No abstract

Two-dimensional (2D) molecular porous networks (MPNs) self-assembled on surfaces are of great interest due to their potential applications in nanoscience. [1][2][3] Conventionally, the assembled molecules are held together by non-covalent interactions, [4][5][6][7][8][9][10] among which the hydrogen bond (HB) is frequently adopted for structural controllability owing to its desirable bonding strength, selectivity, and directionality. [1] This strategy has been utilized in both uni- [6] and bimolecular [11][12][13][14][15] systems. Generally speaking, hydrogen bonds of similar bond strength are less versatile than hierarchical ones in tuning the assembled structures. In nature, hierarchical hydrogen-bond systems with disparate bonding capabilities and strengths are widely adopted by biosystems such as DNA and bioactive structures which consist of only limited building blocks. Researchers have utilized metal coordination [16,17] or hydrogen bonds [4,18] to form various porous networks on surfaces. Controls of the network pattern and the resulting pore size and shape can be achieved by tuning parameters [17,[19][20][21] such as ligand chain lengths or molecular backbones, [19] surface coverage [20] and substrate temperature.[22] These strategies have been demonstrated for a number of uni- [16,20] or bimolecular systems. [18,23] For example, by adjusting the metal-to-ligand ratio and the annealing temperature, mononuclear, 1D-polymeric and 2D-reticulated metal-organic coordination networks can be obtained by vapor deposition of 1,4-benzenedicarboxylic acid molecules and iron atoms on a Cu(100) surface, giving rise to an interesting series of square, rectangular and rhombic pores. [16] Another excellent example demonstrating controls of the network pattern and pore morphology is the 2D mono-and bicomponent self-assembly of three closely related diaminotriazine-based molecular building blocks and a complementary perylenetetracarboxylic diimide on Au(111) surface. The interplay, and the hierarchy, of hydrogen bonding, metalligand coordination, and dipolar interactions, resulted in various MPNs. In one case, mixtures of square, rhombic, and hexagonal nanopores were obtained.[24] A third example illustrating the construction of tunable 2D binary molecular nanostructures on an inert surface is the co-deposition of copper hexadecafluorophthalocyanine with p-sexiphenyl, pentacene, or diindenoperylene on graphite. By varying the binary molecular ratio and the molecular geometry, various molecular networks with tunable intermolecular distances were fabricated. [18,25] Yet other studies of porous networks via coadsorption of multi-component or multi-functional adsorbates or solvent incorporation on surfaces, producing a wide variety of interesting nanostructures, can also be found in the literature. [26][27][28][29][30][31] These results offer various routes for fabricating tunable molecular networks with tailorable nanopores potentially useful in engineering molecular sensors, molecular spintronic devices, and molecular nano h...

We report herein the template-directed synthesis, characterization, and electric properties of single-walled carbon nanotube- (SWNT-) based coaxial nanowires, that is, core (SWNT)-shell (conducting polypyrrole and polyaniline) nanowires. The SWNTs were first dispersed in aqueous solutions containing cationic surfactant cetyltrimethylammonium bromide (CTAB) or nonionic surfactant poly(ethylene glycol) mono-p-nonyl phenyl ether (O pi-10). Each individual nanotube (or small bundle) was then encased in its own micellelike envelope with hydrophobic surfactant groups orientated toward the nanotube and hydrophilic groups orientated toward the solution. And thus a hydrophobic region within the micelle/SWNT (called a micelle/SWNT hybrid template) was formed. Insertion and growth of pyrrole or aniline monomers in this hybrid template, upon removal of the surfactant, produce coaxial structures with a SWNT center and conducting polypyrrole or polyaniline coating. Raman and Fourier transform infrared (FTIR) spectroscopy and scanning (SEM) and transmission (TEM) electron microscopy were used to characterize the composition and the structures of these coaxial nanowires. The results revealed that the micellar molecules used could affect the surface morphologies of the resulting coaxial nanowires but not the molecular structures of the corresponding conducting polymers. Electric properties testing indicated that the SWNTs played the key roles in the conducting polymer/SWNT composites during electron transfer in the temperature range 77 K to room temperature. Compared with the SWNT network embedded in the conducting polymers, the composites within which SWNTs were coated perfectly by the identical conducting polymers exhibited higher barrier heights during electron transfer.

No abstract

Two-dimensional (2D) molecular porous networks (MPNs) self-assembled on surfaces are of great interest due to their potential applications in nanoscience. [1][2][3] Conventionally, the assembled molecules are held together by non-covalent interactions, [4][5][6][7][8][9][10] among which the hydrogen bond (HB) is frequently adopted for structural controllability owing to its desirable bonding strength, selectivity, and directionality. [1] This strategy has been utilized in both uni- [6] and bimolecular [11][12][13][14][15] systems. Generally speaking, hydrogen bonds of similar bond strength are less versatile than hierarchical ones in tuning the assembled structures. In nature, hierarchical hydrogen-bond systems with disparate bonding capabilities and strengths are widely adopted by biosystems such as DNA and bioactive structures which consist of only limited building blocks. Researchers have utilized metal coordination [16,17] or hydrogen bonds [4,18] to form various porous networks on surfaces. Controls of the network pattern and the resulting pore size and shape can be achieved by tuning parameters [17,[19][20][21] such as ligand chain lengths or molecular backbones, [19] surface coverage [20] and substrate temperature.[22] These strategies have been demonstrated for a number of uni- [16,20] or bimolecular systems. [18,23] For example, by adjusting the metal-to-ligand ratio and the annealing temperature, mononuclear, 1D-polymeric and 2D-reticulated metal-organic coordination networks can be obtained by vapor deposition of 1,4-benzenedicarboxylic acid molecules and iron atoms on a Cu(100) surface, giving rise to an interesting series of square, rectangular and rhombic pores. [16] Another excellent example demonstrating controls of the network pattern and pore morphology is the 2D mono-and bicomponent self-assembly of three closely related diaminotriazine-based molecular building blocks and a complementary perylenetetracarboxylic diimide on Au(111) surface. The interplay, and the hierarchy, of hydrogen bonding, metalligand coordination, and dipolar interactions, resulted in various MPNs. In one case, mixtures of square, rhombic, and hexagonal nanopores were obtained.[24] A third example illustrating the construction of tunable 2D binary molecular nanostructures on an inert surface is the co-deposition of copper hexadecafluorophthalocyanine with p-sexiphenyl, pentacene, or diindenoperylene on graphite. By varying the binary molecular ratio and the molecular geometry, various molecular networks with tunable intermolecular distances were fabricated. [18,25] Yet other studies of porous networks via coadsorption of multi-component or multi-functional adsorbates or solvent incorporation on surfaces, producing a wide variety of interesting nanostructures, can also be found in the literature. [26][27][28][29][30][31] These results offer various routes for fabricating tunable molecular networks with tailorable nanopores potentially useful in engineering molecular sensors, molecular spintronic devices, and molecular nano h...