Controlling single molecule conductance by a locally induced chemical reaction on individual thiophene units

The authors acknowledge the Emmy-Noether-Program of the Deutsche Forschungsgemeinschaft, the SFB 767, Core Program PN19-03 (contract number 21 N/08.02.2019) founded by the Romanian Ministry of Research and Innovation, Basque Departamento de Universidades e Investigación (grant no. IT-756-13), the Spanish Ministerio de Economía y Competitividad (grant no. FIS2013-48286-C2-8752-P and FIS2016-75862-P) andthe Operational Programme Research, Development and Education financed by European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16_019/0000760).Among the prerequisites for the progress of single‐molecule‐based electronic devices are a better understanding of the electronic properties at the individual molecular level and the development of methods to tune the charge transport through molecular junctions. Scanning tunneling microscopy (STM) is an ideal tool not only for the characterization, but also for the manipulation of single atoms and molecules on surfaces. The conductance through a single molecule can be measured by contacting the molecule with atomic precision and forming a molecular bridge between the metallic STM tip electrode and the metallic surface electrode. The parameters affecting the conductance are mainly related to their electronic structure and to the coupling to the metallic electrodes. Here, the experimental and theoretical analyses are focused on single tetracenothiophene molecules and demonstrate that an in situ‐induced direct desulfurization reaction of the thiophene moiety strongly improves the molecular anchoring by forming covalent bonds between molecular carbon and copper surface atoms. This bond formation leads to an increase of the conductance by about 50 % compared to the initial state.Publisher PDFPeer reviewe

Significance of nuclear quantum effects in hydrogen bonded molecular chains

In hydrogen bonded systems, nuclear quantum effects such as zero-point motion and tunneling can significantly affect their material properties through underlying physical and chemical processes. Presently, direct observation of the influence of nuclear quantum effects on the strength of hydrogen bonds with resulting structural and electronic implications remains elusive, leaving opportunities for deeper understanding to harness their fascinating properties. We studied hydrogen-bonded one-dimensional quinonediimine molecular networks which may adopt two isomeric electronic configurations via proton transfer. Herein, we demonstrate that concerted proton transfer promotes a delocalization of {\pi}-electrons along the molecular chain, which enhances the cohesive energy between molecular units, increasing the mechanical stability of the chain and giving rise to new electronic in-gap states localized at the ends. These findings demonstrate the identification of a new class of isomeric hydrogen bonded molecular systems where nuclear quantum effects play a dominant role in establishing their chemical and physical properties. We anticipate that this work will open new research directions towards the control of mechanical and electronic properties of low-dimensional molecular materials via concerted proton tunneling

On-surface synthesis of a dicationic diazahexabenzocoronene derivative on the Au(111) surface

The atomically precise control over the size, shape and structure of nanographenes (NGs) or the introduction of heteroatom dopants into their sp2-carbon lattice confer them valuable electronic, optical and magnetic properties. Herein, we report on the design and synthesis of a hexabenzocoronene derivative embedded with graphitic nitrogen in its honeycomb lattice, achieved via on-surface assisted cyclodehydrogenation on the Au(111) surface. Combined scanning tunnelling microscopy/spectroscopy and non-contact atomic force microscopy investigations unveil the chemical and electronic structures of the obtained dicationic NG. Kelvin probe force microscopy measurements reveal a considerable variation of the local contact potential difference toward lower values with respect to the gold surface, indicative of its positive net charge. Altogether, we introduce the concept of cationic nitrogen doping of NGs on surfaces, opening new avenues for the design of novel carbon nanostructure

Generating antiaromaticity in polycyclic conjugated hydrocarbons by thermally selective skeletal rearrangements at interfaces

Antiaromatic polycyclic conjugated hydrocarbons (PCHs) are attractive research targets because of their interesting structural, electronic and magnetic properties. Unlike aromatic compounds, the synthesis of antiaromatic PCHs is challenging because of their high reactivity and lack of stability, which stems from the small energy gap between their highest occupied and lowest unoccupied molecular orbitals. Here we describe a strategy for the introduction of antiaromatic units in PCHs via thermally selective intra- and intermolecular ring-rearrangement reactions of dibromomethylene-functionalized molecular precursors upon sublimation on a hot Au(111) metal surface, not available in solution chemistry. The synthetic value of these reactions is proven by the integration of pentalene segments into acene-based precursors, which undergo intramolecular ring rearrangement, and the formation of π-conjugated ladder polymers, linked through cyclobutadiene connections, due to ring-rearrangement and homocoupling reactions of indenofluorene-based precursors. The reaction products are investigated by scanning tunnelling microscopy and non-contact atomic force microscopy, and mechanistic insights are unveiled by computational studies. [Figure not available: see fulltext.] © 2023, The Author(s), under exclusive licence to Springer Nature Limited.This project has received funding from Comunidad de Madrid (projects QUIMTRONIC-CM (Y2018/NMT-4783) and NanoMagCost (P2018/NMT-4321)), an ERC Consolidator Grant (ELECNANO, 766555), ERC (SyG TOMATTO ERC-2020-951224) and Ministerio de Ciencia, Innovacion y Universidades (projects SpOrQuMat (PGC2018-098613-B-C21), CTQ2017-83531-R, PID2019-108532GB-I00, PID2020-114653RB-I00 and CTQ2016-81911-REDT). We acknowledge the support from the ‘(MAD2D-CM)-UCM’ and the ‘(MAD2D-CM)-IMDEA-Nanociencia’ projects funded by Comunidad de Madrid, by the Recovery, Transformation and Resilience Plan, and by NextGenerationEU from the European Union. IMDEA Nanociencia is appreciative of support from the ‘Severo Ochoa’ Programme for Centers of Excellence in R&D (MINECO, grant nos. SEV-2016-0686 and CEX2020-001039-S). Q.C., D.S.-P. and P.J. acknowledge funding support from the CzechNanoLab Research Infrastructure supported by MEYS CR (LM2023051) and GACR project no. 20-13692X. Computational resources were provided by the e-INFRA CZ project (ID 90140), supported by the Ministry of Education, Youth and Sports of the Czech Republic. A.S.-G. acknowledges funding from the ‘Ministerio de Universidades’ for the ‘Plan de Recuperación, Transformación y Resiliencia’ under Margarita Salas grant agreement CA1/RSUE/2021-00369. J.I.U. acknowledges the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 886314. We acknowledge B. Cirera for fruitful discussions.The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. The Fireball software package is available 458 at: https://github.com/fireball-QMD and PP-SPM software package can be downloaded at: https://github.com/Probe-Particle/ppafm#probe-particle-model.Peer reviewe

Interface Dipoles of Ir(ppy)₃ on Cu(111)

The interplay of adsorption geometry and interface dipoles of the transition-metal complex \molecule\ on Cu(111) was studied using low-temperature scanning probe microscopy and density-functional-theory calculations. We find that the orientation of the molecule's intrinsic dipole moment with respect to the surface has a strong influence to the total energy of the different configurations, where the most stable one has the molecular dipole moment pointing out of the surface plane along the surface normal. Adsorption-induced redistribution of charges results in an additional dipole moment that also points out of the surface plane for all configurations. Submolecularly resolved maps of the resulting local contact potential difference suggest that any in-plane dipole moment is very effectively screened