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We demonstrate that the strong N2 bond can be efficiently dissociated at low pressure and ambient temperature on a Si(111)-7x7 surface. The reaction was experimentally investigated by scanning tunnelling microscopy and X-ray photoemission spectroscopy. Experimental and density functional theory results suggest that relatively low thermal energy collision of N2 with the surface can facilitate electron transfer from the Si(111)-7x7 surface to the π*-antibonding orbitals of N2 that significantly weaken the N2 bond. This activated N2 triple bond dissociation on the surface leads to the formation of a Si3 N interface.
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The detection of organophosphates, a wide class of pesticides, in water-solution has a huge impact in environmental monitoring. Acoustic transducers are used to design passive wireless sensors for the direct detection of pesticides in water-solution by using tailored polymers as sensitive layers. We demonstrate by combining analytical chemistry tools that organophosphate molecules strongly alter polymer layers widely used in acoustic sensors in the presence of water. This chemical degradation can limit the use of these polymers in detection of organophosphates in water-solution.
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Clorpirifos , Praguicidas , Acústica , Praguicidas/análise , Polímeros , ÁguaRESUMO
We developed a new class of mono- or few-layered two-dimensional polymers based on dinuclear (arene)ruthenium nodes, obtained by combining the imine condensation with an interfacial chemistry process, and use a modified Langmuir-Schaefer method to transfer them onto solid surfaces. Robust nano-sheets of two-dimensional polymers including dinuclear complexes of heavy ruthenium atoms as nodes were synthesised. These nano-sheets, whose thickness is of a few tens of nanometers, were suspended onto solid porous membranes. Then, they were thoroughly characterised with a combination of local probes, including Raman spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy in imaging and diffraction mode.
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The growth of an extended supramolecular network using dipolar molecules as the building blocks is of great technological interest. We investigated the self-assembly of a dipolar molecule on an Au(111) surface. The formation of an extended two-dimensional network was demonstrated by scanning tunnelling microscopy under ultra-high vacuum and explained in terms of molecule-molecule interactions. This 2D-network is still stable under the pressure of one atmosphere of nitrogen, which demonstrated its interest for the development of submolecular-precisely polyfunctional smart surfaces.
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A class of two-dimensional (2D) covalent organometallic polymers, with nanometer-scale crosslinking, was obtained by arene(ruthenium) sulfur chemistry. Their ambivalent nature, with positively charged crosslinks and lypophylic branches is the key to the often sought-for and usually hard-to-achieve solubility of 2D polymers in various kinds of solvents. Solubility is here controlled by the planarity of the polymer, which in turn controls Coulomb interactions between the polymer layers. High planarity is achieved for high symmetry crosslinks and short, rigid branches. Owing to their solubility, the polymers are easily processable, and can be handled as powder, deposited on surfaces by mere spin-coating, or suspended across membranes by drop-casting. The novel 2D materials are potential candidates as flexible membranes for catalysis, cancer therapy, and electronics.
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In the last decade, many nanomachines with controlled molecular motions have been studied, mainly on metallic surfaces, which are easy to obtain very clean, and are stable over months. However, the studies of mechanical properties of nanomachines are mainly performed at very low temperatures, usually between 5 and 80â K, which prevents any kind of applications. In this Minireview, we will present our strategy to operate at higher temperatures, in particular through the use of semiconducting silicon surfaces. We also review our best achievements in the field through some examples of rotating molecular machines that have been designed, synthesized, and studied in our groups. On metallic surfaces, the nanovehicles are molecules with two or four triptycenes as wheels and the molecular motor is built around a ruthenium organometallic center with a piano-stool geometry and peripheric ferrocenyl groups. On semiconducting silicon surfaces, vehicles are also made from triptycene fragments and the rotor is a pentaphenylbenzene molecule.
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High-density packing in organic crystals is usually associated with an increase of the coordination between molecules. Such a concept is not necessarily extended to two-dimensional molecular networks self-assembled on a solid surface, for which we demonstrate the key role of the surface in inducing the optimal packing. By a combination of scanning tunneling microscopy experiments and multiscale computer simulations, we study the phase transition between two polymorphs. We find that, contrary to intuition, the structure with the lowest packing fraction corresponds to the highest molecular coordination number, due to the competition between surface and intermolecular forces. Having the lowest free energy, this structure spreads out as the most stable polymorph over a wide range of molecular concentrations.
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Thermally activated rotation of single molecules adsorbed on a silicon-based surface between 77 and 150 K has been successfully achieved. This remarkable phenomenon relies on a nanoporous supramolecular network, which acts as a template to seed periodic molecule rotors on the surface. Thermal activation of rotation has been demonstrated by STM experiments and confirmed by theoretical calculations.
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The controlled growth of self-assembled networks on surfaces based on viologen salts is a major scientific challenge due to their unique electronic properties. The combination of solid-state NMR spectroscopy and atomic force microscopy at ambient conditions can unravel the fine organization of the supramolecular network on a graphitic surface by positioning the counter-ions relative to the viologen cation.
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The design of supramolecular networks based on organic molecules deposited on surfaces, is highly attractive for various applications. One of the remaining challenges is the expansion of monolayers to well-ordered multilayers in order to enhance the functionality and complexity of self-assemblies. In this study, we present an assessment of molecular conformation from 2D to 3D supramolecular networks adsorbed onto a HOPG surface under ambient conditions utilizing a combination of scanning probe microscopies and atomic force microscopy- infrared (AFM-IR). We have observed that the infrared (IR) spectra of the designed molecules vary from layer to layer due to the modifications in the dihedral angle between the C=O group and the neighboring phenyl ring, especially in the case of a 3D supramolecular network consisting of multiple layers of molecules.
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Polymers obtained by on-surface chemistry have emerged as a class of promising materials. Here, we propose a new strategy to obtain self-assembled 1D polymers by using photochemical [2+2] cyclo-addition or by using a mild thermal annealing. All nanostructures are fully characterized by using scanning tunneling microscopy at ambient conditions on a graphite surface. We demonstrated that nature of the stimulus strongly alters the overall quality of the resulting polymers in terms of length and number of defects. This new way is an efficient method to elaborate on-surface self-assembled 1D polymers.
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The growth of graphene nanoribbons has been widely investigated on metal surfaces in an ultrahigh vacuum. Here, we re-investigate the growth of graphene nanoribbons obtained by thermal annealing of 9,9'-bianthryl derivatives on a Cu(111) surface by using scanning tunnelling microscopy. On the basis of our results, we propose to complete the reaction mechanism commonly accepted in the literature by adding an intramolecular hydrogen atom transfer from the 2,2'-positions to the 10,10'-positions as a key-step in the formation of (3,1)-graphene nanoribbons on a Cu(111) surface.
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On-surface metal-organic polymers have emerged as a class of promising 2D materials. Here, we propose a new strategy to obtain coordination polymers by transforming supramolecular networks into coordination polymers by surface-assisted cyclo-dehydrogenation of organic building blocks. All nanostructures are fully characterized by using scanning tunneling microscopy under ultra-high vacuum on a gold surface. We demonstrated that the balance between molecule-molecule interaction and molecule-substrate interaction can be drastically modified by a strong modification of the geometry of the molecules thanks to a thermal annealing. This new way is an efficient method to elaborate on-surface coordination polymers.
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Over the past decade, on-surface fabrication of organic nanostructures has been widely investigated for the development of molecular electronic components, catalysts, and new materials. Here, we introduce a new strategy to obtain alkyl oligomers in a controlled manner using on-surface radical oligomerisations that are triggered by electrons between the tip of a scanning tunnelling microscope and the Si(111)â3 ×â3 R30°-B surface. This electron transfer event only occurs when the bias voltage is below -4.5 V and allows access to reactive radical species under exceptionally mild conditions. This transfer can effectively 'switch on' a sequence leading to the formation of oligomers of defined size distribution thanks to the on-surface confinement of the reactive species. Our approach enables new ways to initiate and control radical oligomerisations with tunnelling electrons, leading to molecularly precise nanofabrication.
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A single 4-pyridylazobenzene molecule is observed at room temperature on a Si(111)-B surface by using scanning tunnel microscopy. The reversible conformational switching of this molecule is induced by tunneling electrons and observed at room temperature. This process is based on an intramolecular rotation of a single phenyl group without isomerization of the N=N double bond.
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The formation of compact and large-scale self-assembled monolayers (SAMs) adsorbed on a mica surface has been achieved by insertion of alkyl chains on azobenzene derivatives, leading to strong intermolecular van der Waals interactions and hydrogen bonding. The reversible photoswitching of monolayers was investigated by monitoring the variation of the thickness of the SAMs during the cis-trans isomerization of the azobenzene cores with an atomic force microscope (AFM). The absence of covalent bonds between molecules and substrate induces a molecular diffusion which leads to the complete isomerization of the molecules constituting the SAMs.
Assuntos
Silicatos de Alumínio/química , Compostos Azo/química , Membranas Artificiais , Fotoquímica/métodos , Adsorção , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Microscopia de Força Atômica , Modelos Teóricos , Espectrofotometria Ultravioleta , Raios UltravioletaRESUMO
We have investigated the self-assembly of a strong dipolar molecule (LDipCC) on the semiconducting Si(111)-B surface with scanning tunneling microscopy (STM), density functional theory (DFT) calculations and STM simulations. Although the formation of an extended two-dimensional network was clearly revealed by STM under ultra-high vacuum, the assignment of a specific STM signature to the different terminal groups from the LDipCC molecular unit required a complete analysis by numerical simulations. The overall observed assembly is explained in terms of STM contrasts associated with the molecular structure of LDipCC and the molecule-surface interactions. To distinguish the relative arrangement of the dipolar molecules within the assembly, a rational combination of experimental results and electronic structure calculations allows us to identify a single adsorbed LDipCC phase in which the molecular dipoles are homogeneously arranged into a parallel fashion on the Si(111)-B surface.
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The engineering of a complete adlayer of organic nanolines by supramolecular self-assembly has been achieved for the first time on a silicon-based surface at room temperature and has been studied by scanning tunneling microscopy. This complete adlayer has been successfully obtained thanks to the combination of a specific Si(111)-B square root 3x square root 3R30 degrees semiconductive surface and of strong hydrogen bonds between a pair of dipolar molecules.
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This work describes an innovative concept for the development of organized molecular systems based on the template effect of the pre-structured semi-conductive SmSi(111) interface. This substrate is selected because Sm deposition in the submonolayer range leads to a 8x2-reconstruction, which is a well-defined one-dimensional semi-metallic structure. Adsorption of aromatic molecules [1,4-di-(9-ethynyltriptycenyl)-benzene] on SmSi(111)- 8x2 and Si(111)-7x7 interfaces is investigated by scanning tunneling microscopy (STM) at room temperature. Density functional theory (DFT) and semi-empirical (ASED+) calculations define the nature of the molecular adsorption sites of the target molecule on SmSi as well as their self-alignment on this interface. Experimental data and theoretical results are in good agreement.