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![STM image exhibiting multidomains for DBC films. (a) The film was prepared when the shear was ∼ 30 ° off from [01 j 0] of HOPG. (b) Coexistence of edge-on and face-on orientations of DBC near location c in Figure 2. Conditions: E bias , - 0.80 V; I tunneling , 60 pA. Image size: (a) 350 × 350 nm 2 , 50 × 50 nm 2 (inset), (b) 40 × 40 nm 2 .](profile/Kamalkishore-Pati/publication/249916834/figure/fig2/AS:298292194889729@1448129809176/STM-image-exhibiting-multidomains-for-DBC-films-a-The-film-was-prepared-when-the-shear.png)
STM image exhibiting multidomains for DBC films. (a) The film was prepared when the shear was ∼ 30 ° off from [01 j 0] of HOPG. (b) Coexistence of edge-on and face-on orientations of DBC near location c in Figure 2. Conditions: E bias , - 0.80 V; I tunneling , 60 pA. Image size: (a) 350 × 350 nm 2 , 50 × 50 nm 2 (inset), (b) 40 × 40 nm 2 .
Source publication
The control of spatial arrangements of molecular building blocks on surface opens the foundational step of the bottom-up approach toward future nanotechnologies. Contemporarily, the domain size of monolayers exhibiting crystallinity falls in the submicron scale. Developed herein is a method that allows the alignment of polyaromatics with one-single...
Citations
Double-stranded polymeric ladderphane 1 using HBC as linkers and the single-stranded comblike polynorbornene 2 with HBC pendants are synthesized by the ring-opening metathesis polymerization using the first-generation Grubbs catalyst. The photophysical properties of these HBC-incorporated polymers indicate significant interactions between adjacent polynuclear aromatic chromophores which are comparable with those of aggregated forms of the HBC cores. No liquid crystal properties, however, are observed in these polymers. The STM images of 1 and 2 demonstrate the unique properties of polynorbornene derivatives having N-aryl-5,6-endopyrrolidene pendants or linkers where the polymers are self-assembled to form ordered two-dimensional arrays on the HOPG surface.
In this scanning-tunneling-microscopy/spectroscopy study (STM/STS), samples of isolated and close-packed dibenzo[g,p]chrysene (DBC), a nonplanar polyaromatic compound, are used as model systems to demonstrate the effect of intermolecular interactions on the electronic structures. For dropcast films, DBC molecules adopt an edge-on orientation in a close-packed structure on graphite. Isolated DBC molecules are prepared on graphite from a DBC-coated STM tip by a ca. 7 V/10 μs pulse. STS spectra for both isolated- and close-packed DBC molecules exhibit diode-like I-V curves in which the latter shows a turn-on voltage (0.47 V) smaller than that of the former (0.91 V). The diode-like behaviors are attributed to the more-facile tunneling of electrons through the HOMO of DBC than through the LUMO. The reduced turn-on voltage for the films is ascribed to the diminished HOMO-LUMO gap based on the results of DFT (density functional theory) simulations for the energy-level couplings of π-stacked DBC molecules.
