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Sebastien Villaume - One of the best experts on this subject based on the ideXlab platform.

  • aromaticity changes along the lowest triplet state path for c c bond rotation of annulenyl substituted olefins probed by the Electron localization function
    Journal of Physical Chemistry A, 2009
    Co-Authors: Sebastien Villaume
    Abstract:

    The Pi-contribution to the Electron localization function (ELF Pi) was used to analyze changes in the aromaticity of annulenyl-substituted olefins in their lowest triplet state (T-1) when the structure around the olefin C=C bond is twisted from planar to a structure ((3)p*) at which the planes of the two RR'C units are perpendicular The ring closure bifurcation value and the range in the bifurcation values of the ELF Pi basins serve as (anti)aromaticity indicators directly linked to the Electronic structure. Both Huckel's 4n + 2 Pi-Electron rule for aromaticity in the singlet ground state (S-0) and Baird's 4n Pi-Electron rule for aromaticity in the lowest Pi Pi* triplet state are applied. Three olefins with S-0 aromatic (T-1 antiaromatic) substituents and four olefins with T-1 aromatic (So antiaromatic) substituents were studied using the ELF Pi topology at the OLYP/6-311G(d,p) density functional theory level The changes in the substituent ELF Pi. bifurcation values upon rotation about the olefin bond in the T-1 state reveal that aromatic character is recovered for the first three olefins and that it is reduced for the latter ones. These changes in aromatic character are reflected in the shapes of the T-1 potential energy surfaces as a twist away from planar structures in olefins with T-1 antiaromatic substituents is energetically favorable, but that in olefins with T-1 aromatic substituents is unfavorable. Hence, aromaticity change is a driver for a photochemical reaction as for many ground-state reactions

  • triplet state aromaticity of 4nπ Electron monocycles analysis of bifurcation in the π contribution to the Electron localization function
    ChemPhysChem, 2008
    Co-Authors: Sebastien Villaume, Heather A Fogarty
    Abstract:

    The Pi contribution to the Electron localization function (ELF) is used to compare 4nPi- and (4n+2)Pi-Electron annulenes, with particular focus on the aromaticity of 4nPi-Electron annulenes in their lowest triplet state. The analysis is performed on the Electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ab initio levels. Two criteria for aromaticity of all-carbon annulenes are set up: the span in the bifurcation values DeltaBV(ELF(Pi)) should be small, ideally zero, and the bifurcation value for ring closure of the Pi basin RCBV(ELF(Pi)) should be high (> or = 0.7). On the basis of these criteria, nearly all 4nPi-Electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)Pi-Electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclooctatetraene constrained to D4h and D8h symmetry, respectively, the RCBV(ELF(Pi)) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of alpha- and beta-Electrons.

Heather A Fogarty - One of the best experts on this subject based on the ideXlab platform.

  • triplet state aromaticity of 4nπ Electron monocycles analysis of bifurcation in the π contribution to the Electron localization function
    ChemPhysChem, 2008
    Co-Authors: Sebastien Villaume, Heather A Fogarty
    Abstract:

    The Pi contribution to the Electron localization function (ELF) is used to compare 4nPi- and (4n+2)Pi-Electron annulenes, with particular focus on the aromaticity of 4nPi-Electron annulenes in their lowest triplet state. The analysis is performed on the Electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ab initio levels. Two criteria for aromaticity of all-carbon annulenes are set up: the span in the bifurcation values DeltaBV(ELF(Pi)) should be small, ideally zero, and the bifurcation value for ring closure of the Pi basin RCBV(ELF(Pi)) should be high (> or = 0.7). On the basis of these criteria, nearly all 4nPi-Electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)Pi-Electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclooctatetraene constrained to D4h and D8h symmetry, respectively, the RCBV(ELF(Pi)) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of alpha- and beta-Electrons.

Zhou Haitao - One of the best experts on this subject based on the ideXlab platform.

  • PTCDA molecular monolayer on Pb thin films: An unusual {\Pi}-Electron Kondo system and its interplay with a quantum-confined superconductor
    2021
    Co-Authors: Lu Shuangzan, Nam Hyoungdo, Xiao Penghao, Liu Mengke, Guo Yanping, Bai Yusong, Cheng Zhengbo, Deng Jinghao, Li Yanxing, Zhou Haitao
    Abstract:

    The hybridization of magnetism and superconductivity has been an intriguing playground for correlated Electron systems, hosting various novel physical phenomena. Usually, localized d- or f-Electrons are central to magnetism. In this study, by placing a PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) molecular monolayer on ultra-thin Pb films, we built a hybrid magnetism/superconductivity (M/SC) system consisting of only sp Electronic levels. The magnetic moments reside in the unpaired molecular orbital originating from interfacial charge-transfers. We reported distinctive tunneling spectroscoPic features of such a Kondo screened Pi-Electron impurity lattice on a superconductor in the regime of TK>>delta suggesting the formation of a two-dimensional bound states band. Moreover, moir\'e superlattices with tunable twist angle and the quantum confinement in the ultra-thin Pb films provide easy and flexible implementations to tune the interplay between the Kondo physics and the superconductivity, which are rarely present in M/SC hybrid systems.Comment: 4 figure

  • PTCDA molecular monolayer on Pb thin films: An unusual {\Pi}-Electron Kondo system and its interplay with quantum-confined superconductor
    2021
    Co-Authors: Lu Shuangzan, Nam Hyoungdo, Xiao Penghao, Liu Mengke, Guo Yanping, Bai Yusong, Cheng Zhengbo, Deng Jinghao, Li Yanxing, Zhou Haitao
    Abstract:

    The hybridization of magnetism and superconductivity has been an intriguing playground for correlated Electron systems, hosting various novel physics. Usually, localized d- or f-Electrons are central to magnetism. In this study, by placing a PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) molecular monolayer on ultra-thin Pb films, we built a hybrid magnetism/superconductivity (M/SC) system consisting of only sp Electronic levels participating in the magnetic and superconducting (SC) states. Through experimental and theoretical investigations, we found that the magnetic moments originating from interfacial charge-transfers reside in the unpaired molecular orbital. Kondo screening and its interplay with the superconductivity show several striking spectroscoPic features in scanning tunneling spectroscopy measurements that illustrate the distinctiveness of delocalized {\Pi}-Electron magnetic moments with substantial lateral coupling. Moreover, moir\'e superlattices with tunable commensurate twist angle and the quantum confinement in the ultra-thin Pb films provide easy and flexible implementations to tune the magnetic moment concentration, the SC order parameters, and the competition between them, which are rarely present in previous studied M/SC hybrid systems

Marvin L Cohen - One of the best experts on this subject based on the ideXlab platform.

  • defects quasibound states and quantum conductance in metallic carbon nanotubes
    Physical Review Letters, 2000
    Co-Authors: Hyoung Joon Choi, Jisoon Ihm, Steven G Louie, Marvin L Cohen
    Abstract:

    The effects of impurities and local structural defects on the conductance of metallic carbon nanotubes are calculated using an ab initio pseudopotential method within the Landauer formalism. Substitutionally doped boron or nitrogen produces quasibound impurity states of a definite parity and reduces the conductance by a quantum unit (2e{sup 2}/h) via resonant backscattering. These resonant states show strong similarity to acceptor or donor states in semiconductors. The Stone-Wales defect also produces quasibound states and exhibits quantized conductance reduction. In the case of a vacancy, the conductance shows a much more complex behavior than the prediction from the widely used {Pi} -Electron tight-binding model. (c) 2000 The American Physical Society.

Baranac-stojanović Marija - One of the best experts on this subject based on the ideXlab platform.

  • Electron Delocalization in Electron-Deficient Alkenes and Push-Pull Alkenes
    'Wiley', 2017
    Co-Authors: Džambaski Zdravko, Baranac-stojanović Marija
    Abstract:

    We have studied Pi Electron delocalization in Electron- deficient alkenes and push- pull alkenes by means of natural bond orbital analysis at the B3LYP/6-311+ G(d,p) level. The study revealed that the rarely mentioned Pi Electron donation from an Electron-accepting group (Acc) toward the C=C double bond in push-pull alkenes and Electron-deficient alkenes can provide up to 10% of total Pi Electron stabilizing energy of a push-pull system and as much as 45% in a strongly Electron-deficient tetracyanoethene. The Acc -> C= C bond Pi Electron donation is more intense in s-trans than in s-cis conformational arrangement, but is less dependent on Z/E isomerism in push-pull alkenes, being slightly more pronounced in Z isomers. Among different Acc substituents, CN and COO-groups contribute the largest percent of stabilizing energy and NO2 the smallest. Increase in the number of Acc groups increases percentage contribution of Acc -> C= C bond p Electron delocalization to a system stabilization. A difference in Pi*(C=C) orbital occupancy between isomers can be related with their chemical reactivity

  • Electron Delocalization in Electron-Deficient Alkenes and Push-Pull Alkenes
    Wiley-V C H Verlag Gmbh Weinheim, 2017
    Co-Authors: Džambaski Zdravko, Baranac-stojanović Marija
    Abstract:

    We have studied Pi Electron delocalization in Electron- deficient alkenes and push- pull alkenes by means of natural bond orbital analysis at the B3LYP/6-311+ G(d,p) level. The study revealed that the rarely mentioned Pi Electron donation from an Electron-accepting group (Acc) toward the C=C double bond in push-pull alkenes and Electron-deficient alkenes can provide up to 10% of total Pi Electron stabilizing energy of a push-pull system and as much as 45% in a strongly Electron-deficient tetracyanoethene. The Acc - gt C= C bond Pi Electron donation is more intense in s-trans than in s-cis conformational arrangement, but is less dependent on Z/E isomerism in push-pull alkenes, being slightly more pronounced in Z isomers. Among different Acc substituents, CN and COO-groups contribute the largest percent of stabilizing energy and NO2 the smallest. Increase in the number of Acc groups increases percentage contribution of Acc - gt C= C bond p Electron delocalization to a system stabilization. A difference in Pi*(C=C) orbital occupancy between isomers can be related with their chemical reactivity.Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3112