Toward Two-Dimensional Tessellation through Halogen Bonding between Molecules and On-Surface-Synthesized Covalent Multimers

Abstract

The ability to engineer sophisticated two-dimensional tessellation organic nanoarchitectures based on triangular molecules and on-surface-synthesized covalent multimers is investigated using scanning tunneling microscopy. 1,3,5-Tris(3,5-dibromophenyl)benzene molecules are deposited on high-temperature Au(111) surfaces to trigger Ullmann coupling. The self-assembly into a semi-regular rhombitrihexagonal tiling superstructure not only depends on the synthesis of the required covalent building blocks but also depends on their ratio. The organic tessellation nanoarchitecture is achieved when the molecules are deposited on a Au(111) surface at 145 °C. This halogen-bonded structure is composed of triangular domains of intact molecules separated by rectangular rows of covalent dimers. The nearly hexagonal vertices are composed of covalent multimers. The experimental observations reveal that the perfect semi-regular rhombitrihexagonal tiling cannot be engineered because it requires, in addition to the dimers and intact molecules, the synthesis of covalent hexagons. This building block is only observed above 165 °C and does not coexist with the other required organic buildings blocks.

On-Surface Molecular Recognition Driven by Chalcogen Bonding

“…The second aspect that drives flourishing interest for SBIs relies on the orbital mixing, described as n 2 (Y) → σ*­(E–X) donation involving nonbonding electrons of the electron-rich Y atom, and the antibonding σ E–X * on the E atom (with X being its covalent substituent). Within the category of SBIs, halogen bonding interactions − have demonstrated their efficacy in creating regular supramolecular networks on surfaces, , as revealed by scanning tunneling microscopy (STM) studies highlighting intermolecular Br···O, , Br···Br, , and Br···S halogen bonds (Figure d) governing the self-assembly. However, chalcogen bonding interactions (ChBIs) have not yet demonstrated comparable effectiveness on surfaces as they have in crystal engineering − for developing functional materials, such as supramolecular semiconductors. , Intermolecular Ch···N ChBs acting as the driving force for self-assembling chalcogenazole derivatives on surfaces, have only been theoretically explored in two recent studies. , To the best of our knowledge, the role of ChB interactions in driving self-assembly on surfaces remained largely underinvestigated experimentally when compared to hydrogen bonds, metal coordination bonds, and dipole–dipole interactions, with only two reports suggesting the presence of ChB interactions and other noncovalent contacts. , …”

“… 23 The second aspect that drives flourishing interest for SBIs relies on the orbital mixing, 24 described as n 2 (Y) → σ*(E–X) donation involving nonbonding electrons of the electron-rich Y atom, and the antibonding σ E–X * on the E atom (with X being its covalent substituent). Within the category of SBIs, halogen bonding interactions 25 − 29 have demonstrated their efficacy in creating regular supramolecular networks on surfaces, 30 , 31 as revealed by scanning tunneling microscopy (STM) studies highlighting intermolecular Br···O, 32 , 33 Br···Br, 34 , 35 and Br···S 36 halogen bonds ( Figure 1 d) governing the self-assembly. However, chalcogen bonding interactions (ChBIs) 37 have not yet demonstrated comparable effectiveness on surfaces as they have in crystal engineering 38 − 42 for developing functional materials, 43 such as supramolecular semiconductors.…”