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Chemistry on solid surfaces is central to many re-search areas of practical interest, such as synthesis, catalysis, electrochemistry, photochemistry, and materials science. A comprehensive understanding of the nanoscale on-surface chemistry involved in these areas is important for establishing composi-tion-structure-performance relationships. With the rapid development of tip-enhanced Raman spectros-copy (TERS), it has become possible to investigate physical and chemical processes on suitable surfaces at the nanoscale level and in real space. In this review, after a brief introduction of the background of on-surface chemistry and TERS, we systematically dis-cuss the progress in the application of TERS in this field. Our focus is the applications of TERS to nano-scale coordination processes, decomposition reac-tions, polymerization processes, electrochemical reactions, catalytic chemistry, and functionalization chemistry on solid surfaces. We conclude by discuss-ing the future challenges and development of TERS techniques and related applications in on-surface chemistry. ISSN:2096-5745

Two-dimensional (2D) molecular materials have attracted immense attention due to their unique properties, promising a wide range of exciting applications. To understand the structure-property relationship of these low-dimensional materials, sensitive analytical tools capable of providing structural and chemical characterisation at the nanoscale are required. However, most conventional analytical techniques fail to meet this challenge, especially in a label-free and non-destructive manner under ambient conditions. In the last two decades, tip-enhanced Raman spectroscopy (TERS) has emerged as a powerful analytical technique for nanoscale chemical characterisation by combining the high spatial resolution of scanning probe microscopy and the chemical sensitivity and specificity of surface-enhanced Raman spectroscopy. In this review article, we provide an overview of the application of TERS for nanoscale chemical analysis of 2D molecular materials, including 2D polymers, biomimetic lipid membranes, biological cell membranes, and 2D reactive systems. The progress in the structural and chemical characterisation of these 2D materials is demonstrated with key examples from our as well as other laboratories. We highlight the unique information that TERS can provide as well as point out the common pitfalls in experimental work and data interpretation and the possible ways of averting them., Nanoscale, 15 (3), ISSN:2040-3364, ISSN:2040-3372

We report a molecular investigation of a cobalt phthalocyanine (CoPc)-catalyzed CO2 reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO2 -purged electrolyte environment. The ECSTM experiments indicate the proportion of high-contrast species correlated with the reduction of CoII Pc (-0.2 V vs. saturated calomel electrode (SCE)). The high-contrast species is ascribed to the CoPc-CO2 complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc-CO2 to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO2 , and the latter is the rate-limiting step. The rate constant of the formation and dissociation of CoPc-CO2 is estimated on the basis of the in situ ECSTM experiment.

The quality of crystalline two-dimensional (2D) polymers1-6 is intimately related to the elusive polymerization and crystallization processes. Understanding the mechanism of such processes at the (sub)molecular level is crucial to improve predictive synthesis and to tailor material properties for applications in catalysis7-10 and (opto)electronics11,12, among others13-18. We characterize a model boroxine 2D dynamic covalent polymer, by using in situ scanning tunnelling microscopy, to unveil both qualitative and quantitative details of the nucleation-elongation processes in real time and under ambient conditions. Sequential data analysis enables observation of the amorphous-to-crystalline transition, the time-dependent evolution of nuclei, the existence of 'non-classical' crystallization pathways and, importantly, the experimental determination of essential crystallization parameters with excellent accuracy, including critical nucleus size, nucleation rate and growth rate. The experimental data have been further rationalized by atomistic computer models, which, taken together, provide a detailed picture of the dynamic on-surface polymerization process. Furthermore, we show how 2D crystal growth can be affected by abnormal grain growth. This finding provides support for the use of abnormal grain growth (a typical phenomenon in metallic and ceramic systems) to convert a polycrystalline structure into a single crystal in organic and 2D material systems. ispartof: NATURE vol:603 issue:7903 pages:835-+ ispartof: location:England status: published

Herein we report the impact of covalent modification (grafting), inducing lateral nanoconfinement conditions, on the self-assembly of a quinonoid zwitterion derivative into self-assembled molecular networks at the liquid/solid interface. At low concentrations where the compound does not show self-assembly behaviour on bare highly oriented pyrolytic graphite (HOPG), close-packed self-assembled structures are visualized by scanning tunneling microscopy on covalently modified HOPG. The size of the self-assembled domains decreases with increasing the density of grafted molecules, i.e. the molecules covalently bound to the surface. The dynamics of domains are captured with molecular resolution, revealing not only time-dependent growth and shrinkage processes but also the orientation conversion of assembled domains. Grafted pins play a key role in initiating the formation of on-surface molecular self-assembly and their stabilization, providing an elegant route to study various aspects of nucleation and growth processes of self-assembled molecular networks., Chemical Science, 13 (44), ISSN:2041-6520, ISSN:2041-6539

Metal-organic coordination structures at interfaces play an essential role in many biological and chemical systems. Understanding the molecular specificity, orientation, and spatial distribution of the coordination complexes at the nanometer scale is of great importance for effective molecular engineering of nanostructures and fabrication of functional devices with controllable properties. However, fundamental properties of such coordination systems are still rarely studied directly. In this work, we present a spectroscopic approach on the basis of tip-enhanced Raman spectroscopy (TERS) to investigate cobalt(II) tetraphenyl-porphyrine coordination species on the scale of a single molecule under ambient conditions. Coordination species anchored on gold surfaces modified with pyridine thiol self-assembled monolayers can be spectroscopically distinguished and mapped with ca. 2 nm resolution. In addition, in combination with density functional theory simulations, the adsorption configuration and molecular orientation of the coordination complexes are also revealed using TERS imaging. ISSN:0002-7863 ISSN:1520-5126

We report an electrochemical scanning tunneling microscopy (ECSTM) study of the 5,10,15,20-tetraphenyl-21 H,23 H-porphyrin cobalt(II) (CoTPP) catalyzed oxygen evolution reaction (OER). A highly ordered self-assembled monolayer of CoTPP is formed on the Au(111) electrode. Cyclic voltammetry results show the OER activity of the electrode is enhanced with the increasing alkalinity of the electrolytes. The CoTPP molecules appear as two symmetric bright spots in STM images in alkaline solution, which is in sharp contrast to that in acidic solution. The molecular contour changes are attributed to the formation of the CoTPP-OH- species before OER, which is further confirmed by UV-vis absorption spectroscopy. In situ ECSTM results reveal the evolution from the CoTPP-OH- species to CoTPP molecules during OER.

Metallofullerenes have a cage-shaped molecular structure and special properties derived from encapsulated metal atoms. Owing to the ball-like fullerene cage, it is still a challenge to manipulate the metallofullerene molecule and to control its properties. Herein, we use the molecular carbon nanoring of [12]cycloparaphenylene to hoop the C80-based metallofullerene Y3N@C80 and azafullerene Y2@C79N, resulting in a stable supramolecular complex, induced molecule orientation, changed assembly behavior, and tunable spin state. These supramolecular complexes and their host–guest interactions were systematically characterized by DFT-calculations, spectroscopy, NMR, and electrochemical analysis. Scanning tunneling microscopy was employed to reveal that the metallofullerene guests dominate the assembly process on the Au(111) surface and the [12]CPP nanoring can change the weak van der Waals forces and influence self-assembly. Moreover, the electron spin in paramagnetic Y2@C79N was employed to percept the host–gues...

Metal-organic coordination structures at interfaces play an essential role in many biological and chemical systems. Understanding the molecular specificity, orientation and spatial distribution of the coordination complexes at the nanometer scale is of great im-portance for effective molecular engineering of nanostructures and fabrication of functional devices with controllable properties. However, fundamental properties of such coordination systems are still rarely studied directly. In this work, we present a spectro-scopic approach on the basis of tip-enhanced Raman spectroscopy (TERS) to investigate a cobalt(II) tetraphenyl-porphyrine (CoTPP) coordination species on the scale of a single molecule under ambient conditions. Coordination species anchored on gold surfaces modified with pyridine thiol self-assembled monolayers can be spectroscopically distinguished and mapped with ca. 2 nm resolution. In addition, in combination with density functional theory simulations, the adsorption configuration and molecular ori-entation of the coordination complexes are also revealed using TERS imaging.

We report a molecular investigation of a cobalt phthalocyanine (CoPc)-catalyzed CO

The in situ on-surface conversion process from boroxine-linked covalent organic frameworks (COFs) to boronate ester-linked COFs is triggered and catalyzed at room temperature by an electric field and monitored with scanning tunneling microscopy (STM). The adaptive behavior within the generated dynamic covalent libraries (DCLs) was revealed, providing in-depth understanding of the dynamic network switching process. ispartof: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY vol:142 issue:13 pages:5964-5968 ispartof: location:United States status: published

Understanding the mechanisms of electrocatalytic reactions is essential for development of lower cost, high-efficiency electrocatalysts for electrochemical energy conversion technology. The investigation of structures and reactions of electrocatalysts at electrode surfaces with a single molecular scale resolution benefits mechanism studies as well as catalysts development. This review summarizes recent studies on investigating the structure of electrocatalysts, distribution of catalytic active sites, and in-situ monitoring of electrocatalytic processes in reactions by scanning tunneling microscope. The challenge and future development in the field are also outlined.

A pyrene-cored molecular quadripod 1,3,6,8-tetra(di(p-pyrid-4-ylphenyl)amino)pyrene (TAPyr) is presented as a noncovalent interfacial coupling reagent for the immobilization of coordination assemblies. This bench-stable molecule is readily available and has a quadripod shape with four pyridine legs and four pyridine handles on the top exterior. By a simple and short dipping procedure under ambient conditions, TAPyr is firmly immobilized on electrode surfaces in an upright fashion as probed by electrochemical, absorption spectral, atomic force microscopy, and scanning tunneling microscopy analysis. Using Pd(PhCN)2Cl2 as a metallolinker, 4-ferrocenylpyridine, a pyridine-terminated monoruthenium complex 1, and a diruthenium complex 2 with two pyridine ends have been grafted onto the ITO/TAPyr surface. The obtained thin films exhibit good electrochemical stability that is comparable or superior to those prepared by the state-of-the-art Si–O–Sn covalent functionalization. Appealing electrochromism is demonstra...

Here we show a conceptual approach to realize the scanning tunneling microscopy based induced-assembly of fullerene (C60) molecules on top of a buffer organic adlayer at room temperature in a solution environment. The realization of spatially-defined C60 assembly is attributed to the modulation of substrate-molecular interactions with the assistance of a buffer layer.

We report the potential and concentration controlled assembly of an alkyl-substituted benzo[1,2-b:4,5-b']dithiophene (DDBDT) on an Au(111) electrode by in situ electrochemical scanning tunneling microscopy (ECSTM). It is found that a lamellar structure is formed at low concentrations, while herringbone-like and rhombus structures are obtained at high concentrations. In situ STM results reveal that herringbone-like and rhombus structures could transform into lamellar structures when the electrode potential is tuned negatively. A phase diagram is obtained to illustrate the relationship and effects of concentration and substrate potential on the interfacial structures of DDBDT. Both the substrate potential and the solute concentration can modulate the self-assembly structure through changing the molecular surface density. The results provide important insights into the understanding and precise control of molecular self-assembly on solid surfaces through a combination of different approaches.

The theory of quaternion differential equations (QDEs) has recently received a lot of attention. They have numerous applications in physics and engineering problems. In the present investigation, a new approach to solve the linear QDEs is achieved. Specifically, the solutions of QDEs with two-sided coefficients are studied via the adjoint matrix technique. That is, each quaternion can be uniquely expressed as a form of linear combinations of two complex numbers. By applying the complex adjoint representation of quaternion matrix, the connection between QDEs, with unilateral or two-sided coefficients, and a system of ordinary differential equations is achieved. By a novel specific algorithm, the solutions of QDEs with two-sided coefficients are fulfilled.

The theory of real quaternion differential equations has recently received more attention, but significant challenges remain the non-commutativity structure. They have numerous applications throughout engineering and physics. In the present investigation, the Laplace transform approach to solve the linear quaternion differential equations is achieved. Specifically, the process of solving a quaternion different equation is transformed to an algebraic quaternion problem. The Laplace transform makes solving linear ODEs and the related initial value problems much easier. It has two major advantages over the methods discussed in literature. The corresponding initial value problems can be solved without first determining a general solution. More importantly, a particularly powerful feature of this method is the use of the Heaviside functions. It is helpful in solving problems, which is represented by complicated quaternion periodic functions. Copyright © 2017 John Wiley & Sons, Ltd.

By using an oriented electric field in a scanning tunneling microscope, one can locally control the condensation of boronic acids at the liquid/solid interface. The phase transition between self-assembled molecular networks and covalent organic frameworks is controlled by changing the polarity of the applied bias. The electric-field-induced phase transformation is reversible under ambient conditions.

Here we applied ionic interactions as the driving force to fabricate well-ordered bicomponent assemblies by using two porphyrin ions equipped with oppositely-charged groups. Two kinds of bimolecular chessboard structures were successfully constructed on Au(111) and investigated by scanning tunneling microscopy (STM).

We have studied the self-assembly structure of meso-diphenyltetrathia [22]-annulene [2,1,2,1] (DPTTA) on highly oriented pyrolytic graphite (HOPG), Au(111), and single-layer graphene (SLG) modified Au(111) substrates. High resolution scanning tunneling microscopy (STM) reveals that DPTTA molecules pack into one dimensionally ordered row structure on graphene and HOPG surfaces, while assemble into two dimensional close-packed structure on Au(111) surface. We ascribe this difference to the effect of the substrate. The addition of C60 molecules on these DPTTA modified substrates further reveals that the structural difference in DPTTA adlayer can affect its ability to form donor-acceptor (D-A) hierarchical structure with C60 molecules. The results provide an example of substrate effect in self-assemblies of functional molecules, which is significant for the design of molecular based devices.

We report an in situ electrochemical scanning tunneling microscopy (ECSTM) investigation of the 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (CoTPP)-catalyzed oxygen reduction reaction (ORR). A highly ordered CoTPP adlayer is revealed on the Au(111) electrode. High-contrast adsorbed species are monitored in CoTPP adlayer in electrolyte containing oxygen, and are attributed to the formation of CoTPP–O2 complexes. In situ STM results reveal the sharp contrast changes upon switching the substrate potential to trigger the ORR. The results benefit the understanding of the catalytic role of metal porphyrins (MPs) in the ORR, which is important for the design of MP-based catalysts.

An understanding of the species of chlorine is crucial in the metropolis-Beijing, which is suffering serious haze pollution with high frequency. Particulate Matters (PMs) with five different sizes were collected in Beijing from July 2009 to March 2016, and characterized non-destructively by X-ray absorption near edge structure spectroscopy. PM 2.5 contributed for the major PMs mass in spring and summer, PM0.5-1.0 and PM1.0-2.5 contributed for the major PMs mass in autumn and winter. The concentrations of the three chlorine species were in the order of inorganic chlorine (Clinorg) > aliphatic chlorine (Clali) > aromatic chlorine (Claro), indicating that Clinorg constituted the primary chlorine fraction and less toxic Clali constituted the primary total organic chlorine (Clali + Claro, abbreviated as Clorg) in the PMs in Beijing. In addition, these three chlorine species exhibited identical seasonal variation in PM2.5: winter > autumn > spring > summer. Wet precipitation is an important factor to result in the lower mass concentrations of these three chlorine species in summer. The temporal variations of both size resolved PM mass concentrations and chlorine species concentrations suggested that the air pollution prevention and control in Beijing has just won initial success.

Two tetrachlorocuprate(II) salts, [4-RBzPy]2CuCl4 ([4-RBzPy]+ = 4-R-benzylpyridinium, R = Cl(1), NO2(2)), have been prepared and characterized by elemental analysis, IR, MS, single-crystal X-ray diffraction and magnetic susceptibility. Compound 1 crystallizes in the orthorhombic system with space group Pca21, while 2 in the monoclinic P21/c. Two salts comprise a tetrahedral [CuCl4]2− anion and two flexuous [4-RBzPy]+ cations. The cations both 1 and 2 form a column through p⋯π and π⋯π interactions, while the [CuCl4]2− anions only in 2 form a dimer through Cl⋯Cl interaction. The C–H⋯Cl and C–H⋯Cu weak hydrogen bonds between the anions and the cations give further rise to a 3D network structure. Magnetic susceptibility measurements in the temperature range 2–300 K show that 1 exhibits a ferromagnetic coupling behavior with θ = 3.57 K, while 2 shows an antiferromagnetism with J = −11.09 cm−1.

Metallothionein (MT) imprinted TiO2 membrane was synthesized via surface sol–gel process, using MT as template and TiO2 sol as imprinted matrix. Appropriate template cavities in the TiO2 sol–gel membrane were formed after the template molecules were removed on treatment with 1% NaOH solution. In situ technique of quartz crystal microbalance (QCM) was employed to study the molecular imprinting behavior of MT on nanocrystalline titania membranes. The imprinted membrane showed selectivity recognition for MT as compared to the other proteins. The amount of adsorption increased with the increasing of MT concentration both on imprinted membrane and non-imprinted membrane. The adsorption amount increased with the increasing of pH on imprinted membrane.