Polycyclic aromatic hydrocarbons as finite size models of graphene and graphene nanoribbons: Enhanced electron density edge effect

Mishra, Pankaj; Yadav, Anil Kumar

doi:10.1016/j.chemphys.2012.04.005

Cited by 26 publications

(31 citation statements)

References 53 publications

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“…28 In view of this observation, we performed calculations on benzene and PAHs, their monoradicals, and polyradicals at the unrestricted B3LYP/6-31G(d,p) level of theory. We have also employed the unrestricted M06-2X/6-31G(d,p) level of theory 32 in this study.…”

Section: Methods Of Calculationsmentioning

confidence: 98%

Polyradicals of Polycyclic Aromatic Hydrocarbons as Finite Size Models of Graphene: Highly Open-Shell Nature, Symmetry Breaking, and Enhanced-Edge Electron Density

Yadav

Mishra

2013

J. Phys. Chem. A

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Properties of polyradicals (all CH bonds dissociated) of benzene and certain polycyclic aromatic hydrocarbons (PAHs) were studied. The occurrence of symmetry breaking is revealed in going from benzene and the PAHs to their polyradicals. Polyradicals would serve as finite size models of graphene with unpassivated edges in a more realistic way than the PAHs. Monoradicals (one CH bond dissociated) of benzene and all of the PAHs and higher radicals of benzene and one PAH (two to all CH bonds successively dissociated) were also investigated. Reliability of the methodology employed was ascertained by a comparison of our calculated single CH bond dissociation energy of benzene with the available previous experimental and theoretical results. Besides ground-state geometries, the aspects studied include single and successive CH bond dissociation energies, and electron density, molecular electrostatic potential (MEP), and spin density distributions. All of the monoradicals studied were found to have doublet spin multiplicity, while polyradicals with 4 to 16 rings and zigzag or mixed-type edges were found to have spin multiplicities varying from triplet to 11et. Bond lengths and bond angles of rings located at the edges are appreciably modified in going from PAHs to polyradicals. Electron density and spin density are found to be enhanced at the edges of monoradicals and polyradicals of PAHs, as found previously for PAHs. However, MEP maps of polyradicals have significantly different features from those of monoradicals and PAHs, which has a significant implication.

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Section: Methods Of Calculationsmentioning

confidence: 98%

Polyradicals of Polycyclic Aromatic Hydrocarbons as Finite Size Models of Graphene: Highly Open-Shell Nature, Symmetry Breaking, and Enhanced-Edge Electron Density

Yadav

Mishra

2013

J. Phys. Chem. A

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“…For all these systems, we employed the same nomenclature as that adopted in our previous work [9,10]. According to it, in nRm, n represents the number of rows of benzene rings, while m stands for the number of rings in each row, all the edges being of zigzag type.…”

Section: Nomenclature and Presentation Of Resultsmentioning

confidence: 99%

“…In our previous work [9,10], we studied electron density, MEP and spin density distributions in the ground states of several PAHs employing density functional theory and showed that electron density and spin density are enhanced at the edges of these systems. In the present work, lowest vertical singlet-singlet or triplet-triplet π -π * excitation energies, oscillator strengths, chemical hardness, continuous electron density, spin density and MEP distributions in several linear and two-dimensional PAHs of different sizes have been studied.…”

Section: Introductionmentioning

confidence: 99%

“…Several health problems including cardiopulmonary disease and lung cancer are believed to arise due to association of atmospheric aerosols with PAHs [1,2]. In several studies, PAHs have been treated as finite-size models of graphene and graphene nanoribbons (GNRs), which are recently discovered wonderful materials [3][4][5][6][7][8][9][10][11][12]. Study of molecular electrostatic potentials (MEPs) and bond lengths in several PAHs had revealed that MEP values above the carbon rings of the molecules were uniformly weakly negative, particularly above their central portions, indicating low reactivity of those regions, while certain outer CC bonds were found to have considerable double bond character [13][14][15].…”

Section: Introductionmentioning

confidence: 99%

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Lowest Π–Π* electronic transitions in linear and two-dimensional polycyclic aromatic hydrocarbons: enhanced electron density edge effect

Yadav¹,

Mishra²

2013

Molecular Physics

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Polycyclic aromatic hydrocarbons (PAHs) form an important class of molecules as they are ubiquitous, pollute air and cause severe health problems. Lowest vertical π -π * singlet-singlet or triplet-triplet excitation energies and corresponding oscillator strengths were studied for several linear and two-dimensional PAHs employing time-dependent density functional theory. Excited-state electron density, molecular electrostatic potential (MEP) and spin density distributions in the PAHs, along with ground-state chemical hardness, were also studied. It has been found that, generally, excitation energies and oscillator strengths decrease with increase in PAH size, and excitation energies and chemical hardness are strongly linearly correlated. Enhanced electron density edge effect, which was found to occur in the ground states of the molecules, continues to hold in their excited states also. A strong similarity between the ground and π -π * excited-state MEP maps suggests that σ electrons are the main contributors to the enhanced electron density at the edges. Due to their strong electronic absorption transitions in the visible and infrared regions, the PAHs can be used for harnessing solar energy efficiently.

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“…The two-zone electron density image of bare graphene molecule is not new. This feature lays the foundation of a large number of theoreticalcomputational considerations concerning the particular role of edge atoms in graphene begun in 1996 [62] and lasting until today (see a collection of papers [63][64][65][66] and references therein). The graphene objects studied were mainly pencil-made with a regular honeycomb structure described by standard C=C bonds of 1.42 Å in length and identical zigzag and armchair edge atoms.…”

Section: Local Spins In Graphene Molecule Landscapementioning

confidence: 99%

Dirac Material Graphene

Sheka¹

2016

RENSIT

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Abstract. The paper presents an overview on the spin-rooted properties of graphene, supported by numerous experimental and calculation evidence. Correlation of odd p z electrons of the honeycomb lattice meets a strict demand "different orbitals for different spins", which leads to spin polarization of electronic states, on the one hand, and generation of an impressive pool of local spins distributed over the lattice, on the other. These features characterize graphene as a peculiar semimetal with Dirac cone spectrum at particular points of the Brillouin zone. However, spin-orbit coupling (SOC), though small but available, supplemented by dynamic SOC caused by electron correlation, transforms graphene-semimetal into graphene-topological insulator (TI). The consequent topological non-triviality and local spins are proposed to discuss such peculiar properties of graphene as high temperature ferromagnetism and outstanding chemical behavior. The connection of these new findings with difficulties met at attempting to convert graphene-TI (usually taken as SM) into semiconductor one is discussed.

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Polycyclic aromatic hydrocarbons as finite size models of graphene and graphene nanoribbons: Enhanced electron density edge effect

Cited by 26 publications

References 53 publications

Polyradicals of Polycyclic Aromatic Hydrocarbons as Finite Size Models of Graphene: Highly Open-Shell Nature, Symmetry Breaking, and Enhanced-Edge Electron Density

Polyradicals of Polycyclic Aromatic Hydrocarbons as Finite Size Models of Graphene: Highly Open-Shell Nature, Symmetry Breaking, and Enhanced-Edge Electron Density

Lowest Π–Π* electronic transitions in linear and two-dimensional polycyclic aromatic hydrocarbons: enhanced electron density edge effect

Dirac Material Graphene

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