Antiaromaticity in Fluorenylidene Dications. Experimental and Theoretical Evidence for the Relationship between the HOMO/LUMO Gap and Antiaromaticity

Mills, Nancy S.; Levy, and Amalia; Plummer, Benjamin F.

doi:10.1021/jo0499266

Cited by 39 publications

(36 citation statements)

References 79 publications

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“…Indeed, in a set of 20 polycyclic dications, the longest wavelength transition as computed by TD-DFT was linearly correlated with ΔE HL (intercept À1.1 eV, slope 1.3 5 ; r 2 = 0.97). [38] A similar correlation is observed for the 10 molecules investigated in this paper (intercept À0.38 eV, slope 0.90; r 2 = 0.96) and the same order for the molecules is obtained considering their HOMO-LUMO or optical gaps (Table 1). Therefore, for the sake of space, we will comment hereafter only the values of the optical gaps.…”

Section: Aromaticity Of Altan-1 Anionssupporting

confidence: 85%

“…Among the many criteria to identify aromaticity (antiaromaticity), [34] we shall consider the presence of large diatropic (paratropic) circulations in the current density field J [35,36] and a large (small) value for the HOMO-LUMO gap and the first electronic transition. [1,[37][38][39] Actually, the last two criteria can be expected to be strongly correlated. Indeed, in a set of 20 polycyclic dications, the longest wavelength transition as computed by TD-DFT was linearly correlated with ΔE HL (intercept À1.1 eV, slope 1.3 5 ; r 2 = 0.97).…”

Section: Aromaticity Of Altan-1 Anionsmentioning

confidence: 99%

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Anionic derivatives of altan‐corannulene

Monaco

Zanasi

2013

J of Physical Organic Chem

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We report computations of excitation energies, magnetizabilities, and current strengths for the dianion, tetraanion, and hexaanion of the previously introduced altan-corannulene, a molecule designed to hold a strong paratropic current. None of these ions has a fully diatropic or paratropic pattern: dianion and tetraanion both have a paratropic/diatropic/diatropic pattern, whereas the hexaanion has a diatropic/paratropic/diatropic pattern, which is the 'mirror-image' of that of the neutral species. The patterns have been interpreted according to the ipsocentric formulation of the current density. Magnetizability and excitation energy suggest that the hexaanion should be an aromatic molecule. The next homologue of altan-corannulene 6-, altan-altan-corannulene 6-, has also been studied. Its large diamagnetizability has been effectively used to model the magnetic response of C 80 6cages.

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Section: Aromaticity Of Altan-1 Anionssupporting

confidence: 85%

Section: Aromaticity Of Altan-1 Anionsmentioning

confidence: 99%

Anionic derivatives of altan‐corannulene

Monaco

Zanasi

2013

J of Physical Organic Chem

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“…Antiaromaticity also leads to a smaller VEE of the first excited state for strongly antiaromatic molecules than for molecules sustaining a weaker ring current. 85,86 Figure 2 shows that the VEE of the S 0 →S 1 transition of the studied molecules becomes systematically smaller with increasing ring-current strength susceptibility. The VEE of the higher excited states are more or less independent of the size of the ring-current strength susceptibility suggesting that the dominating coefficient in Eq.…”

Section: Spectroscopic Properties B3lyp Calculationsmentioning

confidence: 97%

Optical and magnetic properties of antiaromatic porphyrinoids

Valiev

Fliegl

Sundholm

2017

Phys. Chem. Chem. Phys.

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Magnetic and spectroscopic properties of a number of formally antiaromatic carbaporphyrins, carbathiaporphyrins and isophlorins with 4n π electrons have been investigated at density functional theory and ab initio levels of theory. The calculations show that the paratropic contribution to the magnetically induced ring-current strength susceptibility and the magnetic dipole-transition moment between the ground and the lowest excited state are related. The vertical excitation energy (VEE) of the first excited state decreases with increasing ring-current strength susceptibility, whereas the VEE of the studied higher-lying excited states are almost independent of the size of the ring-current strength susceptibility. Strong antiaromatic porphyrinoids, based on the magnitude of the paratropic ring-current strength susceptibility, have small energy gaps between the highest occupied and lowest unoccupied molecular orbitals and a small VEE of the first excited state. The calculations show that only the lowest S → S transition contributes signficantly to the magnetically induced ring-current strength susceptibility of the antiaromatic porphyrinoids. The decreasing optical gap combined with a large angular momentum contribution to the magnetic transition moment from the first excited state explains why molecules III-VII are antiaromatic with very strong paratropic ring-current strength susceptibilities. The S → S transition is a magnetic dipole-allowed electronic transition that is typical for antiaromatic porphyrinoids with 4n π electrons.

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“…We have demonstrated a good relationship between the experimental and calculated electronic spectra for antiaromatic dications. 34 The challenge for the calculation of properties of anions comes from several issues. While DFT methods are generally very good for larger molecular systems, questions have been raised about their use for anions because of a self-interaction error in approximate functionals.…”

Section: Scheme 2 Preparation Of P-substitutedmentioning

confidence: 99%

Reduction of Benzylidene Dibenzo[a,d]cycloheptenes: Over-Reduction of Antiaromatic Dianions to Aromatic Tetraanions

2011

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The antiaromaticity of a series of dianions of p-substituted benzylidene dibenzo[a,d]cycloheptenes was examined through calculated measures of antiaromaticity. The nucleus-independent chemical shifts (NICS) and magnetic susceptibility exaltation both showed substantial antiaromatic character in the benzannulated tropylium anion. When the antiaromaticity was normalized for the area of the ring, these tropylium anions were shown to be among the most antiaromatic anions in the chemical literature. Attempts to make the dianion through reduction with lithium or potassium gave the tetraanion as the only species observable in the 1H NMR spectrum. Quench of the reaction mixture with trimethylsilyl chloride or D2O confirmed the presence of the tetraanion, but only as a small portion of the reaction mixture, with the major product being unreacted starting material. The failure to observe starting material was attributed to similarities in the structures of the starting material and anion radical (first reduction), allowing rapid electron transfer between them. The inability to see the dianion (second reduction) could be the result of the very small HOMO–LUMO gap anticipated for highly antiaromatic species, which would allow access to diradical species. The magnitude of the HOMO–LUMO gap was determined by the difference between the HOMO and LUMO energies from geometry optimization and the lowest energy transition from TD-DFT calculations. The HOMO–LUMO gap for the benzylidene dibenzocycloheptatriene dianions was shown to be much smaller than the HOMO–LUMO gap of species for which 1H NMR spectra had been observed.

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Antiaromaticity in Fluorenylidene Dications. Experimental and Theoretical Evidence for the Relationship between the HOMO/LUMO Gap and Antiaromaticity

Cited by 39 publications

References 79 publications

Anionic derivatives of altan‐corannulene

Anionic derivatives of altan‐corannulene

Optical and magnetic properties of antiaromatic porphyrinoids

Reduction of Benzylidene Dibenzo[a,d]cycloheptenes: Over-Reduction of Antiaromatic Dianions to Aromatic Tetraanions

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