Helical orbitals and circular currents in linear carbon wires

Garner, Marc H.; Jensen, Annie Aarup; Hyllested, Louise O. H.; Solomon, Gemma C.

doi:10.1039/c8sc05464a

Cited by 55 publications

(83 citation statements)

References 106 publications

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“…The recent theoretical demonstration by Solomon and co‐workers on the presence of circular currents in molecules featuring Hel‐MOs calls for the development of real systems with Hel‐MOs for spintronics [12] . This emerging technology, which controls the spin of electrons, presents higher energy efficiency and frequency as compared to electronics [13] .…”

Section: Methodsmentioning

confidence: 99%

“…[11] The recent theoretical demonstrationb yS olomon and coworkers on the presence of circular currentsi nm olecules featuring Hel-MOs calls for the development of real systems with Hel-MOs for spintronics. [12] This emerging technology,w hich controlst he spin of electrons,p resents higher energy efficiency and frequency as compared to electronics. [13] In this regard, chiral organic molecules manifesting chiral-induced spin selectivity (CISS) [14] have already shown great advantages in memory devices.…”

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confidence: 99%

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Distinct Helical Molecular Orbitals through Conformational Lock**

Ozcelik

Aranda

Gil‐Guerrero

et al. 2020

Chemistry A European J

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Several theoretical studies have proposed strategies to reach helical molecular orbitals (Hel-MOs) in [n]cumulenes. While chiral even-[n] cumulenes feature Hel-MOs, odd-[n] cumulenes may also present them if the terminal groups lie on different planes. However, the hitherto proposed systems have been either experimentally unfeasible or resulted in opposite pseudodegenerated Hel-MOs, impeding their use in real applicatons. To overcome this challenge, we hereby demonstrate the introduction of a remarkable energy difference between helical orbitals of opposite twist by fixing the torsion angle between the terminal groups in butadiyne fragments. In order to experimentally lock the conformation of the terminal groups, we designed cyclic architectures by combining acetylenes with chiral spirobifluorenes. A straightforward synthetic strategy along with the high stability allowed the isolation and full characterization of systems presenting distinct helical orbitals. Finally, a thorough computational analysis revealed that the most significant optical responses of these systems originate mainly from the exciton coupling between the featured diphenylbutadiyne fragments. This novel strategy opens now access to the development of systems with distinct helical molecular orbitals suitable for their implementation into chiroptical and optoelectronic applications Scheme 1. General representation of acetylene (top left), [2]cumulene (top center), [3]cumulene (top right) and schematic representation of two possible paths for the formation of helical orbitals in [2]cumulenes (bottom left) and acetylenes (bottom right). Black spheres represent functional groups that can be the same or different and grey lobes stand for p atomic orbitals.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Distinct Helical Molecular Orbitals through Conformational Lock**

Ozcelik

Aranda

Gil‐Guerrero

et al. 2020

Chemistry A European J

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“…The reversal of the ring currents at 90° is also intimately linked to this interference effect. 45,57,61 The full transmission plots at 95°, 150° and 180°…”

Section: Polyynic Carbon Wiresmentioning

confidence: 99%

Three Distinct Torsion Profiles of Electronic Transmission Through Linear Carbon Wires

Garner

Bro-Jørgensen²,

Solomon³

2020

Preprint

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The one-dimensional carbon allotrope carbyne, a linear chain of sp-hybridized carbon atoms, is predicted to exist in a polyynic and a cumulenic structure. While molecular forms of carbyne have been extensively characterized, the structural nature is hard to determine for many linear carbon wires that are made in-situ during pulling experiments. Here, we show that cumulenes and polyynes have distinctively different low-bias conductance profiles under axial torsion. We analyze the change of the electronic structure, Landauer transmission, and ballistic current density of the three types of closed-shell molecular carbynes as a function of the torsion angle. Both polyynic, odd-carbon cumulenic, and even-carbon cumulenic carbon wires exhibit helical frontier molecular orbitals when the end-groups are not in a co-planar configuration. This helical conjugation effect gives rise to strong ring current patterns around the linear wires. Only the transmission of even-carbon polyynic wires follows the well-known cosine-squared law with axial torsion that is also seen in biphenyl-type systems. Notably, the transmission of even-carbon cumulenic carbon wires rises with axial torsion from co-planar towards perpendicular orientation of the end-groups. The three distinct transmission profiles of polyynes, odd-carbon cumulenes, and even-carbon cumulenes may allow for experimental identification of the structural nature of linear carbon wires. Their different electron transport properties under axial torsion furthermore underline that, in the molecular limit of carbyne, three different subclasses of linear carbon wires exist.

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“…This has been studied extensively in proteins, [13][14][15][16][17] and pathway control has been achieved via infrared excitations in donor-bridge-acceptor systems. 18 Pathway analyses are also essential for identifying whether electrons follow helical paths in helixshaped molecules 19 or in electronically helical structures, 20 which may be important for understanding chiral induced spin selectivity. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] Circular pathways are closely linked with destructive quantum interference in molecular junctions, [39][40][41] and engineering pathways can be employed as a means of manipulating the transport properties of molecular systems.…”

mentioning

confidence: 99%

“…[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] Circular pathways are closely linked with destructive quantum interference in molecular junctions, [39][40][41] and engineering pathways can be employed as a means of manipulating the transport properties of molecular systems. 42 While a number of theoretical approaches exist for extracting pathway information, 9,14,15,20,39,[43][44][45][46][47][48][49][50][51] access by experimental methods is limited. An experimental technique which is able to provide pathway information is inelastic tunneling spectroscopy (IETS), 1,[52][53][54][55][56] in which signatures of tunneling electrons exciting molecular vibrations are recorded.…”

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confidence: 99%

The Limits of Inelastic Tunneling Spectroscopy for Identifying Transport Pathways

Deffner¹,

Herrmann²

2020

Preprint

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Inelastic Electron Tunneling Spectroscopy (IETS) is a powerful tool to study the properties of molecular junctions. In particular, it is considered useful for extracting information on electron transport pathways. We explore the limits of this approach by comparing computed interatomic transmission pathways with IETS intensities for different molecular junctions, employing a new efficient implementation for evaluating IETS intensities via the mode-tracking algorithm. We find that while a correlation be- tween pathways and IETS intensities indeed holds when vibrations are clearly localized on atoms off the transport pathway, there is no such correlation for molecules with less localized vibrations, even if transport pathways only sample part of the molecule, and even if a statistical analysis over the vibrational modes is made. This could indicate that the significance of IETS signals for transport pathways is limited to molecules with localized vibrational modes.

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Helical orbitals and circular currents in linear carbon wires

Abstract: Disubstituted odd-carbon cumulenes are linear carbon wires with helical π-orbitals, which results in circular current around the wire.

Cited by 55 publications

References 106 publications

Distinct Helical Molecular Orbitals through Conformational Lock**

Distinct Helical Molecular Orbitals through Conformational Lock**

Three Distinct Torsion Profiles of Electronic Transmission Through Linear Carbon Wires

The Limits of Inelastic Tunneling Spectroscopy for Identifying Transport Pathways

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