Abstract:On-surface synthesis is a unique tool for growing low-dimensional carbon nanomaterials with precise structural control down to the atomic level. This novel approach relies on carefully designed precursor molecules, which are deposited on suitable substrates and activated to ultimately form the desired nanostructures. One of the most applied reactions to covalently interlink molecular precursors is dehalogenative aryl-aryl coupling. Despite the versatility of this approach, many unsuccessful attempts are also k… Show more
“…Furthermore, under UHV conditions, hydrogen is the predominant compound in the rest gas of the vacuum chamber, and hydrogen atoms may also be produced by surface-promoted dissociation after cleavage of the ethano protecting groups. Similar passivation of reactive molecules or GNRs on surfaces has been reported before 40 , 43 , 64 – 66 .…”
Heteroatom substitution in acenes allows tailoring of their remarkable electronic properties, expected to include spin-polarization and magnetism for larger members of the acene family. Here, we present a strategy for the on-surface synthesis of three undecacene analogs substituted with four nitrogen atoms on an Au(111) substrate, by employing specifically designed diethano-bridged precursors. A similarly designed precursor is used to synthesize the pristine undecacene molecule. By comparing experimental features of scanning probe microscopy with ab initio simulations, we demonstrate that the ground state of the synthesized tetraazaundecacene has considerable open-shell character on Au(111). Additionally, we demonstrate that the electronegative nitrogen atoms induce a considerable shift in energy level alignment compared to the pristine undecacene, and that the introduction of hydro-aza groups causes local anti-aromaticity in the synthesized compounds. Our work provides access to the precise fabrication of nitrogen-substituted acenes and their analogs, potential building-blocks of organic electronics and spintronics, and a rich playground to explore π-electron correlation.
“…Furthermore, under UHV conditions, hydrogen is the predominant compound in the rest gas of the vacuum chamber, and hydrogen atoms may also be produced by surface-promoted dissociation after cleavage of the ethano protecting groups. Similar passivation of reactive molecules or GNRs on surfaces has been reported before 40 , 43 , 64 – 66 .…”
Heteroatom substitution in acenes allows tailoring of their remarkable electronic properties, expected to include spin-polarization and magnetism for larger members of the acene family. Here, we present a strategy for the on-surface synthesis of three undecacene analogs substituted with four nitrogen atoms on an Au(111) substrate, by employing specifically designed diethano-bridged precursors. A similarly designed precursor is used to synthesize the pristine undecacene molecule. By comparing experimental features of scanning probe microscopy with ab initio simulations, we demonstrate that the ground state of the synthesized tetraazaundecacene has considerable open-shell character on Au(111). Additionally, we demonstrate that the electronegative nitrogen atoms induce a considerable shift in energy level alignment compared to the pristine undecacene, and that the introduction of hydro-aza groups causes local anti-aromaticity in the synthesized compounds. Our work provides access to the precise fabrication of nitrogen-substituted acenes and their analogs, potential building-blocks of organic electronics and spintronics, and a rich playground to explore π-electron correlation.
“…(B, C) STM images of an Au(111) surface after deposition of 1 and 6 and annealing to 270 °C, with labeled alternation of building blocks (B) and IF linkers (L). (D) Constant‐height frequency‐shift nc‐AFM image of a copolymer segment, revealing the chemical structure reported in E. reproduced with permission 77 . Copyright 2019, John Wiley and Sons…”
Section: Indenofluorene Polymersmentioning
confidence: 99%
“…In another study, bromoethylene functional groups located at the five‐membered ring apexes of an IF precursor afforded IF polymers that extended perpendicular to the long axis of their repeat units, with cumulene‐like bridges between them 76 . Finally, IF precursors were also used as linkers to overcome steric hindrance in aryl‐aryl homocoupling 77 . After an overview on all these results, we will discuss present challenges and future perspectives of IF polymers.…”
Section: Introductionmentioning
confidence: 99%
“…76 Finally, IF precursors were also used as linkers to overcome steric hindrance in aryl-aryl homocoupling. 77 After an overview on all these results, we will discuss present challenges and future perspectives of IF polymers.…”
Polycyclic hydrocarbons with nonzero radical character have attracted enormous interest as potential active media for organic electronics and spintronics. In this context, indenofluorenes are an intriguing class of formally antiaromatic, biradical materials with a radical character that depends on the connectivity of their six‐ and five‐membered rings. Synthesis of indenofluorene polymers and related compounds, first achieved in the early ‘90s with the production of ladder‐type chains, represents a major step toward incorporation of these systems into devices. However, solution‐based synthetic protocols require bulky protecting groups to stabilize the most reactive sites and, at the same time, to improve solubility and processability of such compounds. The preparation of various pristine – that is, unprotected—indenofluorene polymers has recently become possible via the on‐surface synthesis approach, where the resulting nanostructures are supported and efficiently stabilized by the underlying substrate in ultrahigh vacuum conditions. Here, an overview of these recent works is given, with a focus on synthetic challenges, structural details and electronic properties.
“…31 Only recently, the on-surface synthesis of several CLPs containing nonbenzenoid rings has been reported. [32][33][34][35][36][37][38] Nevertheless, systematic investigations of the structural and electronic properties resulting from selective incorporation of nonbenzenoid rings into CLPs are still lacking.…”
On-surface synthesis provides a powerful approach toward the fabrication of π-conjugated ladder polymers (CLPs). The synthesis of nonbenzenoid CLPs is achieved following two activation steps, including the formation of an intermediate 1D polymer.
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