Interaction of Chiral and Achiral Dimethylsuccinic Acid Diastereomers with a Cu(110) Surface

The transmission of chirality to an achiral metal surface after adsorption of chiral or achiral molecules is an exciting approach toward new materials systems. The interaction of racemic 2,3-dimethylsuccinic acid and its achiral meso form with a Cu(110) surface has been investigated in ultrahigh vacuum by means of X-ray photoelectron spectroscopy, low-energy electron diffraction, reflection absorption infrared spectroscopy, scanning tunneling microscopy, temperature-programmed desorption, and density functional theory. Racemic as well as meso-2,3-dimethylsuccinic acid form extended enantiomorphous structures, coexisting with extended two-dimensional structures that do not break the mirror symmetry of the substrate surface. Copper adatoms decorating the molecules suggest a chiral reconstruction of the surface. The thermally induced decomposition proceeds autocatalytically in a so-called surface explosion and shows a profound difference for the diastereomers

Chiral Surface from Achiral Ingredients: Modification of Cu(110) with Phthalic Acid

The adsorption of dicarboxylic acids is a classical model approach for understanding molecular recognition at surfaces. The interaction of achiral phthalic acid with an achiral Cu(110) surface has been investigated in ultrahigh vacuum by means of scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy, reflection absorption infrared spectroscopy, temperature-programmed desorption, and density functional theory. Different ordered domains at a length scale of several tens of nanometers are observed, of which three are enantiomorphous and therefore appear in two mirror-symmetric forms. Theoretical considerations suggest that spontaneous mirror-symmetry breaking occurs at the single-molecular level, in which the surface becomes also chirally distorted

On-Surface Synthesis of Square-Type Porphyrin Tetramers with Central Antiaromatic Cyclooctatetraene Moiety

The synthesis of two-dimensionally extended polycyclic heteroatomic molecules keeps attracting considerable attention. In particular, frameworks bearing planar cyclooctatetraenes (COT) moieties can display intriguing properties, including antiaromaticity. Here, we present an on-surface chemistry route to square-type porphyrin tetramers with a central COT ring, coexisting with other oligomers. This approach employing temperature-induced dehydrogenative porphyrin homocoupling in an ultrahigh vacuum environment provides access to surface-supported, unsubstituted porphyrin tetramers that are not easily achievable by conventional synthesis means. Specifically, monomeric free-base (2H-P) and Zn-metalated (Zn-P) porphines (P) were employed to form square-type free-base and Zn-functionalized tetramers on Ag(100). An atomic-level characterization by bond-resolved atomic force microscopy and scanning tunneling microscopy and spectroscopy is provided, identifying the molecular structures. Complemented by density functional theory modeling, the electronic structure is elucidated, indeed revealing antiaromaticity induced by the COT moiety. The present study thus gives access, and insights, to a porphyrin oligomer, representing both a model system for directly fused porphyrins and a potential building block for conjugated, extended two-dimensional porphyrin sheets

On-Surface Synthesis of a Radical 2D Supramolecular Organic Framework

The design of supramolecular organic radical cages and frameworks is one of the main challenges in supramolecular chemistry. Their interesting material properties and wide applications make them very promising for (photo)redox catalysis, sensors, or host–guest spin–spin interactions. However, the high reactivity of radical organic systems makes the design of such supramolecular radical assemblies challenging. Here, we report the on-surface synthesis of a purely organic supramolecular radical framework on Au(111), by combining supramolecular and on-surface chemistry. We employ a tripodal precursor, functionalized with 7-azaindole groups that, catalyzed by a single gold atom on the surface, forms a radical molecular product constituted by a π-extended fluoradene-based radical core. The radical products self-assemble through hydrogen bonding, leading to extended 2D domains ordered in a Kagome-honeycomb lattice. This approach demonstrates the potential of on-surface synthesis for developing 2D supramolecular radical organic chemistry

Selective Activation of Aromatic C–H Bonds Catalyzed by Single Gold Atoms at Room Temperature

Selective activation and controlled functionalization of C–H bonds in organic molecules is one of the most desirable processes in synthetic chemistry. Despite progress in heterogeneous catalysis using metal surfaces, this goal remains challenging due to the stability of C–H bonds and their ubiquity in precursor molecules, hampering regioselectivity. Here, we examine the interaction between 9,10-dicyanoanthracene (DCA) molecules and Au adatoms on a Ag(111) surface at room temperature (RT). Characterization via low-temperature scanning tunneling microscopy, spectroscopy, and noncontact atomic force microscopy, supported by theoretical calculations, revealed the formation of organometallic DCA–Au–DCA dimers, where C atoms at the ends of the anthracene moieties are bonded covalently to single Au atoms. The formation of this organometallic compound is initiated by a regioselective cleaving of C–H bonds at RT. Hybrid quantum mechanics/molecular mechanics calculations show that this regioselective C–H bond cleaving is enabled by an intermediate metal–organic complex which significantly reduces the dissociation barrier of a specific C–H bond. Harnessing the catalytic activity of single metal atoms, this regioselective on-surface C–H activation reaction at RT offers promising routes for future synthesis of functional organic and organometallic materials

Chemical Identification of Single Atoms in Heterogeneous III–IV Chains on Si(100) Surface by Means of nc-AFM and DFT Calculations

Chemical identification of individual atoms in mixed In–Sn chains grown on a Si(100)-(2 × 1) surface was investigated by means of room temperature dynamic noncontact AFM measurements and DFT calculations. We demonstrate that the chemical nature of each atom in the chain can be identified by means of measurements of the short-range forces acting between an AFM tip and the atom. On the basis of this method, we revealed incorporation of silicon atoms from the substrate into the metal chains. Analysis of the measured and calculated short-range forces indicates that even different chemical states of a single atom can be distinguished

Chemical Identification of Single Atoms in Heterogeneous III–IV Chains on Si(100) Surface by Means of nc-AFM and DFT Calculations

Chemical identification of individual atoms in mixed In–Sn chains grown on a Si(100)-(2 × 1) surface was investigated by means of room temperature dynamic noncontact AFM measurements and DFT calculations. We demonstrate that the chemical nature of each atom in the chain can be identified by means of measurements of the short-range forces acting between an AFM tip and the atom. On the basis of this method, we revealed incorporation of silicon atoms from the substrate into the metal chains. Analysis of the measured and calculated short-range forces indicates that even different chemical states of a single atom can be distinguished

Chemical Identification of Single Atoms in Heterogeneous III–IV Chains on Si(100) Surface by Means of nc-AFM and DFT Calculations

Chemical identification of individual atoms in mixed In–Sn chains grown on a Si(100)-(2 × 1) surface was investigated by means of room temperature dynamic noncontact AFM measurements and DFT calculations. We demonstrate that the chemical nature of each atom in the chain can be identified by means of measurements of the short-range forces acting between an AFM tip and the atom. On the basis of this method, we revealed incorporation of silicon atoms from the substrate into the metal chains. Analysis of the measured and calculated short-range forces indicates that even different chemical states of a single atom can be distinguished

Chemical Identification of Single Atoms in Heterogeneous III–IV Chains on Si(100) Surface by Means of nc-AFM and DFT Calculations

Chemical identification of individual atoms in mixed In–Sn chains grown on a Si(100)-(2 × 1) surface was investigated by means of room temperature dynamic noncontact AFM measurements and DFT calculations. We demonstrate that the chemical nature of each atom in the chain can be identified by means of measurements of the short-range forces acting between an AFM tip and the atom. On the basis of this method, we revealed incorporation of silicon atoms from the substrate into the metal chains. Analysis of the measured and calculated short-range forces indicates that even different chemical states of a single atom can be distinguished

Chemical Identification of Single Atoms in Heterogeneous III–IV Chains on Si(100) Surface by Means of nc-AFM and DFT Calculations

Chemical identification of individual atoms in mixed In–Sn chains grown on a Si(100)-(2 × 1) surface was investigated by means of room temperature dynamic noncontact AFM measurements and DFT calculations. We demonstrate that the chemical nature of each atom in the chain can be identified by means of measurements of the short-range forces acting between an AFM tip and the atom. On the basis of this method, we revealed incorporation of silicon atoms from the substrate into the metal chains. Analysis of the measured and calculated short-range forces indicates that even different chemical states of a single atom can be distinguished