The forming processes of 4,40-dipyridyl-based single-molecule junctions and mechanically induced conductance switching as well as the side-group effects are systematically investigated by applying the ab initio-based ...The forming processes of 4,40-dipyridyl-based single-molecule junctions and mechanically induced conductance switching as well as the side-group effects are systematically investigated by applying the ab initio-based adiabatic geometric optimization method and the one-dimensional transmission combined with three-dimensional correction approximation(OTCTCA)method.The numerical results show that for the 4,40-dipyridyl with a p-conjugated phenyl-phosphoryl or diphenylsilyl side group,the pyridyl vertically anchors on the second atomic layer of the pyramid-shaped Au tip electrode at small inter-electrode distances by laterally pushing the apical Au atom aside,which induces stronger pyridyl-electrode coupling and high-conductance state of the formed junctions.As the inter-electrode distance increases,the pyridyl shifts to the apical Au atom of the tip electrode.This apical Au atom introduces additional scatterings to the tunneling electrons and significantly decreases the conductance of the junctions.Furthermore,for the 4,40-dipyridyl with a phenyl-phosphoryl side group,the probability of manifesting the high-conductance state is decreased due to the oxygen atom reducing the probability of the pyridyl adsorbing on the second layer of Au tip electrode.In contrast,for the 4,40-dipyridyl with a nonconjugated cyclohexyl-phosphoryl side group,the steric hindrance from the bulky cyclohexyl group leads the molecule to preferentially form the O-Au contact,which prevents both the high conductance and mechanically induced conductance switching of the junction.Our results provide a theoretical understanding of the side-group effects on electronic transport properties of single-molecule junctions,offering an alternative explanation for the experimental observations.展开更多
Transition metal possesses a unique d-orbital electronic structure,which imparts a diverse range of physical and chemical properties.These properties render them significant in fields such as chemistry and materials s...Transition metal possesses a unique d-orbital electronic structure,which imparts a diverse range of physical and chemical properties.These properties render them significant in fields such as chemistry and materials science.The distinctive optical,electrical,and magnetic properties of these complexes can be attributed to the variations in the quantity of d-orbital electrons,thereby influencing their spin and orbital characteristics.The d-orbitals facilitate the formation of stable multidirectional bonds with ligands,resulting in a variety of geometric structures and rich coordination chemistry.These interactions result in variations in energy levels,thereby producing diverse electrical properties,including low attenuation coefficients,high rectification ratios,and unique multichannel transmission.Moreover,the unpaired electrons inthe d-orbitals can give rise to diverse magnetic behaviors,leading to magnetic effects such as spin-related interfaces,switches,and magnetoresistance.This paves the way for extensive possibilities in the design and application of single-molecule devices.This review elaborates on singlemolecule physical properties of transition metal complexes,including length attenuation,rectification,multi-channel transmission,thermoelectric effect,and spin regulation,which are vital for the functionalization and regulation of molecular electronics.In addition,this review also explores the correlation between these physical properties and the electronic structure of transition metals,discussing the broad prospects of transition metal complexes in the fields of nanoelectronics,optoelectronics,and quantum technology.展开更多
Single-molecule junctions,integrating individual molecules as active components between electrodes,serve as fundamental building blocks for advanced electronic and sensing technologies.The application of ionic liquids...Single-molecule junctions,integrating individual molecules as active components between electrodes,serve as fundamental building blocks for advanced electronic and sensing technologies.The application of ionic liquids in single-molecule junctions represents a cutting-edge and rapidly evolving field of research at the intersection of nanoscience,materials chemistry,and electronics.This review explores recent advances where ionic liquids function as electrolytes,dielectric layers,and structural elements within single-molecule junctions,reshaping charge transport,redox reactions,and molecular behaviors in these nanoscale systems.We comprehensively dissect fundamental concepts,techniques,and modulation mechanisms,elucidating the roles of ionic liquids as gates,electrochemical controllers,and interface components in singlemolecule junctions.Encompassing applications from functional device construction to unraveling intricate chemical reactions,this review maps the diverse applications of ionic liquids in single-molecule junctions.Moreover,we propose critical future research topics in this field,including catalysis involving ionic liquids at the single-molecule level,functionalizing single-molecule devices using ionic liquids,and probing the structure and interactions of ionic liquids.These endeavors aim to drive technological breakthroughs in nanotechnology,energy,and quantum research.展开更多
Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions.Here,using the first-principles method,we theoretically investigate spin transport properties and p...Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions.Here,using the first-principles method,we theoretically investigate spin transport properties and photoresponse characteristics in trimesic acid magnetic single-molecule junctions with different molecular adsorption orientations and electrode contact sites.The transport calculations indicate that a single-molecule switch and a significant enhancement of spin transport and photoresponse can be achieved when the molecular adsorption orientation changes from planar geometry to upright geometry.The maximum spin polarization of current and photocurrent in upright molecular junctions exceeds 90%.Moreover,as the Ni tip electrode moves,the tunneling magnetoresistance of upright molecular junctions can be increased to 70%.The analysis of the spin-dependent PDOS elucidates that the spinterfaces between organic molecule and ferromagnetic electrodes are modulated by molecular adsorption orientation,where the molecule in upright molecular junctions yields higher spin polarization.Our theoretical work paves the way for designing spintronic devices and optoelectronic devices with anisotropic functionality base on anisotropic molecules.展开更多
Clustering is a pivotal data analysis method for deciphering the charge transport properties of single molecules in break junction experiments.However,given the high dimensionality and variability of the data,feature ...Clustering is a pivotal data analysis method for deciphering the charge transport properties of single molecules in break junction experiments.However,given the high dimensionality and variability of the data,feature extraction remains a bottleneck in the development of efficient clustering methods.In this regard,extensive research over the past two decades has focused on feature engineering and dimensionality reduction in break junction conductance.However,extracting highly relevant features without expert knowledge remains an unresolved challenge.To address this issue,we propose a deep clustering method driven by task-oriented representation learning(CTRL)in which the clustering module serves as a guide for the representation learning(RepL)module.First,we determine an optimal autoencoder(AE)structure through a neural architecture search(NAS)to ensure efficient RepL;second,the RepL process is guided by a joint training strategy that combines AE reconstruction loss with the clustering objective.The results demonstrate that CTRL achieves excellent performance on both the generated and experimental data.Further inspection of the RepL step reveals that joint training robustly learns more compact features than the unconstrained AE or traditional dimensionality reduction methods,significantly reducing misclustering possibilities.Our method provides a general end-to-end automatic clustering solution for analyzing single-molecule break junction data.展开更多
Gaining insights into charge transport related to conformational changes and ion transport in valinomycin(VM)is crucial for understanding the underlying physiological processes and advancing ion carrier applications.O...Gaining insights into charge transport related to conformational changes and ion transport in valinomycin(VM)is crucial for understanding the underlying physiological processes and advancing ion carrier applications.Observing these processes in single molecules provides deeper insights and precision than those obtained through conventional ensemble measurements.Herein,we employed a single-molecule conductance measurement method based on the scanning tunneling microscopy break-junction(STM-BJ)to measure the charge transport of individual VM molecules in both non-polar and polar solvents,as well as when mediated by K^(+)ions.Single-molecule conductance measurements revealed that the bracelet and propeller-type conformations of VM in both non-polar and polar solvents significantly affect its conductance.In polar solvents,the propeller-type conformation of VM demonstrated a well-defined conductance signature,single-molecule rectification feature,and through-space transmission mechanism.Specifically,the introduction of K^(+)ions in polar solvents induced a conformational transition from the propeller-type to the bracelet-type form,facilitating K^(+)binding recognition.These observations were further supported by density functional theory combined with non-equilibrium Green’s function calculations.This study enhanced the fundamental understanding of the electronic transport mechanisms in VM and valinomycin-K^(+)molecular junctions,offering insights into VM ionophores and promoting supramolecular sensing applications.展开更多
π-πstacking,a fundamental noncovalent interaction between aromatic molecules,is essential for enabling charge transport across molecular fragments a process vital to both chemistry and biology.^(1,2)Owing to the wid...π-πstacking,a fundamental noncovalent interaction between aromatic molecules,is essential for enabling charge transport across molecular fragments a process vital to both chemistry and biology.^(1,2)Owing to the widespread importance ofπ-πinteractions in diverse fields,there is considerable interest in precisely modulating the interaction at the single-molecule scale.Studies have shown thatπ-πinteraction can be influenced by adjusting molecular concentration,^(3) applying mechanical forces,^(4) or designing target molecules with enhanced attraction.^(5)However,achieving precise control of intermolecularπ-πinteraction at the single-molecule level without altering molecular conformation or concentration remains a significant challenge.展开更多
Single-molecule electrical and spin switches have been one of the main research focuses in molecular electronics and spintronics because they may form the most important elements for the future information technology,...Single-molecule electrical and spin switches have been one of the main research focuses in molecular electronics and spintronics because they may form the most important elements for the future information technology,thus attracting great attention in the scientific community and witnessing significant progresses benefiting from the combination of physics,chemistry,materials,and engineering.The key issue of constructing single-molecule switches is the development of stimulus-responsive systems that provide bistable or multiple states.In this review,we summarize the recent advances of this field in terms of the external stimulus that induces the switching.A variety of external stimuli,such as light,electric field,magnetic field,mechanical force,and chemical stimulus,have been successfully employed to activate the reversible switching in single-molecule junctions by manipulating molecular structures,conformations,electronic states,and spin states.As a burgeoning field,we finally put forward the challenges in molecular electronics and spintronics that need to be solved,which will initiate intense research.展开更多
The investigation of electronic excited states in single-molecule junctions not only provides platforms to reveal the photophysical and photochemical processes at the molecular level,but also brings opportunities for ...The investigation of electronic excited states in single-molecule junctions not only provides platforms to reveal the photophysical and photochemical processes at the molecular level,but also brings opportunities for the development of single-molecule optoelectronic devices.Understanding the interaction mechanisms between molecules and nanocavities is essential to obtain ondemand properties in devices by artificial design,since molecules in junctions exhibit unique behaviors of excited states benefited from the structures of metallic nanocavities.Here,we review the excitation mechanisms involved in the interplay between molecules and plasmonic nanocavities,and reveal the influence of nanostructures on excited-state properties by demonstrating the differences in excited state decay processes.Furthermore,vibronic transitions of molecules between nanoelectrodes are also discussed,offering a new single-molecule characterization method.Finally,we provide the potential applications and challenges in single-molecule optoelectronic devices and the possible directions in exploring the underlying mechanisms of photophysical and photochemical processes.展开更多
Electronic coupling between individual building blocks plays an essential role in charge transport through molecular materials and devices.However,the investigation of the transmission mechanism in charge transport vi...Electronic coupling between individual building blocks plays an essential role in charge transport through molecular materials and devices.However,the investigation of the transmission mechanism in charge transport via intramolecular coupling remains challenging.Herein,we demonstrate the transition of the intramolecular through-bond and through-space coupling in a single-molecule junction with a family of diketopyrrolopyrrole(DPP)derivative by varying intramolecular donor–acceptor(D–A)interactions.The transition is accomplished by regulating D–A interactions by inserting different aromatic rings inside,leading to two orders of magnitude difference of the single-molecule conductance.The flicker noise analysis demonstrates that the conductance difference arises from the control of the contribution between through-bond and through-space coupling.These findings are further supported by the calculation that the intramolecular coupling among molecular building blocks correlates with the D–A interaction,providing a promising way to regulate the contribution between through-bond and through-space coupling in the charge transport through molecular materials and devices.展开更多
The electronic structure of semiconductor materials governs the law of electron motion,which profoundly affects the properties such as conductivity and photoelectric conversion.Photo-responsive single-molecule junctio...The electronic structure of semiconductor materials governs the law of electron motion,which profoundly affects the properties such as conductivity and photoelectric conversion.Photo-responsive single-molecule junction technology provides insights into the electronic structure of photogenerated substances at the molecular scale,enabling the characterization of dynamic processes such as charge separation and energy transfer.These processes involve the unique quantum state known as the "exciton".The electrical characterization technique based on single molecule break junction facilities direct measurement of the photoelectric response of molecules at nanometer and subnanometer scale.This study reviews recent research progress of exciton effects and the characterization of optoelectronic phenomena.The mechanisms of exciton effects in three key optoelectronic phenomena—photoconductivity,photovoltaic s,and photoluminescence—are discussed.Furthermore,advanced spectral characterization techniques applied to the in-situ monitoring of single-molecule optoelectronic devices are highlighted.These include Raman spectroscopy with various enhancements,inelastic electron tunneling spectroscopy,and ultrafast spectroscopy with high resolution.展开更多
Quantum interference(QI)effects,which offer unique opportunities to widely manipulate the charge transport properties in the molecular junctions,will have the potential for achieving high thermopower.Here we developed...Quantum interference(QI)effects,which offer unique opportunities to widely manipulate the charge transport properties in the molecular junctions,will have the potential for achieving high thermopower.Here we developed a scanning tunneling microscope break junction technique to investigate the thermopower through single-molecule thiophene junctions.We observed that the thermopower of 2,4-TPSAc with destructive quantum interference(DQI)was nearly twice of 2,5-TP-SAc without DQI,while the conductance of the 2,4-TP-SAc was two orders of magnitude lower than that of 2,5-TP-SAc.Furthermore,we found the thermopower was almost the same by altering the anchoring group or thiophene core in the control experiments,suggesting that the QI effect is responsible for the increase of thermopower.The density functional theory(DFT)calculations are in quantitative agreement with the experimental data.Our results reveal that QI effects can provide a promising platform to enhance the thermopower of molecular junctions.展开更多
Hydrogen bonding is a vital driving force for organizing the hierarchy of molecular structure,especially in biologic field.Due to its directionality,selectivity and moderate strength,hydrogen bonding has been extensiv...Hydrogen bonding is a vital driving force for organizing the hierarchy of molecular structure,especially in biologic field.Due to its directionality,selectivity and moderate strength,hydrogen bonding has been extensively introduced into the molecular recognition,sensing and electronic devices.Electric measurements at single-molecule level facilitate the investigation of hydrogen bonds and provide a comprehensive understanding of the electron transport properties governed by the hydrogen bonding,which is essential for the development of self-assembled electronic systems.This review provides a detailed overview of recent advancements in constructing single-molecule junctions utilizing intramolecular and intermolecular hydrogen bonding.We first introduce the methods utilized for characterizing the electric and dynamic properties of non-covalent interactions.Next,we discuss the mechanisms of electron transport,relevant influencing factors,and typical applications utilizing electrical signals based on single-molecule junctions.Finally,we propose our perspective on the existing challenges and prospective opportunities in utilizing hydrogen bonding for electronic device applications.展开更多
Investigating the quantum interference effect in single molecules is essential to comprehensively understand the underlying mechanism of single-molecule charge transport.In this study,we employed the mother molecule m...Investigating the quantum interference effect in single molecules is essential to comprehensively understand the underlying mechanism of single-molecule charge transport.In this study,we employed the mother molecule m-OPE and introduced a series of side groups with various electronic effects at the 2-position of the central phenyl ring,creating four daughter m-OPE derivatives.The single molecular conductivities of these molecule wires were measured using the scanning tunneling microscope breaking junction technique.Our findings demonstrate that the substitutions regularly modulate the destructive quantum interference occurring within the m-OPE molecules.By combining optical and electrochemical investigations,along with density functional theory computations,we discover that the conductivity of the molecules corresponds to the electron-donating/withdrawing ability of the substituents.Specifically,by adjusting the electron structures of the molecular backbone,we can systematically tailor the destructive quantum interference in the m-OPE molecules.展开更多
To monitor and investigate chemical reactions in real time and in situ is a long-standing,challenging goal in chemistry.Herein,an electric potential-promoted oxidative coupling reaction of organoboron compounds withou...To monitor and investigate chemical reactions in real time and in situ is a long-standing,challenging goal in chemistry.Herein,an electric potential-promoted oxidative coupling reaction of organoboron compounds without the addition of base is reported,and the transmetallation process involved is monitored in real time and in situ with the scanning tunneling microscopy break single-molecule junctions(STMBJ)technique.We found that the electric potential applied determined the transmetallation.At low-bias voltage,the first-step transmetallation process occurred and afforded Au─C-bonded aryl gold intermediates.The electronic properties of organoboron compounds have a strong influence on the transmetallation process,and electron-rich compounds facilitate this transformation.At high-bias voltage,the second-step transmetallation process took place,and the corresponding intermediate(highly reactive diaryl metal complex)was detected with the assistance of Pd(OAc)_(2).Our work demonstrates the applications of STMBJ on in situ monitoring and catalyzing of chemical reactions and provides a new methodology to fabricate singlemolecule devices.展开更多
Raman spectroscopy offers a great power to detect,analyze and identify molecules,and monitor their temporal dynamics and evolution when combined with single-molecule surface-enhanced Raman scattering(SM-SERS)substrate...Raman spectroscopy offers a great power to detect,analyze and identify molecules,and monitor their temporal dynamics and evolution when combined with single-molecule surface-enhanced Raman scattering(SM-SERS)substrates.Here we present a SM-SERS scheme that involves simultaneously giant chemical enhancement from WS22D materials,giant electromagnetic enhancement from plasmonic nanogap hot spot,and inhibition of molecular fluorescence influence under near-infrared laser illumination.Remarkably we find Coulomb attraction between analyte and gold nanoparticle can trigger spontaneous formation of molecule-hotspot pairing with high precision,stability and robustness.The scheme has enabled realization of universal,robust,fast,and large-scale uniform SM-SERS detection for three Raman molecules of rhodamine B,rhodamine 6G,and crystal violet with a very low detection limit of 10−16 M and at a very fast spectrum acquisition time of 50 ms.展开更多
The quantum interference effect in the charge transport through single-phenyl molecules received intensive interests from theory but remained as an experimental challenge. In this paper, we investigated the charge tra...The quantum interference effect in the charge transport through single-phenyl molecules received intensive interests from theory but remained as an experimental challenge. In this paper, we investigated the charge transport through single-molecule benzene dithiol （BDT） junction with different connectivities using mechanically controllable break.junction （MCB]） technique. By further improving the mechanical stability and the electronic measuring component of the MCBJ set-up, we obtained the conductance histograms of BDT molecules （BDTs） from the statistical analysis of conductance-distance traces without data selection. By tuning the connectivity, the conductance of BDTs is determined to be 10-12Go, 10-22Go and 10-10Go for pcra, meta, and ortho connectivity, following the trend that ortfio-BDT 〉 para-BDT 〉 meta-BDT. Furthermore, the displacements of the junctions followed the trend that para 〉 meta 〉 ortho, suggesting the charge transport through the molecules via the gold-thiol bond. The different trends between conductance and displacement for different connectivities suggests the presence of destructive quantum interference effect on meta-BDT, which provides the experimental evidence for the quantum interference effect through single-phenyl molecular junctions.展开更多
Quinoid structures are considered to be conducive to the charge transport of organic molecules,but this hypothesis is rarely proven at single-molecule level.Herein,as a proof of concept,the single-molecule conductance...Quinoid structures are considered to be conducive to the charge transport of organic molecules,but this hypothesis is rarely proven at single-molecule level.Herein,as a proof of concept,the single-molecule conductance of two furan-based isomers,3,3'-bis(4-(methylthio)phenyl)-2,2'-bifuran(2,2'-SMPBF)and 4,4'-bis(4-(methylthio)phenyl)-3,3'-bifuran(3,3'-SMPBF),is investigated by the scanning tunneling microscopy break junction(STM-BJ)technique and theoretical simulation.2,2'-SMPBF prefers to adopt a nearly planar conformation with intact alternating single and double bonds extended via2,2'-bifuran moiety and therefore exhibits goodπ-conjugation and a prominent quinoid structure.However,theπ-conjugation of 3,3'-SMPBF is interrupted due to ineffective cross-conjugation in the 3,3'-bifuran moiety,leading to the absence of a quinoid structure.2,2'-SMPBF displays switchable multiple conductances induced by the interconversion between folded and unfolded conformations and an abnormal rebound of conductance along with the increases of electrode displacement,which is demonstrated to be caused by the quinoid structure in a nearly planar conformation during the stretching process.However,3,3'-SMPBF without a quinoid structure in unfolded conformation exhibits extremely low conductance that cannot be captured in STM-BJ measurements.These results reveal the significant contribution of quinoid structure to molecular charge transport and provide valuable information on the structure-transport relationship for the design of efficient organic semiconductors.展开更多
State-of-the-art molecular electronics focus on the measurement of electrical properties of materials at the single-molecule level.Experimentally, molecular electronics face two primary challenges. One challenge is th...State-of-the-art molecular electronics focus on the measurement of electrical properties of materials at the single-molecule level.Experimentally, molecular electronics face two primary challenges. One challenge is the reliable construction of single-molecule junctions, and the second challenge is the arbitrary modulation of electron transport through these junctions. Over the past decades, electrochemistry has been widely adopted to meet these challenges, leading to a wealth of novel findings. This review starts from the application of electrochemical methods to the fabrication of nanogaps, which is an essential platform for the construction of single-molecule junctions. The utilization of electrochemistry for the modification of molecular junctions,including terminal groups and structural backbones, is introduced, and finally, recent progress in the electrochemical modulation of single-molecule electron transport is reviewed.展开更多
To explore solvent gating of single-molecule electrical conductance due to solvent-molecule interactions, charge transport through single-molecule junctions with different anchoring groups in various solvent environme...To explore solvent gating of single-molecule electrical conductance due to solvent-molecule interactions, charge transport through single-molecule junctions with different anchoring groups in various solvent environments was measured by using the mechanically controllable break junction technique. We found that the conductance of single-molecule junctions can be tuned by nearly an order of magnitude by varying the polarity of solvent. Furthermore, gating efficiency due to solvent–molecule interactions was found to be dependent on the choice of the anchor group. Theoretical calculations revealed that the polar solvent shifted the molecular-orbital energies, based on the coupling strength of the anchor groups. For weakly coupled molecular junctions, the polar solvent–molecule interaction was observed to reduce the energy gap between the molecular orbital and the Fermi level of the electrode and shifted the molecular orbitals. This resulted in a more significant gating effect than that of the strongly coupled molecules. This study suggested that solvent–molecule interaction can significantly affect the charge transport through single-molecule junctions.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12474286,22173052,and 12204281).
文摘The forming processes of 4,40-dipyridyl-based single-molecule junctions and mechanically induced conductance switching as well as the side-group effects are systematically investigated by applying the ab initio-based adiabatic geometric optimization method and the one-dimensional transmission combined with three-dimensional correction approximation(OTCTCA)method.The numerical results show that for the 4,40-dipyridyl with a p-conjugated phenyl-phosphoryl or diphenylsilyl side group,the pyridyl vertically anchors on the second atomic layer of the pyramid-shaped Au tip electrode at small inter-electrode distances by laterally pushing the apical Au atom aside,which induces stronger pyridyl-electrode coupling and high-conductance state of the formed junctions.As the inter-electrode distance increases,the pyridyl shifts to the apical Au atom of the tip electrode.This apical Au atom introduces additional scatterings to the tunneling electrons and significantly decreases the conductance of the junctions.Furthermore,for the 4,40-dipyridyl with a phenyl-phosphoryl side group,the probability of manifesting the high-conductance state is decreased due to the oxygen atom reducing the probability of the pyridyl adsorbing on the second layer of Au tip electrode.In contrast,for the 4,40-dipyridyl with a nonconjugated cyclohexyl-phosphoryl side group,the steric hindrance from the bulky cyclohexyl group leads the molecule to preferentially form the O-Au contact,which prevents both the high conductance and mechanically induced conductance switching of the junction.Our results provide a theoretical understanding of the side-group effects on electronic transport properties of single-molecule junctions,offering an alternative explanation for the experimental observations.
基金financially supported by the National Key R&D Program of China(Nos.2021YFA1200102,2021YFA1200101,2023YFF1205803,2022YFE0128700)the National Natural Science Foundation of China(Nos.22173050,22150013,21727806,21933001)+1 种基金Beijing National Laboratory for Molecular Sciences(No.BNLMS-CXXM-202407)the Natural Science Foundation of Beijing(No.2222009)
文摘Transition metal possesses a unique d-orbital electronic structure,which imparts a diverse range of physical and chemical properties.These properties render them significant in fields such as chemistry and materials science.The distinctive optical,electrical,and magnetic properties of these complexes can be attributed to the variations in the quantity of d-orbital electrons,thereby influencing their spin and orbital characteristics.The d-orbitals facilitate the formation of stable multidirectional bonds with ligands,resulting in a variety of geometric structures and rich coordination chemistry.These interactions result in variations in energy levels,thereby producing diverse electrical properties,including low attenuation coefficients,high rectification ratios,and unique multichannel transmission.Moreover,the unpaired electrons inthe d-orbitals can give rise to diverse magnetic behaviors,leading to magnetic effects such as spin-related interfaces,switches,and magnetoresistance.This paves the way for extensive possibilities in the design and application of single-molecule devices.This review elaborates on singlemolecule physical properties of transition metal complexes,including length attenuation,rectification,multi-channel transmission,thermoelectric effect,and spin regulation,which are vital for the functionalization and regulation of molecular electronics.In addition,this review also explores the correlation between these physical properties and the electronic structure of transition metals,discussing the broad prospects of transition metal complexes in the fields of nanoelectronics,optoelectronics,and quantum technology.
基金primary financial supports from the National Key R&D Program of China(2021YFA1200102,2021YFA1200101,and 2022YFE0128700)the National Natural Science Foundation of China(22173050,22150013,21727806,and 21933001)+4 种基金the New Cornerstone Science Foundation through the XPLORER PRIZEthe Natural Science Foundation of Beijing(2222009)Beijing National Laboratory for Molecular Sciences(BNLMS202105)the Fundamental Research Funds for the Central Universities(63223056)“Frontiers Science Center for New Organic Matter”at Nankai University(63181206).
文摘Single-molecule junctions,integrating individual molecules as active components between electrodes,serve as fundamental building blocks for advanced electronic and sensing technologies.The application of ionic liquids in single-molecule junctions represents a cutting-edge and rapidly evolving field of research at the intersection of nanoscience,materials chemistry,and electronics.This review explores recent advances where ionic liquids function as electrolytes,dielectric layers,and structural elements within single-molecule junctions,reshaping charge transport,redox reactions,and molecular behaviors in these nanoscale systems.We comprehensively dissect fundamental concepts,techniques,and modulation mechanisms,elucidating the roles of ionic liquids as gates,electrochemical controllers,and interface components in singlemolecule junctions.Encompassing applications from functional device construction to unraveling intricate chemical reactions,this review maps the diverse applications of ionic liquids in single-molecule junctions.Moreover,we propose critical future research topics in this field,including catalysis involving ionic liquids at the single-molecule level,functionalizing single-molecule devices using ionic liquids,and probing the structure and interactions of ionic liquids.These endeavors aim to drive technological breakthroughs in nanotechnology,energy,and quantum research.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11974217,12204281,and 21933002)the Shandong Provincial Natural Science Foundation (Grant No.ZR2022QA068)。
文摘Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions.Here,using the first-principles method,we theoretically investigate spin transport properties and photoresponse characteristics in trimesic acid magnetic single-molecule junctions with different molecular adsorption orientations and electrode contact sites.The transport calculations indicate that a single-molecule switch and a significant enhancement of spin transport and photoresponse can be achieved when the molecular adsorption orientation changes from planar geometry to upright geometry.The maximum spin polarization of current and photocurrent in upright molecular junctions exceeds 90%.Moreover,as the Ni tip electrode moves,the tunneling magnetoresistance of upright molecular junctions can be increased to 70%.The analysis of the spin-dependent PDOS elucidates that the spinterfaces between organic molecule and ferromagnetic electrodes are modulated by molecular adsorption orientation,where the molecule in upright molecular junctions yields higher spin polarization.Our theoretical work paves the way for designing spintronic devices and optoelectronic devices with anisotropic functionality base on anisotropic molecules.
基金supported by Guangxi Science and Technology Program(No.GuiKeAD23026291)Guangxi Science and Technology Major Project(No.AA22068057).
文摘Clustering is a pivotal data analysis method for deciphering the charge transport properties of single molecules in break junction experiments.However,given the high dimensionality and variability of the data,feature extraction remains a bottleneck in the development of efficient clustering methods.In this regard,extensive research over the past two decades has focused on feature engineering and dimensionality reduction in break junction conductance.However,extracting highly relevant features without expert knowledge remains an unresolved challenge.To address this issue,we propose a deep clustering method driven by task-oriented representation learning(CTRL)in which the clustering module serves as a guide for the representation learning(RepL)module.First,we determine an optimal autoencoder(AE)structure through a neural architecture search(NAS)to ensure efficient RepL;second,the RepL process is guided by a joint training strategy that combines AE reconstruction loss with the clustering objective.The results demonstrate that CTRL achieves excellent performance on both the generated and experimental data.Further inspection of the RepL step reveals that joint training robustly learns more compact features than the unconstrained AE or traditional dimensionality reduction methods,significantly reducing misclustering possibilities.Our method provides a general end-to-end automatic clustering solution for analyzing single-molecule break junction data.
基金supported by the National Key R&D Program of China(Nos.2022YFB3204402,2020YFA0714703 and 2022YFC2205003)the National Natural Science Foundation of China(No.22204135)+2 种基金Hunan Provincial Natural Science Foundation of China(No.2023JJ40619)the Education Department of Hunan Province(No.23A0114)the Science and Technology Innovation Program of Hunan Province(No.2022RC3027)。
文摘Gaining insights into charge transport related to conformational changes and ion transport in valinomycin(VM)is crucial for understanding the underlying physiological processes and advancing ion carrier applications.Observing these processes in single molecules provides deeper insights and precision than those obtained through conventional ensemble measurements.Herein,we employed a single-molecule conductance measurement method based on the scanning tunneling microscopy break-junction(STM-BJ)to measure the charge transport of individual VM molecules in both non-polar and polar solvents,as well as when mediated by K^(+)ions.Single-molecule conductance measurements revealed that the bracelet and propeller-type conformations of VM in both non-polar and polar solvents significantly affect its conductance.In polar solvents,the propeller-type conformation of VM demonstrated a well-defined conductance signature,single-molecule rectification feature,and through-space transmission mechanism.Specifically,the introduction of K^(+)ions in polar solvents induced a conformational transition from the propeller-type to the bracelet-type form,facilitating K^(+)binding recognition.These observations were further supported by density functional theory combined with non-equilibrium Green’s function calculations.This study enhanced the fundamental understanding of the electronic transport mechanisms in VM and valinomycin-K^(+)molecular junctions,offering insights into VM ionophores and promoting supramolecular sensing applications.
文摘π-πstacking,a fundamental noncovalent interaction between aromatic molecules,is essential for enabling charge transport across molecular fragments a process vital to both chemistry and biology.^(1,2)Owing to the widespread importance ofπ-πinteractions in diverse fields,there is considerable interest in precisely modulating the interaction at the single-molecule scale.Studies have shown thatπ-πinteraction can be influenced by adjusting molecular concentration,^(3) applying mechanical forces,^(4) or designing target molecules with enhanced attraction.^(5)However,achieving precise control of intermolecularπ-πinteraction at the single-molecule level without altering molecular conformation or concentration remains a significant challenge.
基金National Key R&D Program of China,Grant/Award Number:2017YFA0204901National Natural Science Foundation of China,Grant/Award Numbers:21727806,21933001Natural Science Foundation of Beijing,Grant/Award Number:Z181100004418003。
文摘Single-molecule electrical and spin switches have been one of the main research focuses in molecular electronics and spintronics because they may form the most important elements for the future information technology,thus attracting great attention in the scientific community and witnessing significant progresses benefiting from the combination of physics,chemistry,materials,and engineering.The key issue of constructing single-molecule switches is the development of stimulus-responsive systems that provide bistable or multiple states.In this review,we summarize the recent advances of this field in terms of the external stimulus that induces the switching.A variety of external stimuli,such as light,electric field,magnetic field,mechanical force,and chemical stimulus,have been successfully employed to activate the reversible switching in single-molecule junctions by manipulating molecular structures,conformations,electronic states,and spin states.As a burgeoning field,we finally put forward the challenges in molecular electronics and spintronics that need to be solved,which will initiate intense research.
基金supported by the National Natural ScienceFoundation of China (Nos. 22173075, 21933012 and 31871877)the National Key R&D Program of China (No. 2017YFA0204902)+1 种基金the Fundamental Research Funds for the Central Universities(Nos. 20720200068 and 20720190002)the Beijing NationalLaboratory for Molecular Sciences (No. BNLMS202005).
文摘The investigation of electronic excited states in single-molecule junctions not only provides platforms to reveal the photophysical and photochemical processes at the molecular level,but also brings opportunities for the development of single-molecule optoelectronic devices.Understanding the interaction mechanisms between molecules and nanocavities is essential to obtain ondemand properties in devices by artificial design,since molecules in junctions exhibit unique behaviors of excited states benefited from the structures of metallic nanocavities.Here,we review the excitation mechanisms involved in the interplay between molecules and plasmonic nanocavities,and reveal the influence of nanostructures on excited-state properties by demonstrating the differences in excited state decay processes.Furthermore,vibronic transitions of molecules between nanoelectrodes are also discussed,offering a new single-molecule characterization method.Finally,we provide the potential applications and challenges in single-molecule optoelectronic devices and the possible directions in exploring the underlying mechanisms of photophysical and photochemical processes.
基金supported by Natural Science Foundation of China(nos.21722305,21673195,21703188,51733004,and 51525303)the National Key R&D Program of China(nos.2017YFA0204902 and 2017YFA0204903)+1 种基金the Beijing National Laboratory for Molecular Sciences(no.BNLMS202005)the China Postdoctoral Science Foundation(no.2017M622060).
文摘Electronic coupling between individual building blocks plays an essential role in charge transport through molecular materials and devices.However,the investigation of the transmission mechanism in charge transport via intramolecular coupling remains challenging.Herein,we demonstrate the transition of the intramolecular through-bond and through-space coupling in a single-molecule junction with a family of diketopyrrolopyrrole(DPP)derivative by varying intramolecular donor–acceptor(D–A)interactions.The transition is accomplished by regulating D–A interactions by inserting different aromatic rings inside,leading to two orders of magnitude difference of the single-molecule conductance.The flicker noise analysis demonstrates that the conductance difference arises from the control of the contribution between through-bond and through-space coupling.These findings are further supported by the calculation that the intramolecular coupling among molecular building blocks correlates with the D–A interaction,providing a promising way to regulate the contribution between through-bond and through-space coupling in the charge transport through molecular materials and devices.
基金financially supported by the Program of Higher-Level Talents of IMU(No.21300-5223748)the National Natural Science Foundation of China(Nos.22103065 and 21661024)
文摘The electronic structure of semiconductor materials governs the law of electron motion,which profoundly affects the properties such as conductivity and photoelectric conversion.Photo-responsive single-molecule junction technology provides insights into the electronic structure of photogenerated substances at the molecular scale,enabling the characterization of dynamic processes such as charge separation and energy transfer.These processes involve the unique quantum state known as the "exciton".The electrical characterization technique based on single molecule break junction facilities direct measurement of the photoelectric response of molecules at nanometer and subnanometer scale.This study reviews recent research progress of exciton effects and the characterization of optoelectronic phenomena.The mechanisms of exciton effects in three key optoelectronic phenomena—photoconductivity,photovoltaic s,and photoluminescence—are discussed.Furthermore,advanced spectral characterization techniques applied to the in-situ monitoring of single-molecule optoelectronic devices are highlighted.These include Raman spectroscopy with various enhancements,inelastic electron tunneling spectroscopy,and ultrafast spectroscopy with high resolution.
基金supported by the National Natural Science Foundation of China(Nos.21722305,21933012,31871877)the National Key R&D Program of China(No.2017YFA0204902)+4 种基金the Fundamental Research Funds for the Central Universities(Nos.20720200068,20720190002)the Natural Science Foundation of Shanghai(No.20ZR1471600)the Science and Technology Commission of Shanghai Municipality(No.19DZ2271100)Natural Science Foundation of Fujian Province(No.2018J06004)the Beijing National Laboratory for Molecular Sciences(No.BNLMS202005)。
文摘Quantum interference(QI)effects,which offer unique opportunities to widely manipulate the charge transport properties in the molecular junctions,will have the potential for achieving high thermopower.Here we developed a scanning tunneling microscope break junction technique to investigate the thermopower through single-molecule thiophene junctions.We observed that the thermopower of 2,4-TPSAc with destructive quantum interference(DQI)was nearly twice of 2,5-TP-SAc without DQI,while the conductance of the 2,4-TP-SAc was two orders of magnitude lower than that of 2,5-TP-SAc.Furthermore,we found the thermopower was almost the same by altering the anchoring group or thiophene core in the control experiments,suggesting that the QI effect is responsible for the increase of thermopower.The density functional theory(DFT)calculations are in quantitative agreement with the experimental data.Our results reveal that QI effects can provide a promising platform to enhance the thermopower of molecular junctions.
基金supported by the National Nature Science Foundation of China(22173085 and 21803061)China Postdoctoral Science Foundation(2022M722597)the Fundamental Research Funds for the Central Universities(No.2652019030).
文摘Hydrogen bonding is a vital driving force for organizing the hierarchy of molecular structure,especially in biologic field.Due to its directionality,selectivity and moderate strength,hydrogen bonding has been extensively introduced into the molecular recognition,sensing and electronic devices.Electric measurements at single-molecule level facilitate the investigation of hydrogen bonds and provide a comprehensive understanding of the electron transport properties governed by the hydrogen bonding,which is essential for the development of self-assembled electronic systems.This review provides a detailed overview of recent advancements in constructing single-molecule junctions utilizing intramolecular and intermolecular hydrogen bonding.We first introduce the methods utilized for characterizing the electric and dynamic properties of non-covalent interactions.Next,we discuss the mechanisms of electron transport,relevant influencing factors,and typical applications utilizing electrical signals based on single-molecule junctions.Finally,we propose our perspective on the existing challenges and prospective opportunities in utilizing hydrogen bonding for electronic device applications.
基金supported by the National Natural Science Foundation of China(22105172)the Natural Science Foundation of Zhejiang Province(LQ22B040003)the Fundamental Research Funds of Zhejiang Sci-Tech University(21062113-Y).
文摘Investigating the quantum interference effect in single molecules is essential to comprehensively understand the underlying mechanism of single-molecule charge transport.In this study,we employed the mother molecule m-OPE and introduced a series of side groups with various electronic effects at the 2-position of the central phenyl ring,creating four daughter m-OPE derivatives.The single molecular conductivities of these molecule wires were measured using the scanning tunneling microscope breaking junction technique.Our findings demonstrate that the substitutions regularly modulate the destructive quantum interference occurring within the m-OPE molecules.By combining optical and electrochemical investigations,along with density functional theory computations,we discover that the conductivity of the molecules corresponds to the electron-donating/withdrawing ability of the substituents.Specifically,by adjusting the electron structures of the molecular backbone,we can systematically tailor the destructive quantum interference in the m-OPE molecules.
基金This work was supported by the National Natural Science Foundation of China(grant nos.21875279,21790362,and 22075080)the Shanghai Municipal Science and Technology Major Project(grant no.2018SHZDZX03)+1 种基金the Fundamental Research Funds for the Central Universities,the Programme of Introducing Talents of Discipline to Universities(grant no.B16017)the Program of Shanghai Academic/Technology Research Leader(grant no.19XD1421100).
文摘To monitor and investigate chemical reactions in real time and in situ is a long-standing,challenging goal in chemistry.Herein,an electric potential-promoted oxidative coupling reaction of organoboron compounds without the addition of base is reported,and the transmetallation process involved is monitored in real time and in situ with the scanning tunneling microscopy break single-molecule junctions(STMBJ)technique.We found that the electric potential applied determined the transmetallation.At low-bias voltage,the first-step transmetallation process occurred and afforded Au─C-bonded aryl gold intermediates.The electronic properties of organoboron compounds have a strong influence on the transmetallation process,and electron-rich compounds facilitate this transformation.At high-bias voltage,the second-step transmetallation process took place,and the corresponding intermediate(highly reactive diaryl metal complex)was detected with the assistance of Pd(OAc)_(2).Our work demonstrates the applications of STMBJ on in situ monitoring and catalyzing of chemical reactions and provides a new methodology to fabricate singlemolecule devices.
基金financial support from Science and Technology Project of Guangdong(2020B010190001)National Natural Science Foundation(12434016).
文摘Raman spectroscopy offers a great power to detect,analyze and identify molecules,and monitor their temporal dynamics and evolution when combined with single-molecule surface-enhanced Raman scattering(SM-SERS)substrates.Here we present a SM-SERS scheme that involves simultaneously giant chemical enhancement from WS22D materials,giant electromagnetic enhancement from plasmonic nanogap hot spot,and inhibition of molecular fluorescence influence under near-infrared laser illumination.Remarkably we find Coulomb attraction between analyte and gold nanoparticle can trigger spontaneous formation of molecule-hotspot pairing with high precision,stability and robustness.The scheme has enabled realization of universal,robust,fast,and large-scale uniform SM-SERS detection for three Raman molecules of rhodamine B,rhodamine 6G,and crystal violet with a very low detection limit of 10−16 M and at a very fast spectrum acquisition time of 50 ms.
基金supported by the Ministry of Science and Technology of China(No. SQ2017YFJC020081)the National Natural Science Foundation of China(Nos. 21673195,21503179)+2 种基金Fundamental Research Funds for the Central Universities in China (Xiamen University: No. 20720170035)Natural Science Foundation of Fujian Province(No. 2016J05162)the Young Thousand Talent Project of China
文摘The quantum interference effect in the charge transport through single-phenyl molecules received intensive interests from theory but remained as an experimental challenge. In this paper, we investigated the charge transport through single-molecule benzene dithiol （BDT） junction with different connectivities using mechanically controllable break.junction （MCB]） technique. By further improving the mechanical stability and the electronic measuring component of the MCBJ set-up, we obtained the conductance histograms of BDT molecules （BDTs） from the statistical analysis of conductance-distance traces without data selection. By tuning the connectivity, the conductance of BDTs is determined to be 10-12Go, 10-22Go and 10-10Go for pcra, meta, and ortho connectivity, following the trend that ortfio-BDT 〉 para-BDT 〉 meta-BDT. Furthermore, the displacements of the junctions followed the trend that para 〉 meta 〉 ortho, suggesting the charge transport through the molecules via the gold-thiol bond. The different trends between conductance and displacement for different connectivities suggests the presence of destructive quantum interference effect on meta-BDT, which provides the experimental evidence for the quantum interference effect through single-phenyl molecular junctions.
基金financially supported by the National Natural Science Foundation of China(Nos.U23A20594,22375066 and 21788102)Guang Dong Basic and Applied Basic Research Foundation(No.2023B1515040003)。
文摘Quinoid structures are considered to be conducive to the charge transport of organic molecules,but this hypothesis is rarely proven at single-molecule level.Herein,as a proof of concept,the single-molecule conductance of two furan-based isomers,3,3'-bis(4-(methylthio)phenyl)-2,2'-bifuran(2,2'-SMPBF)and 4,4'-bis(4-(methylthio)phenyl)-3,3'-bifuran(3,3'-SMPBF),is investigated by the scanning tunneling microscopy break junction(STM-BJ)technique and theoretical simulation.2,2'-SMPBF prefers to adopt a nearly planar conformation with intact alternating single and double bonds extended via2,2'-bifuran moiety and therefore exhibits goodπ-conjugation and a prominent quinoid structure.However,theπ-conjugation of 3,3'-SMPBF is interrupted due to ineffective cross-conjugation in the 3,3'-bifuran moiety,leading to the absence of a quinoid structure.2,2'-SMPBF displays switchable multiple conductances induced by the interconversion between folded and unfolded conformations and an abnormal rebound of conductance along with the increases of electrode displacement,which is demonstrated to be caused by the quinoid structure in a nearly planar conformation during the stretching process.However,3,3'-SMPBF without a quinoid structure in unfolded conformation exhibits extremely low conductance that cannot be captured in STM-BJ measurements.These results reveal the significant contribution of quinoid structure to molecular charge transport and provide valuable information on the structure-transport relationship for the design of efficient organic semiconductors.
基金supported by the Fundamental Research Funds for the Central Universities in China (Xiamen University: 20720170035)the National Natural Science Foundation of China (21503179, 61573295, 21722305)the Nation Key R&D Program of China (2017YFA0204902)
文摘State-of-the-art molecular electronics focus on the measurement of electrical properties of materials at the single-molecule level.Experimentally, molecular electronics face two primary challenges. One challenge is the reliable construction of single-molecule junctions, and the second challenge is the arbitrary modulation of electron transport through these junctions. Over the past decades, electrochemistry has been widely adopted to meet these challenges, leading to a wealth of novel findings. This review starts from the application of electrochemical methods to the fabrication of nanogaps, which is an essential platform for the construction of single-molecule junctions. The utilization of electrochemistry for the modification of molecular junctions,including terminal groups and structural backbones, is introduced, and finally, recent progress in the electrochemical modulation of single-molecule electron transport is reviewed.
基金This work was supported by National Key R&D Project of China(2017YFA0204902)National Natural Science Foundation of China(21722305,21673195,21973079)+2 种基金FET Open project 767187–Qu IETthe EU project BAC-TO-FUELthe UK EPSRC grants EP/N017188/1,EP/P027156/1 and EP/N03337X/1
文摘To explore solvent gating of single-molecule electrical conductance due to solvent-molecule interactions, charge transport through single-molecule junctions with different anchoring groups in various solvent environments was measured by using the mechanically controllable break junction technique. We found that the conductance of single-molecule junctions can be tuned by nearly an order of magnitude by varying the polarity of solvent. Furthermore, gating efficiency due to solvent–molecule interactions was found to be dependent on the choice of the anchor group. Theoretical calculations revealed that the polar solvent shifted the molecular-orbital energies, based on the coupling strength of the anchor groups. For weakly coupled molecular junctions, the polar solvent–molecule interaction was observed to reduce the energy gap between the molecular orbital and the Fermi level of the electrode and shifted the molecular orbitals. This resulted in a more significant gating effect than that of the strongly coupled molecules. This study suggested that solvent–molecule interaction can significantly affect the charge transport through single-molecule junctions.
