Intramolecular Coupling of Terminal Alkynes by Atom Manipulation

Double reactive oxygen species system photoinduced by Cu8 NCs: synergistic catalysis of phenylacetylene self-coupling reaction

Atomically precise nanoclusters (NCs) can serve as an excellent platform for a comprehensive understanding of structure-property relationships. Herein, three structurally similar Cu8 NCs (Cu8-1, Cu8-2 and Cu8-3) have been prepared for the photocatalytic phenylacetylene self-coupling reaction. It was found that Cu8-1 NC achieved the highest turnover number (TON) of 524.4, significantly higher than those of most reported catalysts. Herein, we propose a reasonable two-channel ROS participation mechanism by free radical scavenging and electron paramagnetic resonance (EPR) trapping experiments. This study provides a feasible strategy for exploring the photoinduced oxidative coupling of phenylacetylene, and provides a way for designing photocatalysts.

Advancements in π-Magnetism and Precision Engineering of Carbon-Based Nanostructures

The emergence of π-magnetism in low-dimensional carbon-based nanostructures, such as nanographenes (NGs), has captured significant attention due to their unique properties and potential applications in spintronics and quantum technologies. Recent advancements in on-surface synthesis under ultra-high vacuum conditions have enabled the atomically precise engineering of these nanostructures, effectively overcoming the challenges posed by their inherent strong chemical reactivity. This review highlights the essential concepts and synthesis methods used in studying NGs. It also outlines the remarkable progress made in understanding and controlling their magnetic properties. Advanced characterization techniques, such as scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM), have been instrumental in visualizing and manipulating these nanostructures, which highlighting their critical role in the field. The review underscores the versatility of carbon-based π-magnetic materials and their potential for integration into next-generation electronic devices. It also outlines future research directions aimed at optimizing their synthesis and exploring applications in cutting-edge technologies.

Modulating Copper Ladder Spacing in Copper Phenylacetylide for Enhanced Photocatalysis via Substituent Control

Copper phenylacetylide (PACu) is a promising photocatalyst due to its unique copper ladder (CL) electron transport channel, which facilitates efficient charge transfer. However, the structure-activity relationship between the CL spacing and its catalytic performance has yet to be revealed. In this study, we skillfully selected multiple substituents to regulate the CL spacing of the PACu photocatalyst. Our findings indicate that reducing the CL spacing significantly enhances carrier separation and transport efficiency, leading to improved oxygen adsorption and activation. Specifically, PACu-F demonstrated superior photocatalytic activity, achieving a 99% conversion rate in benzylamine oxidation and maintaining an excellent stability over multiple cycles. This study confirms the feasibility of tuning the CL spacing in PACu using donor/acceptor substituents to achieve a high-efficiency photocatalytic performance, offering crucial insights into the rational design of advanced photocatalysts.

On the CO2 Harvesting from N2 Using Grazyne Membranes

The separation of carbon dioxide (CO2) from nitrogen (N2) is at the core of any global warming remediation technology aimed at reducing the CO2 content in the atmosphere. Chemical membranes designed to differentially permeate both molecules have become quite appealing due to their simple use, although many membrane-based separations stand out as a promising solution for CO2 separation. These are environmentally friendly, with high active surface areas, compact design, easy to maintain and cost-effective, although the field is still growing due to the difficulties in the CO2/N2 separation. The present study poses grazynes, two-dimensional C-based materials with sp and sp2 C atoms, aligned along stripes, as suited membranes for the CO2/N2 separation. The combination of density functional theory (DFT) and molecular dynamics (MD) simulations allow tackling the energetics, kinetics, and dynamics of the membrane effectiveness of grazynes with engineered pores for such a separation in a holistic fashion. The explored grazynes are capable of physisorbing CO2 and N2, thus avoiding material poisoning by molecular decoration, while the diffusion of CO2 through the pores is found to be rapid, yet easier than that of N2, in the rate order of the s-1 in the 100-500 K temperature range. In particular, low-temperature CO2 separation even for CO2 contents below 0.5 % are found for [1],[2]{2}-grazyne when controlling the membrane exposure contact to the gas mixture, paving the way for exploring and using grazynes for air CO2 remediation.

Dramatic Acceleration of the Hopf Cyclization on Gold(111): From Enediynes to Peri-Fused Diindenochrysene Graphene Nanoribbons

Hopf et al. reported the high-temperature 6π-electrocyclization of cis-hexa-1,3-diene-5-yne to benzene in 1969. Subsequent studies using this cyclization have been limited by its very high reaction barrier. Here, we show that the reaction barrier for two model systems, (E)-1,3,4,6-tetraphenyl-3-hexene-1,5-diyne (1a) and (E)-3,4-bis(4-iodophenyl)-1,6-diphenyl-3-hexene-1,5-diyne (1b), is decreased by nearly half on a Au(111) surface. We have used scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) to monitor the Hopf cyclization of enediynes 1a,b on Au(111). Enediyne 1a undergoes two sequential, quantitative Hopf cyclizations, first to naphthalene derivative 2, and finally to chrysene 3. Density functional theory (DFT) calculations reveal that a gold atom from the Au(111) surface is involved in all steps of this reaction and that it is crucial to lowering the reaction barrier. Our findings have important implications for the synthesis of novel graphene nanoribbons. Ullmann-like coupling of enediyne 1b at 20 °C on Au(111), followed by a series of Hopf cyclizations and aromatization reactions at higher temperatures, produces nanoribbons 12 and 13. These results show for the first time that graphene nanoribbons can be synthesized on a Au(111) surface using the Hopf cyclization mechanism.

A Simple and Practical Bis-N-Heterocyclic Carbene as an Efficient Ligand in Cu-Catalyzed Glaser Reaction

Conjugated diyne derivatives are important scaffolds in modern organic synthetic chemistry. Using the Glaser reaction involves the coupling of terminal alkynes which can efficiently produce conjugated diyne derivatives, while the use of a stoichiometric amount of copper salts, strong inorganic base, and excess oxidants is generally needed. Developing an environmentally friendly and effective method for the construction of symmetrical 1,3-diynes compounds by Glaser coupling is still highly desirable. In this study, we present an economical method for the production of symmetric diynes starting from various terminal acetylenes in a Glaser reaction. A simple and practical bis-N-heterocyclic carbene ligand has been introduced as efficient ligands for the Cu-catalyzed Glaser reaction. High product yields were obtained at 100 °C for a variety of substrates including aliphatic and aromatic terminal alkynes and differently substituted terminal alkynes including the highly sterically hindered substrate 2-methoxy ethynylbenzene or 2-trifluoromethyl ethynylbenzene and a series of functional groups, such as trifluoromethyl group, ester group, carboxyl group, and nitrile group. The established protocol is carried out in air under base-free condition and is operationally simple. These research work suggest that bis-N-heterocyclic carbene could also an appealing ligand for Glaser reaction and provide a reference for the preparation of symmetric 1,3-diynes in industrial filed.

Dielectric behavior of curcuminoid polymorphs on different substrates by direct soft vacuum deposition

Our work examines the structural-electronic correlation of a new curcuminoid, AlkCCMoid, as a dielectric material on different substrates. For this purpose, we show a homemade sublimation method that allows the direct deposition of molecules on any type of matrix. The electronic properties of AlkCCMoid have been evaluated by measurements on single crystals, microcrystalline powder, and sublimated samples, respectively. GIWAXS studies on surfaces and XRD studies on powder have revealed the existence of polymorphs and the effect that substrates have on curcuminoid organization. We describe the dielectric nature of our system and identify how different polymorphs can affect electronic parameters such as permittivity, all corroborated by DFT calculations.

Converting n-Alkanol to Conjugated Polyenal on Cu(110) Surface at Mild Temperature

Achieving C(sp³)-H activation at a mild temperature is of great importance from both scientific and technologic points of view. Herein, on the basis of the on-surface synthesis strategy, we report the significant reduction of the C(sp³)-H activation barrier, which results in the full C(sp³)-H to C(sp²)-H transformation of n-alkanol (octacosan-1-ol) at a mild temperature as low as 350 K on the Cu(110) surface, yielding the conjugated polyenal (octacosa-tridecaenal) as the final product. The reaction mechanism is revealed by the combined scanning tunneling microscope, density functional theory, and synchrotron radiation photoemission spectroscopy.

Constructing covalent organic nanoarchitectures molecule by molecule via scanning probe manipulation

Constructing low-dimensional covalent assemblies with tailored size and connectivity is challenging yet often key for applications in molecular electronics where optical and electronic properties of the quantum materials are highly structure dependent. We present a versatile approach for building such structures block by block on bilayer sodium chloride (NaCl) films on Cu(111) with the tip of an atomic force microscope, while tracking the structural changes with single-bond resolution. Covalent homo-dimers in cis and trans configurations and homo-/hetero-trimers were selectively synthesized by a sequence of dehalogenation, translational manipulation and intermolecular coupling of halogenated precursors. Further demonstrations of structural build-up include complex bonding motifs, like carbon–iodine–carbon bonds and fused carbon pentagons. This work paves the way for synthesizing elusive covalent nanoarchitectures, studying structural modifications and revealing pathways of intermolecular reactions.

Tailoring the size and connectivity of organic nanostructures is challenging but is often key in molecular electronics for tuning the properties of the quantum materials. Now an approach has been developed for building low-dimensional covalent architectures block by block on a surface by highly selective tip-induced intermolecular reactions.

Benchmarking atomically defined AFM tips for chemical-selective imaging

Controlling the identity of the tip-terminating atom or molecule in low-temperature atomic force microscopy has led to ground breaking progress in surface chemistry and nanotechnology. Lacking a comparative tip-performance assessment, a profound standardization in such experiments is highly desirable. Here we directly compare the imaging and force-spectroscopy capabilities of four atomically defined tips, namely Cu-, Xe-, CO-, and O-terminated Cu-tips (CuOx-tips). Using a nanostructured copper-oxide surface as benchmark system, we found that Cu-tips react with surface oxygen, while chemically inert Xe- and CO-tips allow entering the repulsive force regime enabling increased resolution. However, their high flexibility leads to imaging artifacts and their strong passivation suppresses the chemical contrast. The higher rigidity and selectively increased chemical reactivity of CuOx-tips prevent tip-bending artifacts and generate a distinct chemical contrast. This result is particularly promising in view of future studies on other metal-oxide surfaces.

A single-molecule blueprint for synthesis

Chemical reactions that occur at nanostructured electrodes have garnered widespread interest because of their potential applications in fields including nanotechnology, green chemistry and fundamental physical organic chemistry. Much of our present understanding of these reactions comes from probes that interrogate ensembles of molecules undergoing various stages of the transformation concurrently. Exquisite control over single-molecule reactivity lets us construct new molecules and further our understanding of nanoscale chemical phenomena. We can study single molecules using instruments such as the scanning tunnelling microscope, which can additionally be part of a mechanically controlled break junction. These are unique tools that can offer a high level of detail. They probe the electronic conductance of individual molecules and catalyse chemical reactions by establishing environments with reactive metal sites on nanoscale electrodes. This Review describes how chemical reactions involving bond cleavage and formation can be triggered at nanoscale electrodes and studied one molecule at a time.

Chemical Identification and Bond Control of π-Skeletons in a Coupling Reaction

Highly unsaturated π-rich carbon skeletons afford versatile tuning of structural and optoelectronic properties of low-dimensional carbon nanostructures. However, methods allowing more precise chemical identification and controllable integration of target sp-/sp²-carbon skeletons during synthesis are required. Here, using the coupling of terminal alkynes as a model system, we demonstrate a methodology to visualize and identify the generated π-skeletons at the single-chemical-bond level on the surface, thus enabling further precise bond control. The characteristic electronic features together with localized vibrational modes of the carbon skeletons are resolved in real space by a combination of scanning tunneling microscopy/spectroscopy (STM/STS) and tip-enhanced Raman spectroscopy (TERS). Our approach allows single-chemical-bond understanding of unsaturated carbon skeletons, which is crucial for generating low-dimensional carbon nanostructures and nanomaterials with atomic precision.

Reassessing Alkyne Coupling Reactions While Studying the Electronic Properties of Diverse Pyrene Linkages at Surfaces

The combination of alkyne and halogen functional groups in the same molecule allows for the possibility of many different reactions when utilized in on-surface synthesis. Here, we use a pyrene-based precursor with both functionalities to examine the preferential reaction pathway when it is heated on an Au(111) surface. Using high-resolution bond-resolving scanning tunneling microscopy, we identify multiple stable intermediates along the prevailing reaction pathway that initiate with a clearly dominant Glaser coupling, together with a multitude of other side products. Importantly, control experiments with reactants lacking the halogen functionalization reveal the Glaser coupling to be absent and instead show the prevalence of non-dehydrogenative head-to-head alkyne coupling. We perform scanning tunneling spectroscopy on a rich variety of the product structures obtained in these experiments, providing key insights into the strong dependence of their HOMO-LUMO gaps on the nature of the intramolecular coupling. A clear trend is found of a decreasing gap that is correlated with the conversion of triple bonds to double bonds via hydrogenation and to higher levels of cyclization, particularly with nonbenzenoid product structures. We rationalize each of the studied cases.

On-Surface Synthesis and Intermolecular Cycloadditions of Indacenoditetracenes, Antiaromatic Analogues of Undecacene

The formation of s-indaceno[1,2-b:5,6-b']ditetracene and as-indaceno[2,3-b:6,7-b']ditetracene containing indenofluorene cores from a common precursor has been achieved by a dehydrogenative surface-assisted cyclization on Au(111) and confirmed by bond-resolved non-contact atomic force microscopy. On-surface generated as-indaceno[2,3-b:6,7-b']ditetracenes undergo fusion, which leads to T-shaped adducts by an intermolecular cycloaddition. The same type of cycloaddition, which has no parallel in solution chemistry, has been observed between as-indaceno[2,3-b:6,7-b']ditetracene and pentacene or octacene. These examples of surface-assisted cycloaddition provide perspectives for the rational design and synthesis of molecular nanostructures.

Intramolecular Coupling of Terminal Alkynes by Atom Manipulation

Glaser-like coupling of terminal alkynes by thermal activation is extensively used in on-surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser-like coupling between terminal alkyne carbons within a custom-synthesized precursor molecule adsorbed on bilayer NaCl on Cu(111). Different conformations of the precursor molecule and the product were characterized by molecular structure elucidation with atomic force microscopy and orbital density mapping with scanning tunneling microscopy, accompanied by density functional theory calculations. We revealed partially dehydrogenated intermediates, providing insight into the reaction pathway.