Where do the counterions go? Tip-induced dissociation of self-assembled triazatriangulenium-based molecules on Au(111)

Snegir, Sergii; Dappe, Yannick J.; Sysoiev, Dmytro; Pluchery, Olivier; Huhn, Thomas; Scheer, Elke

doi:10.1039/d1cp00221j

Cited by 7 publications

(21 citation statements)

References 33 publications

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“…57 The main objective is to simulate the experimental molecular gating by changing the charge state of the molecule in a self-consistent manner, and to deduce the corresponding electronic transmissions. 58–60 The molecular levels are shifted due to the gating and the resonance is obtained when a molecular level crosses the Fermi level. In Fig.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical gating for single-molecule electronics with hybrid Au|graphene contacts

Tao

Zhang

Vezzoli

et al. 2022

Phys. Chem. Chem. Phys.

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Section: Resultsmentioning

confidence: 99%

Electrochemical gating for single-molecule electronics with hybrid Au|graphene contacts

Tao

Zhang

Vezzoli

et al. 2022

Phys. Chem. Chem. Phys.

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“…Loss of counterions from an adsorbed monolayer has previously been observed for charged SAMs comprising triazatriangulenium (TATA)-based components, in independent studies using both XPS 7 and scanning tunnelling microscopy (STM). 53 It was suggested that counterion loss would imply a significant charge transfer to the substrate, 7 and that this may be favored by the electric field generated at an STM tip. 53 Computational studies further revealed that while a TATA + -BF4ion pair is stabilized by adsorption on a gold surface, its cohesive energy is reduced by addition of an electron to the system.…”

Section: Discussionmentioning

confidence: 99%

“…53 It was suggested that counterion loss would imply a significant charge transfer to the substrate, 7 and that this may be favored by the electric field generated at an STM tip. 53 Computational studies further revealed that while a TATA + -BF4ion pair is stabilized by adsorption on a gold surface, its cohesive energy is reduced by addition of an electron to the system. 53 It remains unclear whether counterion loss in TATA-based SAMs may occur prior to XPS or STM studies, and if so, what the mechanism of surface reduction might be.…”

Section: Discussionmentioning

confidence: 99%

“…53 Computational studies further revealed that while a TATA + -BF4ion pair is stabilized by adsorption on a gold surface, its cohesive energy is reduced by addition of an electron to the system. 53 It remains unclear whether counterion loss in TATA-based SAMs may occur prior to XPS or STM studies, and if so, what the mechanism of surface reduction might be. We note that the intercomponent spacing in TATA-based SAMs, formed from neutral or charged precursors, is predominately controlled by the length of alkyl substituents.…”

Section: Discussionmentioning

confidence: 99%

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Mixed monolayers formed from methyldisulfide-functionalized metal bis(terpyridine) complexes

Trang

Saal

Inkpen

2022

Preprint

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Multicomponent self-assembled monolayers (SAMs) often suffer from segregation of like components into nanoscale domains. One strategy to form perfectly mixed SAMs is to use a modular series of molecules with similar structures and dimensions, ensuring comparable formation kinetics as well as surface and intermolecular interactions. To help evaluate this concept, we prepared a new family of methyldisulfide-functionalized metal bis(terpyridine) complexes, [M(tpySSMe)2](PF6)2 (M = Fe, Co, Zn), and characterized their single- and multi-component SAMs on gold surfaces. We find these complexes are air-stable in solution for >7 d, in stark contrast to their thiol-functionalized analogues, [M(tpySH)2](PF6)2 (MSH, M = Fe, Co), which decompose in <1 d. Though CoSH has been previously reported, we explicitly detail its synthesis and characterization here for the first time. Solution and surface voltammetry experiments show these complexes can indeed form SAMs with compositions representative of their assembly solutions, a prerequisite for perfect mixing at the molecular scale. However, we find MSS and CoSS SAMs generally exhibit remarkably low saturation surface coverages. This observation agrees with earlier SAM studies involving different polypyridyl-based metal complexes, and is typically attributed to repulsive Coulomb interactions between charged complexes on the surface. Despite their apparent loose packing, we show that purportedly vacant surface sites in MSS SAMs are not readily accessible for coordination by uncharged thiols in solution. X-ray photoelectron spectroscopy studies of CoSS SAMs further reveal clear S 2p (primarily of thiolate character) and N 1s features, but show no F 1s signal attributable to PF6− counterions (either due to their absence or the low surface coverage of MSS). This study raises important new questions regarding the assembly mechanism and nanoscale structure of these and other, structurally-related, charged SAMs, also serving to highlight key challenges in the design and characterization of emerging multi-component monolayer assemblies.

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“…Neither X-ray photoelectron spectroscopy (XPS) nor electrochemical STM in a HClO 4 electrolyte could detect BF 4 – moieties on the surface . Instead, the authors attribute this behavior to a strong interaction of the monolayer with the Au(111) substrate, leading to a screening of the positive charge of the cation and removal of the corresponding anion after adsorption of the monolayer. ,, Recently, we succeeded in clarifying the whereabouts of the BF 4 – anion on Au(111) by heat-aided deposition of TATA-BF 4 from 1,2,4-trichlorobenzene solvent . The counterions could be localized only under specific tunneling conditions.…”

Section: Introductionmentioning

confidence: 99%

Nonuniform STM Contrast of Self-Assembled Tri-n-octyl-triazatriangulenium Tetrafluoroborate on HOPG

Snegir,

Dappe,

Sysoiev

et al. 2023

ACS Omega

Self Cite

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We have assembled 4,8,12-tri-n-octyl-4,8,12-triazatrianguleniumtetrafluoroborate (TATA-BF4) on highly oriented pyrolytic graphite (HOPG) and have studied the structure and tunneling properties of this self-assembled monolayer (SAM) using scanning tunneling microscopy (STM) under ambient conditions. We show that the triazatriangulenium cations TATA+ form hexagonally packed structures driven by the interaction between the aromatic core and the HOPG lattice, as evidenced by density functional theory (DFT) modeling. According to the DFT results, the three alkyl chains of the platform tend to follow the main crystallographic directions of HOPG, leading to a different STM appearance. The STM contrast of the SAM shows that the monolayer is formed by two types of species, namely, TATA+ with BF4 – counterions on top and without them. The cationic TATA+ platform gives rise to a seemingly higher appearance than neutral TATA-BF4, in contrast to observations made on metallic substrates. The variation of the STM tunneling parameters does not change the relative difference of contrast, revealing the stability of both species on HOPG. DFT calculations show that TATA-BF4 on HOPG has sufficient binding energy to resist dissociation into TATA+ and BF4 –, which might occur under the action of the electric field in the tunneling gap during STM scanning.

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Where do the counterions go? Tip-induced dissociation of self-assembled triazatriangulenium-based molecules on Au(111)

Abstract: Chemical coupling of functional molecules on top of so-called platform molecules allows the formation of functional self-assembled monolayers (SAMs). An often-used example of such a platform is triazatriangulenium (TATA), which...

Cited by 7 publications

References 33 publications

Electrochemical gating for single-molecule electronics with hybrid Au|graphene contacts

Electrochemical gating for single-molecule electronics with hybrid Au|graphene contacts

Mixed monolayers formed from methyldisulfide-functionalized metal bis(terpyridine) complexes

Nonuniform STM Contrast of Self-Assembled Tri-n-octyl-triazatriangulenium Tetrafluoroborate on HOPG

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