Observation of the Magnetic Ground State of the Two Smallest Triangular Nanographenes

Turco, Elia; Bernhardt, Annika; Krane, Nils; Valenta, Leoš; Fasel, Román; Jurı́ček, Michal; Ruffieux, Pascal

doi:10.1021/jacsau.2c00666

Cited by 38 publications

(31 citation statements)

References 69 publications

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“…Triangulene (TRI) is the smallest PAH diradical with a triplet ground state . Analogously, monoradicals such as nitrogen-doped triangulene (TRI(N)), boron-doped triangulene (TRI(B)), TAM, TOT, and phenalenyl (PLY) have also been synthesized either in solution or on the surface (Figure ).…”

Section: Resultsmentioning

confidence: 99%

“…Analogously, monoradicals such as nitrogen-doped triangulene (TRI(N)), boron-doped triangulene (TRI(B)), TAM, TOT, and phenalenyl (PLY) have also been synthesized either in solution or on the surface (Figure ). ,,,,− Among them, TRI, TAM, TOT, and PLY have D 3 h symmetry, while TRI(N) and TRI(B) exhibit lower symmetry of C 2 v due to Jahn–Teller distortion . The C 2 v configuration is more energetically favorable than the D 3 h configuration by 5.63 and 5.58 kJ/mol, resulting in the distorted symmetry for TRI(N) and TRI(B) (Table S1).…”

Section: Resultsmentioning

confidence: 99%

“…Triangulene (TRI) is the smallest PAH diradical with a triplet ground state. 46 Analogously, monoradicals such as nitrogendoped triangulene (TRI(N)), boron-doped triangulene (TRI-(B)), TAM, TOT, and phenalenyl (PLY) have also been synthesized either in solution or on the surface (Figure 1). 6,9,18,20,46−49 Among them, TRI, TAM, TOT, and PLY have D 3h symmetry, 6 while TRI(N) and TRI(B) exhibit lower symmetry of C 2v due to Jahn−Teller distortion.…”

Section: ■ Introductionmentioning

confidence: 99%

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Magnetic Coupling Control in Triangulene Dimers

Yu,

Heine

2023

J. Am. Chem. Soc.

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Metal-free magnetism remains an enigmatic field, offering prospects for unconventional magnetic and electronic devices. In the pursuit of such magnetism, triangulenes, endowed with inherent spin polarization, are promising candidates to serve as monomers to construct extended structures. However, controlling and enhancing the magnetic interactions between the monomers persist as a significant challenge in molecular spintronics, as so far only weak antiferromagnetic coupling through the linkage has been realized, hindering their room temperature utilization. Herein, we investigate 24 triangulene dimers using firstprinciples calculations and demonstrate their tunable magnetic coupling (J), achieving unprecedented strong J values of up to −144 meV in a non-Kekulédimer. We further establish a positive correlation between bandgap, electronic coupling, and antiferromagnetic interaction, thereby providing molecular-level insights into enhancing magnetic interactions. By twisting the molecular fragments, we demonstrate an effective and feasible approach to control both the sign and strength of J by tuning the balance between potential and kinetic exchanges. We discover that J can be substantially boosted at planar configurations up to −198 meV. We realize ferromagnetic coupling in nitrogen-doped triangulene dimers at both planar and largely twisted configurations, representing the first example of ferromagnetic triangulene dimers that cannot be predicted by the Ovchinnikov rule. This work thus provides a practical strategy for augmenting magnetic coupling and open up new avenues for metal-free ferromagnetism.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Magnetic Coupling Control in Triangulene Dimers

Yu,

Heine

2023

J. Am. Chem. Soc.

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“…[1,[7][8][9][10] Owing to their open-shell character, the solution synthesis of triangulenes is very challenging. [11][12][13] Lately, onsurface-synthesis (OSS) strategies [14,15] have demonstrated to be a viable route for the fabrication of atomically perfect triangulenes with increasing size [16][17][18][19][20] (some of these shown in Figure 1a). Interestingly, OSS can also produce more complex triangulene nanostructures, [21][22][23][24][25][26][27] with a variety of magnetic properties emerging from the exchange interaction between triangulene units.…”

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confidence: 99%

On‐Surface Synthesis and Characterization of a High‐Spin Aza‐[5]‐Triangulene

Vilas‐Varela,

Romero‐Lara,

Vegliante

et al. 2023

Angew Chem Int Ed

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Triangulenes are a class of open‐shell triangular graphene flakes with total spin increasing with their size. In the last years, on‐surface‐synthesis strategies have permitted fabricating and engineering triangulenes of various sizes and structures with atomic precision. However, direct proof of the increasing total spin with their size remains elusive. In this work, we report the combined in‐solution and on‐surface synthesis of a large nitrogen‐doped triangulene (aza‐[5]‐triangulene) on a Au(111) surface, and the detection of its high‐spin ground state. Bond‐resolved scanning tunneling microscopy images uncovered radical states distributed along the zigzag edges, which were detected as weak zero‐bias resonances in scanning tunneling spectra. These spectral features reveal the partial Kondo screening of a high‐spin state. Through a combination of several simulation tools, we find that the observed distribution of radical states is explained by a quintet ground state (S=2), instead of the quartet state (S=3/2) expected for the neutral species. This confirms that electron transfer to the metal substrate raises the spin of the ground state. We further provide a qualitative description of the change of (anti)aromaticity introduced by N‐substitution, and its role in the charge stabilization on a surface, resulting in an S=2 aza‐triangulene on Au(111).

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“…Triangulene is the most studied molecule displaying π-magnetism due to sublattice imbalance. , While solution-phase syntheses of kinetically stabilized derivatives were reported recently, , on-surface techniques have produced and characterized larger and smaller derivatives, − , dimers, trimers, and larger oligomers. , Inspired by how heteroatom doping enriches the chemistry and physical properties of nanographenes, we recently showed that the presence of a nitrogen atom in the carbon framework of triangulene, as in aza-triangulene ( 1 , Scheme ), triggered charge transfer in opposite directions on Au(111) and Ag(111) . Because the redox potentials of 1 lie in the narrow window between the work functions of these substrates, an oxidized cationic species 1 + with open-shell S = 1 character was observed on Au(111) while a reduced closed-shell anionic species 1 – was observed on Ag(111) .…”

mentioning

confidence: 99%

Emergence of π-Magnetism in Fused Aza-Triangulenes: Symmetry and Charge Transfer Effects

Calupitan,

Berdonces-Layunta,

Aguilar-Galindo

et al. 2023

Nano Lett.

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On-surface synthesis has paved the way toward the fabrication and characterization of conjugated carbon-based molecular materials that exhibit π-magnetism such as triangulenes. Azatriangulene, a nitrogen-substituted derivative, was recently shown to display rich on-surface chemistry, offering an ideal platform to investigate structure−property relations regarding spin-selective charge transfer and magnetic fingerprints. Herein, we study electronic changes upon fusion of single molecules into larger dimeric derivatives. We show that the closed-shell structure of aza-triangulene on Ag(111) leads to closed-shell dimers covalently coupled through sterically accessible carbon atoms. Meanwhile, its open-shell structure on Au(111) leads to coupling via atoms displaying a high spin density, resulting in symmetric or asymmetric products. Interestingly, whereas all dimers on Au(111) exhibit similar charge transfer properties, only asymmetric ones show magnetic fingerprints due to spin-selective charge transfer. These results expose clear relationships among molecular symmetry, charge transfer, and spin states of π-conjugated carbon-based nanostructures.

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Observation of the Magnetic Ground State of the Two Smallest Triangular Nanographenes

Cited by 38 publications

References 69 publications

Magnetic Coupling Control in Triangulene Dimers

Magnetic Coupling Control in Triangulene Dimers

On‐Surface Synthesis and Characterization of a High‐Spin Aza‐[5]‐Triangulene

Emergence of π-Magnetism in Fused Aza-Triangulenes: Symmetry and Charge Transfer Effects

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