Dodecacene Generated on Surface: Reopening of the Energy Gap

Eisenhut, Frank; Kühne, Tim; García, Francisco Martínez; Fernández, Saleta; Guitián, Enrique; Pérez, Dolores; Trinquier, Georges; Cuniberti, Gianaurelio; Joachim, Christian; Peña, Diego; Moresco, Francesca

doi:10.1021/acsnano.9b08456

Cited by 105 publications

(114 citation statements)

References 29 publications

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“…18 They also predicted a transition in electronic structure from discrete molecular orbitals to band picture occurs for octacene onwards. 18 Such interconversion in the electronic structure in polyacenes has consequences on its ground state molecular properties such as optical 19 , magnetic 20 , vibrational, 21 and other spectroscopic properties 22 . Here such linear polyacenes are adopted as the spacers in coupling the conformationally restricted nitroxy-diradicals.…”

Section: Introductionmentioning

confidence: 99%

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Kaur

Ali²

2020

Preprint

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The polyacene tend to transition from closed-shell to open-shell singlet systems with increase in the number of linearly fused benzene rings thus, enriching it's electronic as well as magnetic properties. Here, we have probed the role of such a polyacene couplers in mediating the magnetic exchange coupling between nitroxy radicals. For this, magnetic exchange coupling constants (2J) are computed employing broken-symmetry approach within density functional theory (DFT) as well as symmetry-adopted wave function based multi-configuration approach. Within DFT approach, apart from most commonly used exchange-correlation functional (generalized gradient approximation (GGA), meta-GGA, and hybrid) constrained spin density (CDFT) and on-site Coulomb correlation corrected GGA+U functionals have also been used to evaluate the exchange coupling constants in the diradicals. All DFT based methods approximate an exponential increase in the coupling constant values with increase in the length of the coupler. This is indeed an unexpected observation with no experimental report available to such an outcome by DFT calculations. Therefore, the electronic structures for these diradical systems with the increase in number of benzene rings were looked upon thoroughly. The properties like increase in number of degenerate or quasi-degenerate molecular orbitals (MOs), the lowering in energy of low-lying excited states and the development of intrinsic radical character of the coupler add to the complexity in evaluation of 2J values for such diradical systems with DFT approach. Consequently, wave function based multi-reference approach (CAASCF/NEVPT2) has been adopted. The active space has been limited to π-orbitals which are found to play an important role in the magnetic exchange interactions. With increase in the coupler size, the active space even with only π obitals would increase enormously which could not be taken into account even in the CASSCF study. The limited active space calculations also indicate quite strong exchange interaction, thus in principle, supporting the DFT observations of long-range magnetic exchange interactions but not an exponential increase in 2J with length of couplers.

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Section: Introductionmentioning

confidence: 99%

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Kaur

Ali²

2020

Preprint

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“…The latter confers a high reactivity upon acenes of six or more rings, which makes their synthesis challenging. One of the ways that have been devised to circumvent the synthesis difficulties is the surfacesupported synthesis under ultra-high-vacuum (UHV) conditions, which is becoming an increasingly popular approach 5 and has produced the longest polyacenes to date [6][7][8][9][10][11][12][13][14][15][16] .…”

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confidence: 99%

Electronic decoupling of polyacenes from the underlying metal substrate by sp3 carbon atoms

et al. 2020

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On-surface synthesis is becoming an increasingly popular approach to obtain new organic materials. In this context, metallic surfaces are the most commonly used substrates. However, their hybridization with the adsorbates often hinder a proper characterization of the molecule’s intrinsic electronic and magnetic properties. Here we report a route to electronically decouple molecules from their supporting substrates. In particular, we have used a Ag(001) substrate and hydrogenated heptacene molecules, in which the longest conjugated segment determining its frontier molecular orbitals amounts to five consecutive rings. The non-planarity that sp3 atoms impose on the carbon backbone results in electronically decoupled molecules, as demonstrated by scanning tunneling spectroscopy measurements. The charging resonances of the latter imply the presence of double tunneling barriers. We further explain the existing relation between the charging resonance energy and their contrast, as well as with the presence or absence of additional Kondo resonances.

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“…[70] Generally,t he solution synthesis of longer acenes (larger than hexacenes) remains elusive because of their poor stability under ambient conditions, [71] whereas higher acenes up to dodecacene have been achieved through on-surface synthesis. [72][73][74][75] Bisanthene 14can be regarded as alaterally extended perylene (13;F igure 5), and was synthesized for the first time in 1948. [76,77] Recently,h omologous PA Hs with zigzag-edge peripheries,s uch as teranthene (15) and quateranthene (16), [40] were synthesized by expanding the bisanthene core in the longitudinal direction ( Figure 5).…”

Section: Peri-acenesmentioning

confidence: 99%

“…Acenes are linearly cata ‐condensed PAHs, while peri ‐acenes consist of two or more rows of peri ‐fused acenes (Figure 5). [70] Generally, the solution synthesis of longer acenes (larger than hexacenes) remains elusive because of their poor stability under ambient conditions, [71] whereas higher acenes up to dodecacene have been achieved through on‐surface synthesis [72–75] . Bisanthene ( 14 ) can be regarded as a laterally extended perylene ( 13 ; Figure 5), and was synthesized for the first time in 1948 [76, 77] .…”

Section: Peri‐acenesmentioning

confidence: 99%

Synthetic Tailoring of Graphene Nanostructures with Zigzag‐Edged Topologies: Progress and Perspectives

2020

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Experimental and theoretical investigations have revealed that the chemical and physical properties of graphene are crucially determined by their topological structures. Therefore, the atomically precise synthesis of graphene nanostructures is essential. A particular example is graphene nanostructures with zigzag‐edged structures, which exhibit unique (opto)electronic and magnetic properties owing to their spin‐polarized edge state. Recent progress in the development of synthetic methods and strategies as well as characterization methods has given access to this class of unprecedented graphene nanostructures, which used to be purely molecular objectives in theoretical chemistry. Thus, clear insight into the structure–property relationships has become possible as well as new applications in organic carbon‐based electronic and spintronic devices. In this Minireview, we discuss the recent progress in the controlled synthesis of zigzag‐edged graphene nanostructures with different topologies through a bottom‐up synthetic strategy.

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Dodecacene Generated on Surface: Reopening of the Energy Gap

Cited by 105 publications

References 29 publications

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Electronic decoupling of polyacenes from the underlying metal substrate by sp3 carbon atoms

Synthetic Tailoring of Graphene Nanostructures with Zigzag‐Edged Topologies: Progress and Perspectives

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