Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Gellini, Cristina; Salvi, Pier Remigio

doi:10.3390/sym2041846

Cited by 38 publications

(37 citation statements)

References 339 publications

(587 reference statements)

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“…Additionally, dark transitions are observed at 5.409 eV and 6.068 eV respectively. These results are consistent with the D 6 h point group of benzene, where there are three low‐lying singlet excited states with

^{1} B_{2 u}

^{1} B_{1 u}

, and

^{1} E_{1 u}

symmetries where

^{1} E_{1 u}

is the only dipole allowed transition and is also doubly degenerate …”

Section: Resultssupporting

confidence: 88%

Modeling Magneto‐Photoabsorption Using Time‐Dependent Complex Generalized Hartree‐Fock

et al. 2019

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Magneto-optical spectroscopy provides a glimpse into the hidden electronic structure of molecules and materials that normally cannot be resolved with regular optical absorption spectroscopy. The magneto-optical signal is difficult to simulate computationally due to the necessity of modeling perturbations from both uniform magnetic and oscillating electric fields. In this work, we introduce a time-dependent complex generalized Hartree-Fock framework for calculating electronic magneto-optical spectra of atomic and molecular systems. Complexvalued gauge including atomic orbitals are used in a nonperturbative treatment of the uniform magnetic field. The magneto-photoabsorption spectra of atomic alkalis and aromatic systems are investigated with a focus on understanding how spectroscopic signals change in the presence of a uniform magnetic field. Methodology Magneto-Optical HamiltonianIn the non-relativistic framework, the interaction of an electron with external fields, defined by their vector (A i ) and scalar (U i )[a] T.

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^{1} B_{2 u}

^{1} B_{1 u}

, and

^{1} E_{1 u}

symmetries where

^{1} E_{1 u}

is the only dipole allowed transition and is also doubly degenerate …”

Section: Resultssupporting

confidence: 88%

Modeling Magneto‐Photoabsorption Using Time‐Dependent Complex Generalized Hartree‐Fock

et al. 2019

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show abstract

“…A single electron HOMO→LUMO excitation from the filled doubly degenerate e 1g orbitals to the vacant doubly degenerate e 2u orbitals of benzene generates six electronically excited states; three singlet states ( 1 B 2u , 1 B 1u and 1 E 1u ) and three triplet states ( 3 B 2u , 3 B 1u and 3 E 1u ). 68 A variety of quantum chemical calculations on the lowest excited states have been reported, yet, in all computations the order in energy is uniformly given as 1 B 2u < 1 B 1u < 1 E 1u for the three singlet states and 3 B 1u < 3 E 1u < 3 B 2u for the triplet states. [69][70][71][72][73][74] It is remarkable that both the S 1 state and the T 1 state in benzene are at higher energies (vertical transitions at 4.90 and 3.95 eV) 75,76 than in the isomeric pentafulvene (vertical transitions at 2.35 and 3.45 eV, respectively) 77,78 .…”

Section: Photophysics and Photochemistry Of Benzenementioning

confidence: 99%

The excited state antiaromatic benzene ring: a molecular Mr Hyde?

2015

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The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas.

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“…In the second example, we elucidate the biradical landscape of [8]annulene, representing a class of molecules bearing a high structural flexibility and therefore several isomeric conformations. 32 For this purpose, we employ ASQPM simulations along with the NOON gap as electronic CV and the three-dimensional Wiener number 33 W as a versatile CV s 1 in Eq. 6.…”

Section: B [8]annulenementioning

confidence: 99%

Metadynamics for automatic sampling of quantum property manifolds: exploration of molecular biradicality landscapes

Lindner

Röhr

2019

Phys. Chem. Chem. Phys.

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We present a general extension of the metadynamics allowing for an automatic sampling of quantum property manifolds (ASQPM) giving rise to functional landscapes that are analogous to the potential energy surfaces in the frame of the Born-Oppenheimer approximation. For this purpose, we employ generalized electronic collective variables to carry out biased molecular dynamics simulations in the framework of quantum chemical methods that explore the desired property manifold. We illustrate our method on the example of the "biradicality landscapes", which we explore by introducing the natural orbital occupation numbers (NOONs) as the electronic collective variable driving the dynamics. We demonstrate the applicability of the method on the simulation of p-xylylene and [8]annulene allowing to automatically extract the biradical geometries. In the case of [8]annulene the ASQPM metadynamics leads to the prediction of biradical scaffolds that can be stabilized by a suitable chemical substitution, leading to the design of novel functional molecules exhibiting biradical functionality. arXiv:1909.09005v1 [physics.chem-ph]

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Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Cited by 38 publications

References 339 publications

Modeling Magneto‐Photoabsorption Using Time‐Dependent Complex Generalized Hartree‐Fock

Modeling Magneto‐Photoabsorption Using Time‐Dependent Complex Generalized Hartree‐Fock

The excited state antiaromatic benzene ring: a molecular Mr Hyde?

Metadynamics for automatic sampling of quantum property manifolds: exploration of molecular biradicality landscapes

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