On‐Surface Synthesis of Giant Conjugated Macrocycles

Abstract

We have achieved an on-surface synthesis of giant conjugated macrocycles having a diameter of % 7 nm and consisting of up to 30 subunits. The synthesis started with a debrominative coupling of the molecular precursors on a hot Ag(111) surface, leading to the formation of arched oligomeric chains and macrocycles. These products were revealed by scanning tunneling microscopy in combination with density functional theory to be covalent oligomers. These intermediates also display C-Ag organometallic bonds between parallel molecular subunits due to site-selective debromination and the asymmetric molecular conformation. Subsequent cyclodehydrogenation at higher temperatures steered the final conjugation of the macrocycles. Our findings provide a novel design strategy toward p-conjugated macrocycles and open up new opportunities for the precise synthesis of organic nanostructures.

Theoretical Modeling of the Metal‐Organic Precursors of Anthracene‐Based Covalent Networks on Surfaces

“…To date, numerous experimental studies of the Ullmann reaction have been performed in which such molecules as terphenyls, [9,10] polyaromatic hydrocarbons (PAHs), [11–14] porphyrins [15,16] and others [17,18] with differently introduced halogen atoms were used. Those studies demonstrated the possibility of creation of covalent polymers with diverse architectures, including macrocycles, [10,19] chains, [9,17,20] strands, [21] nanoribbons, [22,23] and networks [24,25] …”

Influence of Molecular Configurations on the Desulfonylation Reactions on Metal Surfaces

“…In recent decades, on-surface synthesis has received considerable attention because atomically defined and versatile low-dimensional nanostructures can be fabricated under ultrahigh vacuum. − In 2007, Grill et al reported the covalent bonding of bromo-substituted porphyrin through on-surface dehalogenative homocoupling on a coinage substrate . Since then, a wide range of surface-confined reactions have been investigated, including Ullmann-type reactions, − homocoupling of terminal alkynes, − decarboxylative polymerization, − click reactions, , imine formation, − Wurtz reaction, Bergman cyclization, − dehydrogenative homocoupling, − and more. − By the rational design of precursor molecules, atomically precise carbon-based nanomaterials, such as graphene nanoribbons, − polycyclic aromatic hydrocarbons, − 2D covalent organic frameworks, − and others, − have been successfully prepared on surfaces. In particular, the polymerization reaction of inert regular alkanes can be achieved via C–H bond activation on either an anisotropic Au(110) surface or along the step edge of a copper surface under mild conditions. − …”

High-Yield Production of Quantum Corrals in a Surface Reconstruction Pattern

“…On-surface chemical reactions , have recently developed into a promising way to prepare the otherwise inaccessible architectures with desired geometry as impressively exampled by the synthesis of graphene nanoribbons with atomically precise edges and well-defined width. , However, thermally activated on-surface reactions always lead to high defect density, small domain size, and limited regioselectivity. , For covalently linked organic nanopores and cycles, both entropy and in-plane strain effects coupled with competitive reaction pathways result in an ultralow yield and unwanted byproducts. , Long-range ordered two-dimensional (2D) nanoporous polymers in mesoscale lateral extension have been realized through topochemical photopolymerization, , but the number of known monomers with reactive packing is very limited. − Moreover, the realization of QCs in organic nanocavities on the noble metal surface requires that the pore size should be comparable to the Fermi wavelength of 2D electron gas. , These stringent requirements give rise to few experimental realizations of stable QCs in organic frameworks. − …”

“…20,21 For covalently linked organic nanopores and cycles, both entropy and in-plane strain effects coupled with competitive reaction pathways result in an ultralow yield and unwanted byproducts. 22,23 Long-range ordered two-dimensional (2D) nanoporous polymers in mesoscale lateral extension have been realized through topochemical photopolymerization, 24,25 but the number of known monomers with reactive packing is very limited. 26−28 Moreover, the realization of QCs in organic nanocavities on the noble metal surface requires that the pore size should be comparable to the Fermi wavelength of 2D electron gas.…”