22 research outputs found
On-surface synthesis of doubly-linked one-dimensional pentacene ladder polymers
No full textOn-surface investigations of pentacene molecules functionalized with four dibromomethylene groups reveal, after an annealing step, the formation of π-conjugated ladder polymers doubly-linked by ethynylene bridges on a Au(111) surface.Comunidad de MadrdidEuropean CommissionMInisterio de Economía y Competitividad (España)Depto. de Química OrgánicaFac. de Ciencias QuímicasTRUEpu
Atomic Scale Control and Visualization of Topological Quantum Phase Transition in π‐Conjugated Polymers Driven by Their Length
No full textAbstract: Quantum phase transitions (QPTs) driven by quantum fluctuations are transitions between distinct quantum phases of matter. At present, they are poorly understood and not readily controlled. Here, scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc‐AFM) are used to explore atomic scale control over quantum phase transitions between two different topological quantum states of a well‐defined π‐conjugated polymer. The phase transition is driven by a pseudo Jahn–Teller effect that is activated above a certain polymer chain length. In addition, theoretical calculations indicate the presence of long‐lasting coherent fluctuations between the polymer's two quantum phases near the phase transition, at finite temperature. This work thus presents a new way of exploring atomic‐scale control over QPTs and indicates that emerging quantum criticality in the vicinity of a QPT can give rise to new states of organic matter.Depto. de Química OrgánicaFac. de Ciencias QuímicasTRUEpu
Atomically precise control of topological state hybridization in conjugated polymers
No full textRealization of topological quantum states in carbon nanostructures has recently emerged as a promising platform for hosting highly coherent and controllable quantum dot spin qubits. However, their adjustable manipulation remains elusive. Here, we report the atomically accurate control of the hybridization level of topologically protected quantum edge states emerging from topological interfaces in bottom-up-fabricated π-conjugated polymers. Our investigation employed a combination of low-temperature scanning tunneling microscopy and spectroscopy, along with high-resolution atomic force microscopy, to effectively modify the hybridization level of neighboring edge states by the selective dehydrogenation reaction of molecular units in a pentacene-based polymer and demonstrate their reversible character. Density functional theory, tight binding, and complete active space calculations for the Hubbard model were employed to support our findings, revealing that the extent of orbital overlap between the topological edge states can be finely tuned based on the geometry and electronic bandgap of the interconnecting region. These results demonstrate the utility of topological edge states as components for designing complex quantum arrangements for advanced electronic devices.We acknowledge the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic under Project No. LM2023066. B.T. acknowledges the financial support of Czech Science Foundation (project-23-06781M) and from MCIN/AEI/10.13039/501100011033/ERDF/EU (project-PID2022-140845OB-C64). We appreciate funding from the CzechNanoLab Research Infrastructure supported by MEYS CR (LM2018110) and project GACR no. 23-05486S. We acknowledge the support from the ‘(MAD2D-CM)-IMDEA-Nanociencia’ project funded by Comunidad de Madrid, by the Recovery, Transformation and Resilience Plan, and by NextGenerationEU from the European Union. N.M. acknowledges MICIN of Spain for funding the project PID2020-114653RB-I00. H.G.-H. acknowledges financial support from the Spanish State Research Agency under grant Ramon y Cajal fellowship RYC2021-031050-I.Peer reviewe
Unravelling the Open-Shell Character of Peripentacene on Au(111)
No full textPolycyclic aromatic hydrocarbons (PAHs) are a family of organic compounds comprising two or more fused aromatic rings which feature manifold applications in modern technology. Among these species, those presenting an open-shell magnetic ground state are of particular interest for organic electronic, spintronic, and non-linear optics and energy storage devices. Within PAHs, special attention has been devoted in recent years to the synthesis and study of the acene and fused acene (periacene) families, steered by their decreasing HOMO–LUMO gap with length and predicted open-shell character above some size. However, an experimental fingerprint of such magnetic ground state has remained elusive. Here, we report on the in-depth electronic characterization of isolated peripentacene molecules on a Au(111) surface. Scanning tunnelling spectroscopy, complemented by computational investigations, reveals an antiferromagnetic singlet ground state, characterized by singlet–triplet inelastic excitations with an experimental effective exchange coupling (Jeff) of 40.5 meV. Our results deepen the fundamental understanding of organic compounds with magnetic ground states, featuring perspectives in carbon-based spintronic devices.Depto. de Química OrgánicaFac. de Ciencias QuímicasTRUEpu
Circumventing the Stability Problems of Graphene Nanoribbon Zigzag Edges
No full textCarbon nanostructures with zigzag edges exhibit unique properties with
exciting potential applications. Such nanostructures are generally synthesized
under vacuum because their zigzag edges are unstable under ambient conditions:
a barrier that must be surmounted to achieve their scalable exploitation. Here,
we prove the viability of chemical protection/deprotection strategies for this
aim, demonstrated on labile chiral graphene nanoribbons (chGNRs). Upon
hydrogenation, the chGNRs survive an exposure to air, after which they are
easily converted back to their original structure via annealing. We also
approach the problem from another angle by synthesizing a chemically stable
oxidized form of the chGNRs that can be converted to the pristine hydrocarbon
form via hydrogenation and annealing. These findings may represent an important
step toward the integration of zigzag-edged nanostructures in devices
Chemical stability of (3,1)-chiral graphene nanoribbons
No full textNanostructured graphene has been widely studied in recent years due to the tunability of its electronic properties and its associated interest for a variety of fields, such as nanoelectronics and spintronics. However, many of the graphene nanostructures of technological interest are synthesized under ultrahigh vacuum, and their limited stability as they are brought out of such an inert environment may compromise their applicability. In this study, a combination of bond-resolving scanning probe microscopy (BR-SPM), along with theoretical calculations, has been employed to study (3,1)-chiral graphene nanoribbons [(3,1)-chGNRs] that were synthesized on a Au(111) surface and then exposed to oxidizing environments. Exposure to the ambient atmosphere, along with the required annealing treatment to desorb a sufficiently large fraction of contaminants to allow for its postexposure analysis by BR-SPM, revealed a significant oxidation of the ribbons, with a dramatically disruptive effect on their electronic properties. More controlled experiments avoiding high temperatures and exposing the ribbons only to low pressures of pure oxygen show that also under these more gentle conditions the ribbons are oxidized. From these results, we obtain additional insights into the preferential reaction sites and the nature of the main defects that are caused by oxygen. We conclude that graphene nanoribbons with zigzag edge segments require forms of protection before they can be used in or transferred through ambient conditions.We acknowledge funding from the European Union’s Horizon 2020 program (Grant Agreement No. 635919), from the Spanish Agencia Estatal de Investigación (Grant Nos. PID2019-107338RB-C62 and PID2019-107338RB-C63), Gobierno Vasco (PIBA_2020_1_0036), Consejo Superior de Investigaciones Científicas (CSIC, LINKC20002), Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019–2022, ED431G 2019/03), from the European Regional Development Fund-ERDF, from Praemium Academie of the Academy of Science of the Czech Republic (GACR project no. 20-13692X), and CzechNanoLab Research Infrastructure supported by MEYS CR (LM2018110).Peer reviewe
Real-Space Imaging of the Conformation and Atomic Structure of Individual β Cyclodextrins with Noncontact AFM
No full textGlycans, consisting of covalently linked sugar units, are a major class of biopolymers essential to all known living organisms. To better understand their biological functions and further applications in fields from biomedicine to materials science, detailed knowledge of their structure is essential. However, due to the extraordinary complexity and conformational flexibility of glycans, state-of-the-art glycan analysis methods often fail to provide structural information with atomic precision. Here, we combine electrospray deposition in ultra-high vacuum with noncontact atomic force microscopy and theoretical calculations to unravel the structure of β-cyclodextrin, a cyclic glucose oligomer, with atomic-scale detail. Our results, established on the single-molecule level, reveal the different adsorption geometries and conformations of β-cyclodextrin. The cyclic arrangement of hydroxy groups on both faces of the molecule and the stabilizing H-bonds are imaged with atomic resolution, enabling the unambiguous assignment of the molecular structure and demonstrating the potential of the method for glycan analysis
Atomically precise control of topological state hybridization in conjugated polymers
No full textResumen del trabajo presentado al DPG Spring Meeting of the Condensed Matter Section (SKM), celebrado en la Universidad de Regensburg (Alemania) del 16 al 21 de marzo de 2025.Realization of topological quantum states in carbon nanostructures has recently emerged as a promising platform for hosting highly coherent and controllable quantum dot spin qubits. However, their adjustable manipulation remains elusive. Here, we report the atomically accurate control of the hybridization level
of topologically protected quantum edge states emerging from topological interfaces in bottom-up-fabricated π-conjugated polymers. Our investigation employed a combination of low-temperature scanning tunneling microscopy and spectroscopy, along with high-resolution atomic force microscopy, to effectively modify the hybridization level of neighboring edge states by the selective dehydrogenation reaction of molecular units in a pentacene-based polymer and demonstrate their reversible character.Peer reviewe
Diradical Organic One‐Dimensional Polymers Synthesized on a Metallic Surface
No full textAbstract
We report on the synthesis and characterization of atomically precise one‐dimensional diradical peripentacene polymers on a Au(111) surface. By means of high‐resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet–triplet spin‐flip inelastic excitations with an effective exchange coupling (J eff) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon‐based optoelectronics and spintronics.European CommissionComunidad de MadridMinisterio de Economía y Competitividad (España)Depto. de Química OrgánicaFac. de Ciencias QuímicasTRUEpu
Atomically resolved imaging of the conformations and adsorption geometries of individual β-cyclodextrins with non-contact AFM
No full textGlycans, consisting of covalently linked sugar units, are a major class of biopolymers essential to all known living organisms. To better understand their biological functions and further applications in fields from biomedicine to materials science, detailed knowledge of their structure is essential. However, due to the extraordinary complexity and conformational flexibility of glycans, state-of-the-art glycan analysis methods often fail to provide structural information with atomic precision. Here, we combine electrospray deposition in ultra-high vacuum with non-contact atomic force microscopy and theoretical calculations to unravel the structure of β-cyclodextrin, a cyclic glucose oligomer, with atomic-scale detail. Our results, established on the single-molecule level, reveal the different adsorption geometries and conformations of β-cyclodextrin. The position of individual hydroxy groups and the location of the stabilizing intramolecular H-bonds are deduced from atomically resolved images, enabling the unambiguous assignment of the molecular structure and demonstrating the potential of the method for glycan analysis
