Self-Assembling Properties of 11-Ferrocenyl-1-Undecanethiol on Highly Oriented Pyrolitic Graphite Characterized by Scanning Tunneling Microscopy (original) (raw)
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Chemistry – A European Journal, 2012
The synthesis and structures of the N‐[(2‐hydroxy‐3‐methyl‐5‐dodecylphenyl)methyl]‐N‐(carboxymethyl)glycine disodium salt (HL) ligand and its neutral mononuclear complex [FeIII(L)(EtOH)2] (1) are reported. Structural and electronic properties of 1 were investigated by using scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS) techniques. These studies reveal that molecules of 1 form well‐ordered self‐assemblies when deposited on a highly oriented pyrolytic graphite (HOPG) surface. At low concentrations, single or double chains (i.e., nanowires) of the complex were observed, whereas at high concentration the complex forms crystals and densely packed one‐dimensional structures. In STM topographies, the dimensions of assemblies of 1 found on the surface are consistent with dimensions obtained from X‐ray crystallography, which indicates the strong similarities between the crystal form and surface assembled states. Double chains are attributed to hydrogen...
Scanning tunneling microscopy images of alkane derivatives on graphite: role of electronic effects
2008
Scanning tunneling microscopy (STM) images of self-assembled monolayers of close-packed alkane chains on highly oriented pyrolitic graphite often display an alternating bright and dark spot pattern. Classical simulations suggest that a tilt of the alkane backbone is unstable and, therefore, unlikely to account for the contrast variation. First principles calculations based on density functional theory show that an electronic effect can explain the observed alternation. Furthermore, the asymmetric spot pattern associated with the minimum energy alignment is modulated depending on the registry of the alkane adsorbate relative to the graphite surface, explaining the characteristic moiré pattern that is often observed in STM images with close packed alkyl assemblies.
The Journal of Physical Chemistry C, 2008
Scanning tunneling microscopy (STM) and orbital-mediated tunneling spectroscopy (OMTS) are reported for N,N′-dioctyl-1,8:4,5-naphthalenediimide (diimide) adsorbed on highly ordered pyrolytic graphite (HOPG). The diimide forms well ordered monolayers either at the interface between HOPG and several phenylalkanes, or at the HOPG-air or HOPG-vacuum interface when adsorbed from toluene. Planar adsorption of the diimide ring on HOPG is observed. Hydrogen bonding, O and N interaction with HOPG, and π-π interactions appear to be the primary drivers for determining the monolayer structure which is stable and independent of the adsorption method. This is an unusual example since most alkane-substituted systems studied to date rely on alkane chain interactions (with HOPG and interdigitation) to drive the adsorbate structure on graphite. The observed unit cell has a) 2.0 (0.2 nm, b) 1.95 (0.2 nm, R) 67 (2°. The STM imaging is highly bias dependent and appears to be controlled (in the (2 V bias region) by an unoccupied orbital. Orbitalmediated tunneling spectra reveal a single strong electron affinity band near 3.5 eV below the vacuum level.
The Journal of Physical Chemistry C, 2008
Scanning tunneling microscopy (STM) and scanning force microscopy (SFM) have been used to study ultrathin films of a kind of nanographene, hexa(p-n-dodecylphenyl)hexabenzocoronene (HBC-PhC 12 ), on a highly oriented pyrolitic graphite (HOPG) surface. An electrical field, applied parallel to the substrate surface during adsorption from solution and subsequent drying, has been found to align columns of HBC-PhC 12 molecules with their long axes perpendicular to the field direction, independently from the HOPG lattice orientation underneath. The molecules, under field influence, adopt a tilted edge-on arrangement on the HOPG surface. On the contrary, the corresponding drop-cast films, dried in the absence of an electrical field, shows a faceon arrangement of the extended aromatic π-system of the HBC-PhC 12 discs, and no columnar structures ordered parallel to the graphite surface are recognized. Formation of unidirectionally aligned columns of HBC-PhC 12 molecules is, therefore, related to the influence of the electrical field during self-assembly of HBC-PhC 12 molecules on top of the conducting substrate. The electrical field competes favorably with the strong intermolecular interactions between HOPG and HBC, avoiding the epitaxial growth of thin films with the molecules in face-to-face arrangements parallel to the substrate. Our results constitute an important step toward control of the order and arrangement of functional conjugated molecules in ultrathin layers using electrical fields.
Photochemistry and Photobiology, 2007
The chlorosomal light-harvesting antennae of green phototrophic bacteria consist of large supramolecular aggregates of bacteriochlorophyll c (BChl c). The supramolecular structure of (3 1 -R/S)-BChl c on highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS 2 ) has been investigated by scanning tunneling microscopy (STM). On MoS 2 , we observed single BChl c molecules, dimers or tetramers, depending on the polarity of the solvent. On HOPG, we observed extensive selfassembly of the dimers and tetramers. We propose C؍O · · · H-O · · · Mg bonding networks for the observed dimer chains, in agreement with former ultraviolet-visible and infrared spectroscopic work. The BChl c moieties in the tetramers are probably linked by four C؍O · · · H-O hydrogen bonds to form a circle and further stabilized by Mg · · · O-H bondings to underlying BChl c layers. The tetramers form highly ordered, distinct chains and extended two-dimensional networks. We investigated semisynthetic chlorins for comparison by STM but observed that only BChl c self-assembles to well-structured large aggregates on HOPG. The results on the synthetic chlorins support our structure proposition.
Keywords: C–C coupling / Monolayers / Star-shaped compounds / Self-assembly / Scanning probe microscopy Flexible and straightforward syntheses of a series of D 3h-or C 3h-symmetrical star-shaped compounds with pyridine end groups are reported. In all cases, the acid-mediated cyclocon-densations of the corresponding aryl methyl ketone provided the central benzene ring. For the preceding preparation of the functionalized compound arms, Suzuki couplings were applied. The crucial introduction of the pyridine C-2 and C-6 substituents occurred by Fe(acac) 3-catalyzed alkylations (acac = acetylacetonate). The preparation of the C 3-symmetrical compound involved an alternating sequence of haloge
Self-assembly of long chain alkanes and their derivatives on graphite
The Journal of Chemical Physics, 2008
We combine scanning tunneling microscopy ͑STM͒ measurements with ab initio calculations to study the self-assembly of long chain alkanes and related alcohol and carboxylic acid molecules on graphite. For each system, we identify the optimum adsorption geometry and explain the energetic origin of the domain formation observed in the STM images. Our results for the hierarchy of adsorbate-adsorbate and adsorbate-substrate interactions provide a quantitative basis to understand the ordering of long chain alkanes in self-assembled monolayers and ways to modify it using alcohol and acid functional groups.
Applied Surface Science, 2020
We report on the scanning tunneling microscopy and small-wide angle X-ray scattering and diffraction of four linear and rigid π-conjugated p-phenyleneethynylene (PPE) oligomers. The four compounds possess two dodecanoxy side chains on the central PPE moiety, differ in conjugated length (3 and 5 phenyleneethynylene moieties) and are benzyl, Bz3PEBz, Bz5PEBz, or carboxylic acid, Ac3PEAc, Ac5PEAc, end-capped. We found that in the benzylbenzoate terminated oligomers, a staggered arrangement of molecules is obtained endorsed by the π-π interaction between the benzyls. In contrast, for the carboxylic acid terminated oligomers, a rather linear type arrangement is promoted by the hydrogen bond created between the carboxylic acid groups. In general, all of the molecules form a lamellar like pattern adopting face-on arrangements, where the conjugated backbones are flatlying on the HOPG surface. The lamella length corresponds to the oligomer conjugation length, while within the lamellae, the calculated distances correspond to the spacing between conjugated backbones with an average value of 2.06 nm, consistent with that found by XRD, SAXS and DFT/def-SVP for the oligomers that self-assemble with the lateral alkyl chains interdigitated. The lack of more dodecanoxy side chains on the rest of the pheneyleneethynylene moieties gives rise to mesoporous type self-assembled monolayers on HOPG.
Journal of Nanoscience and Nanotechnology, 2013
Two-dimensional self-assembly of dendritic amphiphilic molecule with ferroncenyl subsitutuents (2,3,4-tri-(11-ferroncenyl)undecyloxybenzoic acid, Fc 3 COOH) on highly oriented pyrolytic graphite surface was investigated by scanning tunneling microscopy at the liquid/solid interface. Fc 3 COOH molecule formed an ordered molecular nanostructure-an alternating big/small bright dots pattern on the graphite surface extended to several hundred nanometers. On the basis of the simulation and combined with our STM results, it is concluded that the molecular adsorption conformation has an appreciable effect on the interactions of molecule-molecule and molecule-substrate. The-interactions between ferrocene groups together with the van der Waals interactions between alkyl chains direct the stacking behavior of Fc 3 COOH molecules. Due to the steric constraints, no hydrogen bonding between the carboxyl groups was formed during the self-assembly.
The Journal of Physical Chemistry B, 2005
Self-assembled monolayers of chrysene and indene on graphite have been observed and characterized individually with scanning tunneling microscopy (STM) at 80 K under low-temperature, ultrahigh vacuum conditions. These molecules are small, polycyclic aromatic hydrocarbons (PAHs) containing no alkyl chains or functional groups that are known to promote two-dimensional self-assembly. Energy minimization and molecular dynamics simulations performed for small groups of the molecules physisorbed on graphite provide insight into the monolayer structure and forces that drive the self-assembly. The adsorption energy for a single chrysene molecule on a model graphite substrate is calculated to be 32 kcal/mol, while that for indene is 17 kcal/mol. Two distinct monolayer structures have been observed for chrysene, corresponding to highand low-density assemblies. High-resolution STM images taken of chrysene with different bias polarities reveal distinct nodal structure that is characteristic of the molecular electronic state(s) mediating the tunneling process. Density functional theory calculations are utilized in the assignment of the observed electronic states and possible tunneling mechanism. These results are discussed within the context of PAH and soot particle formation, because both chrysene and indene are known reaction products from the combustion of small hydrocarbons. They are also of fundamental interest in the fields of nanotechnology and molecular electronics.