Defect-Induced π-Magnetism into Non-Benzenoid Nanographenes

Abstract

The synthesis of nanographenes (NGs) with open-shell ground states have recently attained increasing attention in view of their interesting physicochemical properties and great prospects in manifold applications as suitable materials within the rising field of carbon-based magnetism. A potential route to induce magnetism in NGs is the introduction of structural defects, for instance non-benzenoid rings, in their honeycomb lattice. Here, we report the on-surface synthesis of three open-shell non-benzenoid NGs (A1, A2 and A3) on the Au(111) surface. A1 and A2 contain two five- and one seven-membered rings within their benzenoid backbone, while A3 incorporates one five-membered ring. Their structures and electronic properties have been investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy complemented with theoretical calculations. Our results provide access to open-shell NGs with a combination of non-benzenoid topologies previously precluded by conventional synthetic procedures.

Structural Expansion of Cyclohepta[def]fluorene towards Azulene‐Embedded Non‐Benzenoid Nanographenes

“…Finally, a comment regarding the systematic detachment of one methyl group per DMPA segment for all the observed species is appropriate. We hypothesized that the C−H activation of the methyl groups pointing upwards (see adsorption geometries in Figure 2) expected to undergo the oxidative ring closure, does not take place due to their large distance with respect to the catalyzing gold surface (see Figure S4 and S5 for the adsorption geometry of P after the cyclodehydrogenation corresponding to the reaction coordinates $${{d}_{1}}$$ , $${{d}_{2}}$$ , and $${{d}_{4}}$$ and species 3 with the pentagon rings formed at different positions) [5,8,45,46] …”

“…[1][2][3] Among them, the introduction of nonalternant units (i. e., azulene or heptalene) into non-benzenoid NGs could cause local changes in strain and molecular symmetry, thus significantly impacting their physicochemical properties. [4] Moreover, the topological transformation induced by these non-alternant moieties could also determine the electronic ground state of NGs, [5][6][7][8][9][10][11][12][13][14][15] affording the potential open-shell character and promising applications in organic spintronics. [16,17] As a representative example, pyrene (a) can be transformed into one of its non-alternant isomers, that is, cyclohepta[def]fluorene (b) (namely bis-periazulene), by replacing the inner naphthalene unit with azulene (Figure 1a), which is predicted to be an open-shell Kekulé structure with a low triplet ground state.…”

Steering Large Magnetic Exchange Coupling in Nanographenes near the Closed-Shell to Open-Shell Transition

“…Consequently, enormous efforts have been devoted to the synthesis of open-shell carbon nanostructures, with graphene nanoribbons and nanographenes (NGs) being outstanding examples. , The synthesis of open-shell carbon-based nanomaterials in solution is frequently hampered by their high reactivity that arises from unpaired electrons. In this regard, on-surface synthesis under ultra-high vacuum (UHV) conditions provides an attractive alternative to synthesize and stabilize reactive species on solid surfaces, while enabling their atomic-scale structural and electronic characterization using scanning probe microscopies. ,,− …”

A versatile platform for graphene nanoribbon synthesis, electronic decoupling, and spin polarized measurements

“…We see parallels to this conundrum in research following the pioneering studies on on-surface synthesis of graphene nanoribbons (GNRs) 1 and chemically tailored nano-graphenes. 2 For their synthesis, an overwhelming number of contributions have converged on the coinage metals gold [3][4][5][6][7][8][9][10][11][12][13][14][15] or copper. 2,[16][17][18][19] Although both provide simple preparation, gold is deemed favorable for tailored synthesis because it reliably facilitates polymerization directly at the halogenated carbon site.…”

“…For example, the on-surface reaction of 10,10 ′dibromo-9,9 ′ -bianthracene (DBBA) results in the growth of straight N = 7 armchair graphene nanoribbons (7-AGNRs) on Au(111), 1 whilst on Cu(111) partially chiral nanoribbons are formed. 17,20 However, with the emergence of magnetic signatures in carbon-based systems, [5][6][7]11,12,15,21 further investigation may depend on our ability to provide orbital-imaging, spin-polarization and decoupling from itinerant electrons that are hard to simultaneously satisfy for either substrate. When looking for model-systems of spin-polarization, we notice in cobalt nanoislands on copper 22,23 a similar monoculture with a heavy focus on this platform despite it being plagued by the rapid intermixing of Co and Cu at room temperature, 24 which precludes its use for thermally induced nano-graphene formation.…”