Transferring Axial Molecular Chirality Through a Sequence of On-Surface Reactions

Fine management of chiral processes on solid surfaces has progressed over the years, yet still faces the need for the controlled and selective production of advanced chiral materials. Here, we report on the use of enantiomerically enriched molecular building blocks to demonstrate the transmission of their intrinsic chirality along a sequence of on-surface reactions. Triggered by thermal annealing, the on-surface reac-tions induced in this experiment involve firstly the coupling of the chiral reactants into chiral polymers and subsequently their transformation into planar prochiral graphene nanoribbons. Our study reveals that the axial chirality of the reactant is not only transferred to the polymers, but also to the planar chirality of the graphene nanoribbon end products. Such chirality transfer consequently allows, starting from ad-equate enantioenriched reactants, for the controlled production of chiral and prochiral organic nanoarchi-tectures with pre-defined handedness

Steering alkyne homocoupling with on-surface synthesized catalysts

We report a multi-step on-surface synthesis strategy. The first step consists in the surface-supported synthesis of metal-organic complexes, which are subsequently used as catalysts to steer on-surface alkyne coupling reactions. In addition, we analyze and compare the electronic properties of the different coupling motifs obtained

Electronic decoupling of polyacenes from the underlying metal substrate by sp ³ carbon atoms

We report on the effect of sp3 hybridized carbon atoms in acene derivatives adsorbed on metal surfaces, namely decoupling the molecules from the supporting substrates. In particular, we have used a Ag(100) substrate and hydrogenated heptacene molecules, in which the longest conjugated segment determining its frontier molecular orbitals amounts to five consecutive rings. The non-planarity that the sp3 atoms impose on the carbon backbone results in electronically decoupled molecules, as demonstrated by the presence of charging resonances in dI/dV tunneling spectra and the associated double tunneling barriers, or in the Kondo peak that is due to a net spin S=1/2 of the molecule as its LUMO becomes singly charged. The spatially dependent appearance of the charging resonances as peaks or dips in the differential conductance spectra is further understood in terms of the tunneling barrier variation upon molecular charging, as well as of the different orbitals involved in the tunneling process

On-surface synthesis of heptacene on Ag(001) from brominated and non-brominated tetrahydroheptacene precursors

Achieving the Ag(001)-supported synthesis of heptacene from two related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy.Fil: Colazzo, Luciano. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Mohammed, Mohammed S. G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Dorel, Ruth. Barcelona Institute of Science and Technology; EspañaFil: Nita, Pawel. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: García Fernández, Carlos. Donostia International Physics Center; EspañaFil: Abufager, Paula Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lorente Palacios, Nicolas. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Echavarren, Antonio M.. Barcelona Institute of Science and Technology; España. Universitat Rovira I Virgili; EspañaFil: De Oteyza, Dimas G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; España. Ikerbasque; Españ

Width-Dependent Band Gap in Armchair Graphene Nanoribbons Reveals Fermi Level Pinning on Au(111)

We report the energy level alignment evolution of valence and conduction bands of armchair-oriented graphene nanoribbons (aGNR) as their band gap shrinks with increasing width. We use 4,4\u2033-dibromo-para-terphenyl as the molecular precursor on Au(111) to form extended poly-para-phenylene nanowires, which can subsequently be fused sideways to form atomically precise aGNRs of varying widths. We measure the frontier bands by means of scanning tunneling spectroscopy, corroborating that the nanoribbon's band gap is inversely proportional to their width. Interestingly, valence bands are found to show Fermi level pinning as the band gap decreases below a threshold value around 1.7 eV. Such behavior is of critical importance to understand the properties of potential contacts in GNR-based devices. Our measurements further reveal a particularly interesting system for studying Fermi level pinning by modifying an adsorbate's band gap while maintaining an almost unchanged interface chemistry defined by substrate and adsorbate

On-Surface Supramolecular Networks: Structure and Dynamics of Formation in Ultra-High Vacuum and at the Solid/Liquid Interface

On-surface supramolecular chemistry inspired the fabrication of a large variety of atomically controlled systems and on-surface synthesis allowed the production of low-dimensional materials with atomic precision. Since numerous surface-supported nanostructures are constantly developed, their possible applications stimulate diverse areas of research such as catalysis, organic electronics, surface sensing, surface functionalization and nanopatterning. Several protocols and interfacial approaches have been developed for the production of surface-supported supramolecular networks by self-assembly and by far, the increasing interest for nanomaterials with innovative functionalities has boosted the search in on-surface activation of chemical reaction for the covalent stabilization of more complex molecular architectures. Photochemistry was furthered as a promising approach for this purpose and pioneering examples allowed a deeper understanding of light-induced on-surface chemical reactions. However, the search in this field is still at its birth and further research is required. The Scanning Tunneling Microscope provides the necessary resolution for this studies in various conditions, including solid/liquid or solid/air interfaces or Ultra High Vacuum (UHV).La chimica supra-molecolare di superficie ha permesso la produzione di numerose nanostrutture tramite l'utilizzo di protocolli di sintesi innovativi. In questo modo si sono ottenuti, tramite controllo strutturale a livello atomico e molecolare, numerosi materiali a ridotta dimensionalità. L'applicazione di tali scoperte si sviluppa nell'ambito della ricerca relativa alla catalisi, all'elettronica organica, alla funzionalizzazione e alla sensibilizzazione della superfici. Poiché esistono diversi approcci per per la produzione di tali strutture, la ricerca ha spinto i propri interessi verso la nano-fabbricazione di materiali per ottenerne, sfruttando varie tecniche, di innovativi, più stabili ed efficienti. La fotochimica di superficie in questo senso, permette di ottenere materiali molto complessi ed inoltre permette di capire i fenomeni alla base dei processi di sintesi indotta dalla luce, che ad oggi, non sono del tutto semplici da interpretare. La microscopia a scansione di tunneling (STM) fornisce l'opportuna risoluzione spaziale per questo tipo di studi, i cui principi sono ancora oggi oggetto di dibattito

First Experiences on Constraining Consistency and Adaptivity of W2000 Models

The complexity of Web applications is increasing almost ev-ery day. Besides impacting the implementation phase, this complexity must also be suitably managed while modeling the application. The paper argues that a pure modeling notation, like W2000, is not enough to cope with such com-plexity and proposes an approach, based on meta-modeling and graph transformation, to enforce the consistency of pro-duced artifacts and adapt them in a controlled way. The paper describes the approach, exemplifies it on some simple examples, and sketches the supporting framework on which we are working

Metal-Free on-Surface Photochemical Homocoupling of Terminal Alkynes

On-surface synthesis involving the homocoupling of aryl-alkynes affords the buildup of bisacetylene derivatives directly at surfaces, which in turn may be further used as ingredients for the production of novel functional materials. Generally, homocoupling of terminal alkynes takes place by thermal activation of molecular precursors on metal surfaces. However, the interaction of alkynes with surface metal atoms often induces unwanted reaction pathways when thermal energy is provided to the system. In this contribution we report about light-induced metal-free homocoupling of terminal alkynes on highly oriented pyrolitic graphite (HOPG). The reaction occurred with high efficiency and selectivity within a self-assembled monolayer (SAM) of aryl-alkynes and led to the generation of large domains of ordered butadiynyl derivatives. Such a photochemical uncatalyzed pathway represents an original approach in the field of topological C\u2013C coupling at the solid/liquid interface

A long-range ordered array of copper tetrameric units embedded in an on-surface metal organic framework

We report on the assembly of a highly ordered array of copper tetrameric clusters, coordinated into a metal-organic network. The ordered cluster array has been achieved by the deposition of tetrahydroxyquinone molecules on the Cu(111) surface at room temperature, and subsequent thermally activated dehydrogenation with the formation of tetraoxyquinone tetra-anions with a 4 x 4 periodicity. The supramolecular organic network acts as a spacer for the highly ordered two-dimensional network of copper tetramers at the very surface