Magnetic circular dichroism of non-aromatic cyclic π-electron systems. 2. [1] The perimeter model for high-symmetry ‘unaromatic’ and ‘ambiaromatic’ molecules derived from 4N-electron [n]annulenes

Fleischhauer, Jörg; Höweler, Udo; Michl, Josef

doi:10.1016/s1386-1425(98)00264-9

Cited by 33 publications

(47 citation statements)

References 8 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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“…In recent years, Michl and co-workers reported that the spectral features and electronic states of small nonaromatic cyclic p-electron systems can be interpreted using the 4N-electron [n]annulene perimeter model. [12][13][14][15][16][17] The UV and MCD spectra of this type of compound, such as biphenylenes [16] and pentalenes, [17] were successfully interpreted on the basis of the perimeter model. Six frontier molecular porbitals (h À , h + , s À , s + , l À , and l + ) play an essential role in the low-energy singlet electronic states of the system derived from the 4N-electron perimeter model.…”

Section: Resultsmentioning

confidence: 99%

“…[9][10][11] We demonstrate in this study that the spectral features of the reduced form of the hexaphyrins (Au 2 -R and Au-R) can be rationalized by the 4N-electron version of the perimeter model. [12][13][14][15][16][17] Band assignments of porphyrinoids derived from (4N + 2)-electron annulenes have been extensively studied for over half a century. [18] However, to the best of our knowledge, an analogous treatment of "unaromatic" porphyrinoids derived from 4N-electron annulenes has not been available, so that this study is the first application of the 4N-electron perimeter model to porphyrinoid systems.…”

Section: Introductionmentioning

confidence: 99%

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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Magnetic circular dichroism of non-aromatic cyclic π-electron systems. 2. [1] The perimeter model for high-symmetry ‘unaromatic’ and ‘ambiaromatic’ molecules derived from 4N-electron [n]annulenes

Cited by 33 publications

References 8 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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