Low-Dimensional Porous Carbon Networks Using Single-/Triple-Coupling Polycyclic Hydrocarbon Precursors

Abstract

Polycyclic hydrocarbons (PHs) share the same hexagonal structure of sp 2 carbons as graphene but possess an energy gap due to quantum confinement effect. PHs can be synthesized by a bottom-up strategy starting from small building blocks covalently bonded into large 2D organic sheets. Further investigation of the role of the covalent bonding/ coupling ways on their electronic properties is needed. Here, we demonstrate a surface-mediated synthesis of hexa-peri-hexabenzocoronene (HBC) and its extended HBC oligomers (dimers, trimers, and tetramers) via single-and triple-coupling ways and reveal the implication of different covalent bonding on their electronic properties. High-resolution low-temperature scanning tunneling microscopy and noncontact atomic force microscopy are employed to in situ determine the atomic structures of as-synthesized HBC oligomers. Scanning tunneling spectroscopy measurements show that the length extension of HBC oligomers narrows the energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Furthermore, the energy gaps of triple-coupling HBC oligomers are smaller and decrease more significantly than that of the single-coupling ones. We hypothesize that the triple coupling promotes a more effective delocalization of π-electrons than the single coupling, according to density functional theory calculations. We also demonstrate that the HBC oligomers can further extend across the substrate steps to achieve conjugated polymers and largearea porous carbon networks.

Structural Transformation of Azonia[5]helicene Photoproduct via Reaction Field Function of Layered Inorganic Material

“…This research area is called “on surface synthesis.” Chemical reactions have been carried out on flat metallic surfaces, such as Au (111) and Cu (001). The reaction products can be observed directly by imaging the molecular structure using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). − This direct observation is one of the clear advantages of this field, but the interesting point of this system is the shape of the reaction field. Interactions between flat metallic surfaces and organic molecules accelerate chemical reactions and sometimes transform the molecular structure of the final product into a more planar structure. ,− Flat reaction fields have unique potential in organic chemistry because they can exert novel steric effects on molecules that do not appear in solution systems.…”

Topology selectivity of a conformationally flexible precursor through selenium doping

“…Among diverse on-surface reactions, the Ullmann coupling has been a milestone and one of the most explored reactions in on-surface science, in which precursors undergo dehalogenation, organometallic (OM), and covalent interlinking effectively and efficiently [9][10][11][12] . To date, most on-surface synthesis explorations have been primarily concentrated in conformationally rigid precursors [13][14][15][16][17][18] , with limited attention paid to conformationally flexible precursors.…”