Showing papers by "Dong Wang published in 2010"

Engineering of linear molecular nanostructures by a hydrogen-bond-mediated modular and flexible host-guest assembly.

Abstract: The formation of a desired nanostructure with concomitant patterns and functions is of utmost importance in the field of surface molecular engineering and nanotechnology. We here present a flexible host−guest assembly, which steers the formation of linear molecular nanostructures on surfaces by a hydrogen-bond-mediated assembly process. A linear monodendron molecular template with periodic hydrogen-bond binding sites is shown to accommodate a variety of molecules with pyridylethynyl terminals. The unit cell parameters in the transverse direction of the linear pattern can be tuned from 3.4 to 7.3 nm in response to the packing of the guest molecules with different sizes, shapes, and aggregation number. The introduction of hydrogen-bonding partners into the host template and into guest molecules is responsible for the steering of the linear pattern of guest molecules. The modular approach could greatly facilitate the ordering of guest molecules with desired functional moieties.

Spontaneous growth of free-standing polypyrrole films at an air/ionic liquid interface.

Abstract: A novel strategy for the one-pot fabrication of free-standing polypyrrole films is presented in this work. The films are spontaneously formed at an air/ionic liquid interface through interface oxypolymerization. The thicknesses of the films are finely controlled from tens to hundreds of nanometers, and the films are uniform and compact. Asymmetrical films with different smoothness on the two sides of the film are also obtained and exhibit different water wettability. This method is extremely simple and does not need any equipment. It may bring about a general methodology for forming free-standing conducting polymer films.

Formation and structural transition of molecular self-assembly on solid surface investigated by scanning tunneling microscopy

Abstract: The spontaneous formation of ordered self-assembly on solid supports is not only an intriguing subject for fundamental surface science study, but also closely related to many emerging technologically important applications, especially in the field of nanotechnology. With the help of scanning tunneling microscopy (STM) at sub-molecular resolution, the detailed structural information within the self-assembled monolayers can be obtained, which allows us to have an insight into how the interplay between the intermolecular weak interactions and the substrate–molecule interactions governs the formation of molecular self-assembly. In this review, the structural transition of self-assembly in response to the subtle differences in the molecular structures and/or the environment change will be presented. The fundamental understanding about the driving force controlling the assembly process promotes the development of various means to tune the structural transition of supramolecular assembly on solid surfaces and fabricate the sophisticated architectures. Finally, some future directions in the field are outlined.

In Situ Scanning Tunneling Microscopy of Solvent-Dependent Chiral Patterns of 1,4-Di[4-N-(trihydroxymethyl)methyl carbamoylphenyl]-2,5-didodecyloxybenzene Molecular Assembly at a Liquid/Highly Oriented Pyrolytic Graphite Interface

Abstract: Solvent effect on chirality of 1,4-di[4-N-(trihydroxymethyl)methyl carbamoylphenyl]-2,5-didodecyloxybenzene (DTCD) self-assembled adlayer on highly oriented pyrolytic graphite (HOPG) is investigated by in situ scanning tunneling microscopy using tetrahydrofuran (THF), 1-phenyloctane (PO), 1-octanol, and 1,2,4-trichlorobenzene (TCB) as solvent. Different chiral patterns are acquired in these solvents, suggesting that the chiral assembly of DTCD is solvent-dependent. With use of THF or PO as solvent, chiral patterns with windmill-shaped tetramer units are observed. In contrast, a racemic lamellar structure is revealed in 1-octanol. The coadsorption of 1-octanol molecules makes an important contribution to the formation of racemic lamellar structure. A structure transition from racemic lamellar structure to tetramer-based chiral patterns is observed with removal of 1-octanol molecules by thermal annealing. When TCB is used as solvent, a chiral meshy structure is formed at the TCB/HOPG interface. The results ...

EEHG-assisted FEL schemes for attosecond X-ray pulses generation

Abstract: In this paper, the schemes of echo-enabled harmonic generation (EEHG) assisted free electron laser (FEL) for generating attosecond soft X-ray pulses are further investigated. We present brief analytical models and three-dimensional simulations for comparison studies of such schemes reported earlier. Moreover, on the basis of these analyses, a more compact and robust EEHG-assisted FEL scheme is proposed for pump-probe experiments using two-color attosecond X-ray pulses.

Study on Lewis acid promoted condensation of allylalkoxysilanes with (‐)‐menthyl glyoxylate

Abstract: Allylalkoxydimethylsilanes (2) condense with (-)-menthyl glyoxylate (3) in the presence of Lewis acid to give optically active menthyl 2-hydroxy-4-pentenoate (7) with optical purity of 31–42%. Factors affecting the yield and de of 7 have been examined. The stereochemistry of transition state of the reaction was discussed.

Catalyst-free tandem Michael addition-cyclization reactions in aqueous media for the synthesis of benzimidazo[1,2-a]pyrimidinone derivatives

Abstract: The catalyst-free reactions of Baylis-Hillman alcohols (1a-i) with 2-aminobenzimidazole (2) in THF-H2O (1:4) were developed for the convenient and greener synthesis of benzimidazo[1,2-a]pyrimidinone derivatives (3a-i). The pesticidal activities of 3a-i were examined to investigate a new biological activity of the imidazo[1,2-a]pyrimidinone-type compounds.

Asymmetric allylation of aldehydes and alkylation using “carbon-centered” chiral organosilicon compounds

Abstract: The effects of the chiral substituents attached to silicon on the stereoselectivity of the reactions of C-centered chiral silicon compounds wm examined. The investigation was focused on the asymmetric C—C bond formation reaction of chiral allylsilanes and α-silylallyl anions with aldehydes. The functionalities of the substituents on silicon can be manipulated to improve the stereoselectivities of the reactions remote from silicon atom.

Surface host-guest assembly as a bottom-up approach for the construction of functional molecular nanostructures

Abstract: Surface host-guest assembly is a promising bottom-up approach to build up molecular nanostructures with good controllability In the present study, we investigated the solvent effect on the host-guest assembly of 2,7,12-trihexyloxytruxene (Tr) with coronene by scanning tunneling microscopy at liquid/solid interfaces The two-dimensional (2D) self-assembled networks of Tr are shown to accommodate coronene guest molecules on highly oriented pyrolytic graphite (HOPG) surfaces In contrast to the similar 2D hexagonal self-assembly of Tr host template on HOPG in different solvents, the formation of host-guest nanostructures of coronene in Tr 2D network strongly depend on the polarity of the solvents The thermodynamic equilibrium during the host-guest assembly process is discussed, and the solvent-guest interaction is proposed as a main contributor for the observed solvent effect in the 2D host-guest self-assembly process