Structural selection of graphene supramolecular assembly oriented by molecular conformation and alkyl chain

Abstract

Graphene molecules, hexafluorotribenzo[a,g,m]coronene with ncarbon alkyl chains (FTBC-Cn, n ‫؍‬ 4, 6, 8, 12) and Janus-type ''double-concave'' conformation, are used to fabricate self-assembly on highly oriented pyrolytic graphite surface. The structural dependence of the self-assemblies with molecular conformation and alkyl chain is investigated by scanning tunneling microscopy and density functional theory calculation. An interesting reverse face ''up-down'' way is observed in FTBC-C4 assembly due to the existence of hydrogen bonds. With the increase of the alkyl chain length and consequently stronger van der Waals interaction, the molecules no longer take alternating ''up-down'' orientation in their self-assembly and organize into various adlayers with lamellar, hexagonal honeycomb, and pseudohoneycomb structures based on the balance between intermolecular and molecule-substrate interactions. The results demonstrate that the featured ''double-concave'' molecules are available block for designing graphene nanopattern. From the results of scanning tunneling spectroscopy measurement, it is found that the electronic property of the featured graphene molecules is preserved when they are adsorbed on solid surface.graphene molecule ͉ Janus-type double-concave conformation ͉ scanning tunneling microscopy ͉ self-assembly A graphene molecules is composed of fused aromatic sets and is regarded as graphite subunit. After the success in theoretical prediction and experimental realization of graphene, graphene type molecules attract a great deal of interest (1-4). Their unique structures provide them promising potentials in micro/nano electronic devices (5-7). Continuous effort in chemical synthesis of graphene type molecules has produced various graphene molecules with the structures and properties beyond simple graphene. For example, polycyclic aromatic hydrocarbons (PAHs) compounds belong to a class of important functional graphene molecules (7,8). PAHs and their derivatives contain 2D subsections of graphene and show significant advantages, such as good solubility and ability to bear different chemical functionalities in their periphery with various electronic properties. These graphene molecules are promising candidates as building block for nanodevices through self-assembled architectures on 2D solid surfaces (9, 10).As a powerful tool for nanoscience and nanotechnology, scanning probe microscopy, in particular, scanning tunneling microscopy (STM) studies have produced images of the molecular self-assembly of graphene molecules at atomic/submolecular resolution, providing molecular understanding of intermolecular interactions and origin of their physical/chemical properties (11)(12)(13)(14). Because of their chemical structures, most of PAHs have a planar conformation and are inclined to form well-defined long-range self-assemblies on various substrates, such as gold and highly oriented pyrolytic graphite (HOPG). For examples, an alkyl-substituted PAH with D 2h symmetry and 78 carbon atoms in the aromatic core can se...

Structure and structural transition of chiral domains in oligo(p-phenylenevinylene) assembly investigated by scanning tunneling microscopy

“…With atomic resolution, scanning tunneling microscopy (STM) is powerful in surface chirality study (4)(5)(6)(7). From absolute chirality determination to chiral structure fabrication with chiral molecules or achiral molecules on a solid surface, a few results have been reported (8)(9)(10)(11)(12)(13). Xu et al directly observed the chirality of (R)-and (S)-2-phenylpropionamide molecules on Cu(111) in solution by using electrochemical STM (14).…”

Two-dimensional self-assemblies of telechelic organic compounds: structure and surface host–guest chemistry

“…In addition, two-dimensional crystallization energy resulting from van der Waals forces between long alkyl chains can induce full interdigitation of alkyl chains and leads to the densely packed lamellar structures on surfaces [18]. Owing to the inherent conformation flexibility of alkyl chains, the interesting structural evolution of functional molecule homologues decorated with alkyl chains with different lengths has been observed in a number of systems [13][14][15][16].…”

“…In the case of MPc/TCDB architectures, the calculated result shows that van der Waals forces are the main intermolecular interactions because of the rather weak interaction between a TCDB dimer and MPc (about 7.8 kcal mol −1 for CuPc/TCDB architectures). However, in the composite architecture F 16 CuPc/TCDB(II) structures (shown in figure 3a), two F 16 CuPc molecules are entrapped by each cavity of the TCDB nanoporous network. The electronegative characteristics of the fluorine groups in F 16 CuPc molecules lead to a higher dipole moment and induce the intermolecular mutual repulsion between two adjacent F 16 CuPc molecules in each cavity [60].…”

“…However, in the composite architecture F 16 CuPc/TCDB(II) structures (shown in figure 3a), two F 16 CuPc molecules are entrapped by each cavity of the TCDB nanoporous network. The electronegative characteristics of the fluorine groups in F 16 CuPc molecules lead to a higher dipole moment and induce the intermolecular mutual repulsion between two adjacent F 16 CuPc molecules in each cavity [60]. As a result, the central Pc-Pc distance between two F 16 CuPc molecules in a cavity varies from 1.5 to 1.7 nm and the cavities are expanded.…”

“…Non-covalent bond interactions, for instance van der Waals forces [16][17][18][19][20], hydrogen bonds [21][22][23][24], π -π stacking interactions [25,26], dipole-dipole interactions [27][28][29] and electrostatic interactions [30,31] between functional groups in organic molecules, play an important role in the self-assembly process. Long alkyl chains have been widely applied to immobilize organic molecules to obtain two-dimensional periodic arrangements on surfaces through van der Waals forces between alkyl chains and a substrate [16,17]. In addition, two-dimensional crystallization energy resulting from van der Waals forces between long alkyl chains can induce full interdigitation of alkyl chains and leads to the densely packed lamellar structures on surfaces [18].…”