MCD of Nonaromatic Cyclic π-Electron Systems. 3. The Perimeter Model for Low-Symmetry “Unaromatic” and “Ambiaromatic” Molecules Derived from 4<i>N</i>-Electron [<i>n</i>]Annulenes

Fleischhauer, Jörg; Höweler, Udo; Michl, Josef

doi:10.1021/jp000116h

Cited by 47 publications

(92 citation statements)

References 14 publications

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“…The MCD spectrum of 5b showed a weak but nevertheless distinct Faraday B term at ∼850 nm. Based on the perimeter model18192021, the lowest-energy band of norcorrole monomers should be forbidden owing to the intrashell nature. Accordingly, the absorption and MCD band observed for 5b at ∼850 nm should be ascribed to transitions between the molecular orbitals of the stacked two norcorrole units.…”

Section: Resultsmentioning

confidence: 99%

Stacked antiaromatic porphyrins

et al. 2016

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Aromaticity is a key concept in organic chemistry. Even though this concept has already been theoretically extrapolated to three dimensions, it usually still remains restricted to planar molecules in organic chemistry textbooks. Stacking of antiaromatic π-systems has been proposed to induce three-dimensional aromaticity as a result of strong frontier orbital interactions. However, experimental evidence to support this prediction still remains elusive so far. Here we report that close stacking of antiaromatic porphyrins diminishes their inherent antiaromaticity in the solid state as well as in solution. The antiaromatic stacking furthermore allows a delocalization of the π-electrons, which enhances the two-photon absorption cross-section values of the antiaromatic porphyrins. This feature enables the dynamic switching of the non-linear optical properties by controlling the arrangement of antiaromatic π-systems on the basis of intermolecular orbital interactions.

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Section: Resultsmentioning

confidence: 99%

Stacked antiaromatic porphyrins

et al. 2016

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“…According to the perimeter model, coupling between s À !l À and s À !l + transitions gives rise to a À,+ pattern for the two P bands, while coupling between h + !s + and h À !s + transitions causes a + + ,À pattern. [14] Since a +,À pattern is observed, the coupling between the h + !s + and h À !s + transitions must be dominant for the MCD signals of the present hexaphyrins.…”

Section: Spectroscopic Properties Of the Reduced Formsmentioning

confidence: 97%

“…Since the transition is of an intrashell nature in the perimeter model, the transition is magnetic-dipole allowed, but the absorption and MCD intensities are predicted to be zero. [14] Indeed, the observed absorption and MCD intensities of the S band are very weak. The other four electronic transitions are intershell transitions derived from the HO!SO or SO!LU transition.…”

Section: Spectroscopic Properties Of the Reduced Formsmentioning

confidence: 99%

“…[17] 4N-Electron perimeter model analysis: According to the 4N-electron perimeter model, six frontier p-orbitals are of particular importance. [14] These orbitals are derived from the highest doubly occupied (HO), the singly occupied (SO), and the lowest unoccupied (LO) doubly degenerate orbitals of an ideal 4N-electron perimeter. 4À .…”

Section: Spectroscopic Properties Of the Reduced Formsmentioning

confidence: 99%

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Application of the Perimeter Model to the Assignment of the Electronic Absorption Spectra of Gold(III) Hexaphyrins with [4n+2] and [4n] π‐Electron Systems

Muranaka

Matsushita

Yoshida

et al. 2009

Chemistry A European J

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The electronic excited states of two forms of meso-hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1) have been investigated by density functional calculations and magnetic circular dichroism (MCD) spectroscopy, in order to assign their low-energy excited singlet states. We found that the perimeter model can be successfully applied to the interpretation of the electronic states. In the case of the neutral forms (Au(2)-N, Au-N), the absorption bands observed in the NIR and visible region can be assigned to pi-pi* transitions referred to as the L and B bands, respectively, analogous to the Q and Soret bands of regular porphyrins. In marked contrast with the neutral forms, the absorption bands of the reduced forms (Au(2)-R and Au-R) are attributed to pi-pi* transitions involving six frontier molecular pi orbitals. By applying the 4N-electron perimeter model, the six orbitals are labeled as h(-), h(+), s(-), s(+), l(-), and l(+), while the observed absorption bands can be assigned to the S, N(1), N(2), P(1), and P(2) transitions, in order of increasing energy.

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“…[11][12][13][14][15][16][17] This approach, originally applied to understand the electronic spectra of aromatic hydrocarbons, was subsequently adapted and extended to encompass magnetic circular dichroism (MCD). The perimeter model correctly accounts for the electronic and MCD patterns in numerous compounds that can be derived from either 4N+2 [11][12][13][14] or 4N [15][16][17] p-electron perimeters. In several cases, the theoretical predictions [18] preceded the synthesis of the systems in question and hence necessarily antedated experimental confirmation.…”

Section: Introductionmentioning

confidence: 99%

Electronic Structure, Spectra, and Magnetic Circular Dichroism of Cyclohexa‐, Cyclohepta‐, and Cyclooctapyrrole

Gorski

Köhler

Seidel

et al. 2005

Chemistry A European J

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Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter-model-based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained.

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MCD of Nonaromatic Cyclic π-Electron Systems. 3. The Perimeter Model for Low-Symmetry “Unaromatic” and “Ambiaromatic” Molecules Derived from 4N-Electron [n]Annulenes

Cited by 47 publications

References 14 publications

Stacked antiaromatic porphyrins

Stacked antiaromatic porphyrins

Application of the Perimeter Model to the Assignment of the Electronic Absorption Spectra of Gold(III) Hexaphyrins with [4n+2] and [4n] π‐Electron Systems

Electronic Structure, Spectra, and Magnetic Circular Dichroism of Cyclohexa‐, Cyclohepta‐, and Cyclooctapyrrole

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