the atom/molecular-level to macroscopic dimensions. These systems, including atomic switches, molecular machines, molecular shuttles, motional crystals, metal-organic frameworks, layered assemblies, gels, supramolecular assemblies of biomaterials, DNA origami, hollow silica capsules, and mesoporous materials, are described according to their various dynamic functions, which include short-term plasticity, long-term potentiation, molecular manipulation, switchable catalysis, self-healing properties, supramolecular chirality, morphological control, drug storage and release, light-harvesting, mechanochemical transduction, molecular tuning molecular recognition, hand-operated nanotechnology.

Nanojunction between fullerene and one-dimensional conductive polymer on solid surfaces

Bottom-up creation of huge molecular complexes by covalently interconnecting functional molecules and conductive polymers is a key technology for constructing nanoscale electronic circuits. In this study, we have created an array of molecule-polymer nanojunctions from C60 molecules and polydiacetylene (PDA) nanowires at designated positions on solid surfaces by controlling self-assemblies and intermolecular chemical reactions of molecular ingredients predeposited onto the surfaces. In the proposed method, the construction of each nanojunction spontaneously proceeds via two types of chemical reactions: a chain polymerization among self-assembled diacetylene compound molecules for creating a single PDA nanowire and a subsequent cycloaddition reaction between the propagating forefront part of the PDA backbone and a single C60 molecule adsorbed on the surface. Scanning tunneling microscopy has proved that the C60 molecule is covalently connected to each end of the π-conjugated PDA backbone. Furthermore, the decrease in the energy gap of the C60 molecule in nanojunctions is observed as compared with that of pristine C60 molecules, which is considered to be due to the covalent interaction between the PDA edge and the C60 molecule.

Local electronic and chemical structure of oligo-acetylene derivatives formed through radical cyclizations at a surface

Semiconducting π-conjugated polymers have attracted significant interest for applications in light-emitting diodes, field-effect transistors, photovoltaics, and nonlinear optoelectronic devices. Central to the success of these functional organic materials is the facile tunability of their electrical, optical, and magnetic properties along with easy processability and the outstanding mechanical properties associated with polymeric structures. In this work we characterize the chemical and electronic structure of individual chains of oligo-(E)-1,1'-bi(indenylidene), a polyacetylene derivative that we have obtained through cooperative C1-C5 thermal enediyne cyclizations on Au(111) surfaces followed by a step-growth polymerization of the (E)-1,1'-bi(indenylidene) diradical intermediates. We have determined the combined structural and electronic properties of this class of oligomers by characterizing the atomically precise chemical structure of individual monomer building blocks and oligomer chains (via noncontact atomic force microscopy (nc-AFM)), as well as by imaging their localized and extended molecular orbitals (via scanning tunneling microscopy and spectroscopy (STM/STS)). Our combined structural and electronic measurements reveal that the energy associated with extended π-conjugated states in these oligomers is significantly lower than the energy of the corresponding localized monomer orbitals, consistent with theoretical predictions.

Temperature-induced transitions of self-assembled phthalocyanine molecular nanoarrays at the solid-liquid interface: from randomness to order

A promising approach to create functional nanoarrays is supramolecular self-assembly at liquid-solid interfaces. In the present investigation, we report on the self-assembly of phthalocyanine arrays using triphenylene-2,6,10-tricarboxylic acid (H₃TTCA) as a molecular nanotemplate. Five different metastable arrays are achieved in the study, including a thermodynamically stable configuration. Scanning tunneling microscopy (STM) measurements and density function theory (DFT) calculations are utilized to reveal the formation mechanism of the molecular nanoarrays. In general, the transformation process of nanoarrays is regulated by the synergies of a template effect and thermodynamic balance.