Synthesis of Dendronized Polymers on the Au(111) Surface

Abstract

Dendronized polymers (DPs) consist of a linear polymeric backbone with dendritic side chains. Fine-tuning of the functional groups in the side chains enriches the structural versatility of the DPs and imparts a variety of novel physical properties. Herein, the first on-surface synthesis of DPs is achieved via the postfunctionalization of polymers on Au(111), in which the surface-confinement-induced planar conformation and chiral configurations were unambiguously characterized. While the dendronized monomer was synthesized in situ on Au(111), the subsequent polymerization afforded only short, cross-linked DP chains owing to multiple side reactions. The postfunctionalization approach selectively produced brominated polyphenylene backbone moieties by the deiodination polymerization of 4-bromo-4″iodo-5′-(4-iodophenyl)-1,1′:3′,1″-terphenyl on Au(111), which smoothly underwent divergent cross-coupling reactions with two different isocyanides to form two types of DPs as individual long chains.

Toward Molecular Fractals on Surfaces: Designing Covalent Structures with the Monte Carlo Simulation Method

“…Moreover, to create persistent fractal molecular structures, the covalent linkage of specially designed tectons has also been used, including dehydration reactions, polycondensation of boronic compounds, , Schiff-base reactions, thioether linkage, and multifold Suzuki coupling . Another useful approach to fabricate covalent polymeric structures on surfaces has been the Ullmann coupling, which involves halogenated aromatics and catalytically active metal substrates and enables the synthesis of molecular constructs such as wires, − nanoribbons, − chiral dimers, cyclic oligomers, , networks, − and others . In this heterogeneous catalytic reaction, aryl halides split off halogen atoms upon adsorption on coinage metals such as copper, silver, and gold and further recombine to form covalent polymeric structures cemented by carbon–carbon bonds.…”

“…25 Another useful approach to fabricate covalent polymeric structures on surfaces has been the Ullmann coupling, which involves halogenated aromatics and catalytically active metal substrates and enables the synthesis of molecular constructs such as wires, 26−28 nanoribbons, 28−30 chiral dimers, 31 cyclic oligomers, 32,33 networks, 34−37 and others. 38 In this heterogeneous catalytic reaction, aryl halides split off halogen atoms upon adsorption on coinage metals such as copper, silver, and gold and further recombine to form covalent polymeric structures cemented by carbon− carbon bonds.…”

On-Surface Cross-Coupling Reactions

“…Using divergent cross-coupling, Li et al further developed the postfunctionalization of a small molecule and a linear polymer on Au(111), achieving the precise construction of planar dendrimers (Figure 6b) and dendronized polymers with a uniform conformation and configuration (Figure 6c). 65 Notably, divergent cross-couplings have also been applied to the postfunctionalization of supramolecular polymers, in which the chiral assembly of supramolecular polymers controls the enantioselectivity of divergent cross-coupling (Figure 6d). 63 This finding provides new insight for exploring enantioselective covalent reactions on surfaces, which can be used to synthesize chiral one-or two-dimensional carbon nanosystems with unique electronic properties.…”

“…Exogenous Pd atoms are critical for reducing the reaction barrier of debromination and thereby altering reaction kinetics to inhibit the homocoupling of aryl bromides. Using divergent cross-coupling, Li et al further developed the postfunctionalization of a small molecule and a linear polymer on Au(111), achieving the precise construction of planar dendrimers (Figure b) and dendronized polymers with a uniform conformation and configuration (Figure c) . Notably, divergent cross-couplings have also been applied to the postfunctionalization of supramolecular polymers, in which the chiral assembly of supramolecular polymers controls the enantioselectivity of divergent cross-coupling (Figure d) .…”

“…(c) On-surface synthesis of dendronized polymers via divergent cross-coupling. Reproduced with permission from ref . Copyright 2022 American Chemical Society.…”