Uncoupled Hartree–Fock Calculations of the Ring‐Current Contribution to the Magnetic Susceptibilities of Conjugated Molecules

1969 ◽  
Vol 50 (6) ◽  
pp. 2375-2381 ◽  
Author(s):  
A. T. Amos ◽  
H. G. Ff. Roberts
Keyword(s):  
Ring Current ◽  
Conjugated Molecules ◽  
Magnetic Susceptibilities ◽  
Hartree Fock ◽  
Current Contribution

Ab initio Hartree-Fock Investigation of π-Conjugated Compounds Presenting Large βv/βe Ratio: Merocyanines

1998 ◽  
Vol 63 (9) ◽  
pp. 1295-1308 ◽  
Author(s):  
Benoît Champagne ◽  
Thierry Legrand ◽  
Eric A. Perpete ◽  
Olivier Quinet ◽  
Jean-Marie André
Keyword(s):  
Ab Initio ◽  
First Hyperpolarizability ◽  
Conjugated Molecules ◽  
Hartree Fock ◽  
Experimental Discovery ◽  
Conjugated Compounds ◽  
Molecular Frame

CHF/6-311G* calculations of the first electronic and vibrational hyperpolarizabilities reveal that merocyanines present a substantial βv/βe ratio under their quinonoid nonpolar form. It originates from a large vibrational first hyperpolarizability whereas its electronic counterpart is small for this class of push-pull π-conjugated molecules. The transition from the quinonoid to the aromatic configuration is accompanied by an increase of βe and a decrease of the βv/βe ratio as well as by a ≈ 180° rotation in the plane of the molecule of βe and βv with respect to the molecular frame. Our results support the recent experimental discovery that antiparallel aggregation of aromatic and quinonoid forms of merocyanine is energetically favoured and that their first hyperpolarizabilities, which combine constructively, present both electronic and non purely electronic origins.

scholarly journals How Aromatic Are Molecular Nanorings? The Case of a Six-Porphyrin Nanoring

2021 ◽  
Author(s):  
irene casademont-reig ◽  
Raúl Guerrero-Avilés ◽  
Eloy Ramos-Cordoba ◽  
Miquel Torrent-Sucarrat ◽  
Eduard Matito
Keyword(s):  
Low Temperatures ◽  
Ring Current ◽  
Computational Method ◽  
Oxidation States ◽  
Aromatic Rings ◽  
Persistent Currents ◽  
Conjugated Molecules ◽  
Strong Magnetic Fields ◽  
The Poor ◽  
Computational Calculations

<div> <div> <div> <p>Large conjugated rings give rise to novel promising structures that can sustain persistent currents at low temperatures even in the presence of strong magnetic fields. One of the most interesting such molecules was recently synthesized [Anderson et al., Nature, 2017, 541, 3512] in the form of a six-porphyrin nanoring structure, which, according to the authors, in its +6-oxidation state (c-P66+) sustained an aromatic ring current involving 78π electrons; one of the largest aromatic rings ever produced. In this paper, we have provided compelling evidence that this molecule is not aromatic, as it was incorrectly inferred from computational calculations that suffer from large delocalization errors. A thorough analysis of four oxidation states of the six-porphyrin nanoring re- veals that the main reason behind the poor aromaticity of these nanorings is the low delocalization in the transition from the porphyrins to the bridging butadiyne linkers, which disrupts the overall conjugated circuit. These results highlight the importance of choosing an adequate computational method to study large conjugated molecules and the appropriate aromaticity descriptors to identify the part of the molecule that is responsible for the loss of aromaticity. We believe the strategy here employed will be helpful in designing new large aromatic molecular nanorings. </p> </div> </div> </div>

Modeling Substituent-Dependence of the Twist and Shielding in a Series of 4-Substituted N-(4-Nitrobenzylidene)anilines

2004 ◽  
Vol 69 (8) ◽  
pp. 1566-1576 ◽  
Author(s):  
Vladimír Proks ◽  
Miroslav Holík
Keyword(s):  
Chemical Shift ◽  
Ab Initio ◽  
Density Functional ◽  
Ring Current ◽  
Functional Theory ◽  
H Nmr ◽  
Current Contribution ◽  
Monosubstituted Benzenes ◽  
Experimental Chemical Shift

A series of 15 4-substituted N-(4-nitrobenzylidene)anilines was synthesized and studied by 1H NMR spectroscopy. Their ab initio calculated geometries and the shielding as expressed by aromatic ring currents were used in correlation analysis. The geometries were fully optimized using density functional theory B3LYP/6-311G** approaches. For the determination of the ring current contribution to the shielding of azomethine hydrogens Hα was used direct ab initio calculation of the chemical shielding in a model system. Experimental chemical shift values free of these contributions were successfully correlated with increments ap of chemical shift for monosubstituted benzenes. In the same manner, the contribution of the anisotropy of C=N double bond to Hm hydrogen were calculated and values of the Hm chemical shift free of this contribution were successfully correlated with increments of chemical shift am.

Hartree-fock instability in connection with the structure and geometry of some conjugated molecules

1980 ◽  
Vol 71 (2) ◽  
pp. 284-289 ◽  
Author(s):  
B.Ya. Simkin ◽  
M.N. Glukhovtsev ◽  
V.I. Minkin
Keyword(s):  
Conjugated Molecules ◽  
Hartree Fock

scholarly journals How Aromatic Are Molecular Nanorings? The Case of a Six-Porphyrin Nanoring

2021 ◽  
Author(s):  
irene casademont-reig ◽  
Raúl Guerrero-Avilés ◽  
Eloy Ramos-Cordoba ◽  
Miquel Torrent-Sucarrat ◽  
Eduard Matito
Keyword(s):  
Low Temperatures ◽  
Ring Current ◽  
Computational Method ◽  
Oxidation States ◽  
Aromatic Rings ◽  
Persistent Currents ◽  
Conjugated Molecules ◽  
Strong Magnetic Fields ◽  
The Poor ◽  
Computational Calculations

<div> <div> <div> <p>Large conjugated rings give rise to novel promising structures that can sustain persistent currents at low temperatures even in the presence of strong magnetic fields. One of the most interesting such molecules was recently synthesized [Anderson et al., Nature, 2017, 541, 3512] in the form of a six-porphyrin nanoring structure, which, according to the authors, in its +6-oxidation state (c-P66+) sustained an aromatic ring current involving 78π electrons; one of the largest aromatic rings ever produced. In this paper, we have provided compelling evidence that this molecule is not aromatic, as it was incorrectly inferred from computational calculations that suffer from large delocalization errors. A thorough analysis of four oxidation states of the six-porphyrin nanoring re- veals that the main reason behind the poor aromaticity of these nanorings is the low delocalization in the transition from the porphyrins to the bridging butadiyne linkers, which disrupts the overall conjugated circuit. These results highlight the importance of choosing an adequate computational method to study large conjugated molecules and the appropriate aromaticity descriptors to identify the part of the molecule that is responsible for the loss of aromaticity. We believe the strategy here employed will be helpful in designing new large aromatic molecular nanorings. </p> </div> </div> </div>

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