The making of ring currents

2016 ◽  
Vol 18 (17) ◽  
pp. 11800-11812 ◽  
Author(s):  
Guglielmo Monaco ◽  
Riccardo Zanasi
Keyword(s):  
Ring Current ◽  
Ring Currents

The π-electron diatropic ring current emerging throughout the trimerization of acetylene to benzene.

Coherent Ring Currents in Chiral Aromatic Molecules Induced by Linearly Polarized UV Laser Pulses

2013 ◽  
Vol 543 ◽  
pp. 381-384 ◽  
Author(s):  
Manabu Kanno ◽  
Hirohiko Koho ◽  
Hirobumi Mineo ◽  
Sheng Hsien Lin ◽  
Yuichi Fujimura
Keyword(s):  
Aromatic Ring ◽  
Quantum Dynamics ◽  
Ring Current ◽  
Molecular System ◽  
Laser Pulses ◽  
Uv Laser ◽  
Aromatic Molecules ◽  
Ring Currents ◽  
Linearly Polarized ◽  
Coherent Ring

In recent years, laser control of electrons in molecular system and condensed matter has attracted considerable attention with rapid progress in laser science and technology [. In particular, control of π-electron rotation in photo-induced chiral aromatic molecules has potential utility to the next-generation ultrafast switching devices. In this paper, we present a fundamental principle of generation of ultrafast coherent ring currents and the control in photo-induced aromatic molecules. This is based on quantum dynamics simulations of π-electron rotations and preparation of unidirectional angular momentum by ultrashort UV laser pulses properly designed. For this purpose, we adopt 2,5-dichloro [(3,6) pyrazinophane (DCPH) fixed on a surface, which is a real chiral aromatic molecule with plane chirality. Here π electrons can be rotated along the aromatic ring clockwise or counterclockwise by irradiation of a linearly polarized laser pulse with the properly designed photon polarization direction and the coherent ring current with the definite direction along the aromatic ring is prepared. This is contrast to ordinary ring current in an achiral aromatic ring molecule with degenerate electronic excited state, which is prepared by a circularly polarized laser [2]. In this case, π electrons rotate along the Z-axis of the laboratory coordinates, while for the present case electrons rotate along the z-axis in molecular Cartesian coordinates. It should be noted that signals originated from the coherent ring currents prepared by linearly polarized ultrashort UV lasers are specific to the chiral molecule of interest.

scholarly journals Global Aromaticity at the Nanoscale

2019 ◽  
Author(s):  
Michel Rickhaus ◽  
Michael Jirasek ◽  
Lara Tejerina ◽  
Henrik Gotfredsen ◽  
Martin D. Peeks ◽  
...  
Keyword(s):  
Small Molecules ◽  
Organic Semiconductors ◽  
Oxidation State ◽  
Single Molecule ◽  
Ring Current ◽  
Electronic Devices ◽  
Three Dimensional ◽  
Average Oxidation State ◽  
Ring Currents ◽  
Cyclic Molecule

<div><p>Aromaticity is an important concept for predicting electronic delocalisation in molecules, particularly for designing organic semiconductors and single-molecule electronic devices. It is most simply defined by the ability of a cyclic molecule to sustain a ring current when placed in a magnetic field. Hückel’s rule states that if a ring has [4n+2] π-electrons, it will be aromatic with an induced magnetisation that opposes the external field inside the ring, whereas if it has 4n π-electrons, it will be antiaromatic with the opposite magnetisation. This rule reliably predicts the behaviour of small molecules, typically with circuits of less than about 22 π-electrons (n = 5). It is not clear whether aromaticity has a size limit and whether Hückel’s rule is valid in much larger macrocycles. Here, we present evidence for global aromaticity in a wide variety of porphyrin nanorings, with circuits of up to 162 π-electrons (n = 40; diameter 5 nm). We show that aromaticity can be controlled by changing the molecular structure, oxidation state and three-dimensional conformation. Whenever a global ring current is observed, its direction is correctly predicted by Hückel’s rule. The magnitude of the current is maximised when the average oxidation state of the porphyrin units is around 0.5–0.7, when the system starts to resemble a conductor with a partially filled valence band. Our results show that aromaticity can arise in large macrocycles, bridging the size gap between ring currents in molecular and mesoscopic rings.</p></div>

scholarly journals About the relationship between auroral electrojets and ring currents

2000 ◽  
Vol 18 (8) ◽  
pp. 874-886 ◽  
Author(s):  
A. Grafe ◽  
Y. I. Feldstein
Keyword(s):  
Ring Current ◽  
Close Correlation ◽  
Recovery Phase ◽  
Current Development ◽  
Storm Main Phase ◽  
Ring Currents ◽  
Magnetometer Data ◽  
Storms And Substorms ◽  
The Relationship ◽  
Statistical Results

Abstract. The relationship between the storm-time ring current and the auroral electrojets is investigated using IMAGE magnetometer data, DSt and H-SYM, and solar wind data. Statistical results as well as the investigation of single events show that the auroral electrojets occur also during nonstorm conditions without storm-time ring current development and even during the storm recovery phase of increasing DSt. A close correlation between electrojet intensity and ring current intensity was not found. Though the eastward electrojet moves equatorward during the storm main phase there is no unequivocal relationship between the movement of the westward electrojet and the ring current development. All these results suggest that the auroral electrojets and the ring current develop more or less independently of each other.Key words: Magnetospheric physics (magnetosphere-ionosphere interactions; storms and substorms)

scholarly journals Magnetically induced ring currents in naphthalene-fused heteroporphyrinoids

2021 ◽  
Author(s):  
Markus Rauhalahti ◽  
D Sundholm ◽  
Mikael P. Johansson
Keyword(s):  
Current Density ◽  
Quantum Chemical ◽  
Ring Current ◽  
Induced Current ◽  
Ring Currents ◽  
Induced Currents

The magnetically induced current density of an intriguing naphthalene-fused heteroporphyrin have been studied, using the quantum-chemical, gauge-including magnetically induced currents (GIMIC) method. The ring-current strengths and current-density pathways for the...

scholarly journals Integration of Global Ring Currents Using the Ampére-Maxwell Law

2021 ◽  
Author(s):  
Raphael Berger ◽  
Maria Dimitrova ◽  
Rinat Nasibullin ◽  
Rashid R. Valiev ◽  
Dage Sundholm
Keyword(s):  
Ring Current ◽  
Magnetic Shielding ◽  
Ring Currents ◽  
Shielding Tensor

Magnetically induced ring current are calculated from the magnetic shielding tensor by employing the Ampére-Maxwell law. The feasibility of the method is demonstrated by integrating the zz component of the...

scholarly journals Global Aromaticity at the Nanoscale

2019 ◽  
Author(s):  
Michel Rickhaus ◽  
Michael Jirasek ◽  
Lara Tejerina ◽  
Henrik Gotfredsen ◽  
Martin D. Peeks ◽  
...  
Keyword(s):  
Small Molecules ◽  
Organic Semiconductors ◽  
Oxidation State ◽  
Single Molecule ◽  
Ring Current ◽  
Electronic Devices ◽  
Three Dimensional ◽  
Average Oxidation State ◽  
Ring Currents ◽  
Cyclic Molecule

<div><p>Aromaticity is an important concept for predicting electronic delocalisation in molecules, particularly for designing organic semiconductors and single-molecule electronic devices. It is most simply defined by the ability of a cyclic molecule to sustain a ring current when placed in a magnetic field. Hückel’s rule states that if a ring has [4n+2] π-electrons, it will be aromatic with an induced magnetisation that opposes the external field inside the ring, whereas if it has 4n π-electrons, it will be antiaromatic with the opposite magnetisation. This rule reliably predicts the behaviour of small molecules, typically with circuits of less than about 22 π-electrons (n = 5). It is not clear whether aromaticity has a size limit and whether Hückel’s rule is valid in much larger macrocycles. Here, we present evidence for global aromaticity in a wide variety of porphyrin nanorings, with circuits of up to 162 π-electrons (n = 40; diameter 5 nm). We show that aromaticity can be controlled by changing the molecular structure, oxidation state and three-dimensional conformation. Whenever a global ring current is observed, its direction is correctly predicted by Hückel’s rule. The magnitude of the current is maximised when the average oxidation state of the porphyrin units is around 0.5–0.7, when the system starts to resemble a conductor with a partially filled valence band. Our results show that aromaticity can arise in large macrocycles, bridging the size gap between ring currents in molecular and mesoscopic rings.</p></div>

scholarly journals (4n +2)π Huckel’s rule of Bn NnC(8-2n) H8 as anti-cancer heterocyclic systems

2020 ◽  
Vol 11 (29) ◽  
pp. 129-150
Author(s):  
Neda SamieiSoofi ◽  
Majid Monajjemi
Keyword(s):  
Aromatic Ring ◽  
Current Density ◽  
Ring Current ◽  
Ring Currents ◽  
Anti Cancer ◽  
Whole Space ◽  
Homo And Lumo ◽  
Localized Orbital ◽  
Homo Lumo ◽  
Magnetic Mechanism

Replacing of Boron and nitrogen atoms in [8] annulene molecule help us for explaining the details of mentioned magnetic mechanism concerning the ring currents of the carbon disappearing in the isoelectronic azabora-hetero-cycles variants (Bn Nn C(8-2n) H82-,n=0,1,2,3 and4 The (4n+2)π systems aromatic on variants of BnNnC(8-2n) H8 (n=0, 1 ,2,3 and 4) via the localized orbital by considering the current density induced have been studied. It has been predicted a four-electron dia-tropic (aromatic) ring current for (4n+2) π aza-bora-hetero-cycles variants of BnNnC (8-2n) H8(n=0,1 ,2,4) and a two-electron para-tropic (anti-aromatic) current for (4n) π. HOMO and LUMO energies and also HOMO/LUMO overlapping in whole space have been calculated. Two forms can be considered, first the HOMO–LUMO transition leads to a para-tropic contribution, and second HOMO–LUMO+1 transitions to the dia-tropic contributions. In addition, the NICS and SNICS values confirm the amounts of aromaticity and anti-aromaticity in those rings.

scholarly journals Morphology of the ring current derived from magnetic field observations

2004 ◽  
Vol 22 (4) ◽  
pp. 1267-1295 ◽  
Author(s):  
G. Le ◽  
C. T. Russell ◽  
K. Takahashi
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Ring Current ◽  
Current System ◽  
Local Times ◽  
Unexpected Result ◽  
Magnetic Field Data ◽  
Dst Index ◽  
Ring Currents ◽  
Magnetospheric Configuration And Dynamics

Abstract. Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ~3 RE and a main westward ring current at ~4–7 RE for all levels of geomagnetic disturbances. In general, the in-situ observations show that the ring current varies as the Dst index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (~0.5MA) and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ~3MA, whereas the total symmetric ring current is ~1MA. Thus, the partial ring current contributes dominantly to the decrease in the Dst index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in the sense of region-2 field-aligned currents, downward into the ionosphere near the dusk and upward out of the ionosphere near the dawn. Key words. Magnetospheric physics (current systems; storms and substorms; magnetospheric configuration and dynamics)

scholarly journals Laser-Control of Ultrafast π-Electron Ring Currents in Aromatic Molecules: Roles of Molecular Symmetry and Light Polarization

2018 ◽  
Vol 8 (12) ◽  
pp. 2347 ◽  
Author(s):  
Manabu Kanno ◽  
Hirohiko Kono ◽  
Yuichi Fujimura
Keyword(s):  
Angular Momentum ◽  
Optical Switching ◽  
Ring Current ◽  
Molecular Vibration ◽  
Vibrational Amplitude ◽  
Electron Dynamics ◽  
Aromatic Molecules ◽  
Ring Currents ◽  
Laser Control ◽  
Ultrafast Electron Dynamics

Being motivated by the recent progress in attosecond laser technology, we theoretically explore the strategy of inducing ultrafast electron dynamics inherent to aromatic molecules, i.e., ring currents by means of polarized laser pulses. The main topic of discussion is how to control the direction of ring currents in an aromatic molecule of low symmetry, for which the design of an efficient control pulse cannot be achieved intuitively. We first consider a system with a single aromatic ring and show that coherent π-electron angular momentum, which oscillates with time, can be produced and controlled by a polarized laser pulse with its ellipticity and orientation properly chosen. Nonadiabatic couplings with molecular vibration gradually weaken the angular momentum, while the vibrational amplitude strongly depends on the polarization of incident light. This suggests the conversion of the polarization dependence of ring current into that of subsequent vibration, which may open a way to detect laser-driven ultrafast electron dynamics by vibrational spectroscopy. The laser-control scheme for the ring current is then extended to a molecule with two aromatic rings, which exhibits characteristic phenomena absent in that with a single ring. We demonstrate that two-dimensional switching of the direction of angular momentum is possible in such molecules. In addition, ring current can be localized at a specific ring by tailored lasers. The application of the present control method to polycyclic aromatic hydrocarbons will lead to the development of next-generation organic optical switching devices.

A study on the aromaticity and ring currents of dithienopyridines and dithienobenzene

2018 ◽  
Vol 17 (01) ◽  
pp. 1850006
Author(s):  
Bi Xiao Yun ◽  
Ablikim Kerim
Keyword(s):  
Ring Current ◽  
Resonance Energy ◽  
Ring Structure ◽  
Electron Delocalization ◽  
Aromaticity Index ◽  
Ring Currents ◽  
Middle Ring ◽  
Topological Resonance Energy ◽  
Local Aromaticity

The global aromaticity of dithienopyridine and dithienobenzene isomers was investigated using the topological resonance energy (TRE) and percentage topological resonance energy (%TRE) methods. The effect of variations in the positions of sulfur and nitrogen atoms on [Formula: see text]-electron delocalization is analyzed. The local aromaticity of these isomers is described based on the bond resonance energy (BRE) and circuit resonance energy (CRE) methods. Our BRE and CRE results show that structure of the central six-membered rings has a strong effect on global aromaticity. The aromaticity of these dithienopyridine isomers is enhanced when a complete pyridine unit exists in their middle ring structure, while the aromaticity of the dithienobenzene isomers is enhanced when a complete benzene unit exists in their middle ring structure. For dithienopyridines, our results obtained using the TRE method correlate well with the Bird aromaticity index as reported in the literature. Our ring-current results show that all these compounds are diatropic systems.

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