Haiming Zhang

Linear Alkane Polymerization on a Gold Surface

The confining channel geometry of a gold surface induces selective end-to-end linking of hydrocarbon chains. In contrast to the many methods of selectively coupling olefins, few protocols catenate saturated hydrocarbons in a predictable manner. We report here the highly selective carbon-hydrogen (C–H) activation and subsequent dehydrogenative C–C coupling reaction of long-chain (>C20) linear alkanes on an anisotropic gold(110) surface, which undergoes an appropriate reconstruction by adsorption of the molecules and subsequent mild annealing, resulting in nanometer-sized channels (1.22 nanometers in width). Owing to the orientational constraint of the reactant molecules in these one-dimensional channels, the reaction takes place exclusively at specific sites (terminal CH3 or penultimate CH2 groups) in the chains at intermediate temperatures (420 to 470 kelvin) and selects for aliphatic over aromatic C–H activation.

On-Surface Synthesis of Rylene-Type Graphene Nanoribbons

The narrowest armchair graphene nanoribbon (AGNR) with five carbons across the width of the GNR (5-AGNR) was synthesized on Au(111) surfaces via sequential dehalogenation processes in a mild condition by using 1,4,5,8-tetrabromonaphthalene as the molecular precursor. Gold-organic hybrids were observed by using high-resolution scanning tunneling microscopy and considered as intermediate states upon AGNR formation. Scanning tunneling spectroscopy reveals an unexpectedly large band gap of Δ = 2.8 ± 0.1 eV on Au(111) surface which can be interpreted by the hybridization of the surface states and the molecular states of the 5-AGNR.

Surface Supported Gold–Organic Hybrids: On‐Surface Synthesis and Surface Directed Orientation

The surface-assisted synthesis of gold-organic hybrids on Au (111) and Au (100) surfaces is repotred by thermally initiated dehalogenation of chloro-substituted perylene-3,4,9,10-tetracarboxylic acid bisimides (PBIs). Structures and surface-directed alignment of the Au-PBI chains are investigated by scanning tunnelling microscopy in ultra high vacuum conditions. Using dichloro-PBI as a model system, the mechanism for the formation of Au-PBI dimer is revealed with scanning tunnelling microscopy studies and density functional theory calculations. A PBI radical generated from the homolytic C-Cl bond dissociation can covalently bind a surface gold atom and partially pull it out of the surface to form stable PBI-Au hybrid species, which also gives rise to the surface-directed alignment of the Au-PBI chains on reconstructed Au (100) surfaces.

Surface-Controlled Mono/Diselective ortho C–H Bond Activation

One of the most charming and challenging topics in organic chemistry is the selective C-H bond activation. The difficulty arises not only from the relatively large bond-dissociation enthalpy, but also from the poor reaction selectivity. In this work, Au(111) and Ag(111) surfaces were used to address ortho C-H functionalization and ortho-ortho couplings of phenol derivatives. More importantly, the competition between dehydrogenation and deoxygenation drove the diversity of reaction pathways of phenols on surfaces, that is, diselective ortho C-H bond activation on Au(111) surfaces and monoselective ortho C-H bond activation on Ag(111) surfaces. The mechanism of this unprecedented phenomenon was extensively explored by scanning tunneling microscopy, density function theory, and X-ray photoelectron spectroscopy. Our findings provide new pathways for surface-assisted organic synthesis via the mono/diselective C-H bond activation.

Two-Dimensional Chirality Transfer via On-Surface Reaction

Two-dimensional chirality transfer from self-assembled (SA) molecules to covalently bonded products was achieved via on-surface synthesis on Au(111) substrates by choosing 1,4-dibromo-2,5-didodecylbenzene (12DB) and 1,4-dibromo-2,5-ditridecylbenzene (13DB) as designed precursors. Scanning tunneling microscopy investigations reveal that their aryl-aryl coupling reaction occurs by connecting the nearest neighboring precursors and thus preserving the SA lamellar structure. The SA structures of 12(13)DB precursors determine the final structures of produced oligo-p-phenylenes (OPP) on the surface. Pure homochiral domains (12DB) give rise to homochiral domains of OPP, whereas lamellae containing mixed chiral geometry of the precursor (13DB) results in the formation of racemic lamellae of OPP.

Ion Strength and pH Sensitive Phase Transition of N-Isobutyryl-l-(d)-cysteine Monolayers on Au(111) Surfaces

Self-assembled monolayers (SAMs) of N-isobutyryl-L-(D)-cysteine (NIBC) on Au(111) surfaces were successfully prepared by immersing the Au(111) surfaces in the preheated pure NIBC aqueous solutions for a certain time and characterized by means of scanning tunneling microscopy. Close-packed lamellar structures with a rectangular (4 x radical3) lattice were found both in the SAMs of L-NIBC and D-NIBC. The pH value of the aqueous solutions was found to be sensitive to adjust the SAM structures during the assembly. Changing the pH value from 5 to 7 may completely shift the SAM structures from close-packed lamellar phase to loose-packed perpendicular phase. Combined with density functional theory calculations, such kind of phase transition was explained by the breaking of hydrogen bonds between carboxylic groups and the formation of extra interactions between COO(-) and Au.

Precursor adsorption of SbBr3 on au(111) and au(100) for antimony underpotential deposition in a BMIBF4 ionic liquid a comparison with SbCl3

By employing in-situ STM, we have studied precursor adsorption and initial stage of Sb UPD on Au(111) and Au(100) in a SbBr3-containing BMIBF4 ionic liquid. It has been observed that the adsorption of SbBr3 selectively takes place on Au(100), in contrast to that of SbCl3, with formation of chains with structure as well as squares with structure. The chains are composed of pairs of SbBr3 molecules, which are bridged with the adjacent SbBr3 molecules in the chain to form the anisotropy along either of the two characteristic directions of Au(100). The square configured structure is composed of periodically arranged monomeric and dimeric SbBr3, which will gradually replace the chain structure. Regardless of the precursor adsorption, however, the initial stage of Sb UPD is characterized by the formation of atomic strips, like in the SbCl3-containing system, which reveals the consistency of discharging behavior of Sb(III) from the SbCl3 and SbBr3 molecules. Together with the findings from the SbCl3-containing system, the results are discussed in view of matching of structures between the pyramidal antimony tri-halides and the crystalline surfaces. The role of the ionic liquid as well as properties of the electrified interface will also be mentioned.