Aromaticity and Antiaromaticity in the Excited States of Porphyrin Nanorings

Peeks, Martin D.; Gong, Juliane Q.; McLoughlin, Kirstie; Kobatake, Takayuki; Haver, Renée; Herz, Laura M.; Anderson, Harry L.

doi:10.1021/acs.jpclett.9b00623

Cited by 55 publications

(67 citation statements)

References 56 publications

(117 reference statements)

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“…[13] Electronic excitation can lead to excited-state aromaticity, [4,14] and molecules such as c-P6 are aromatic in their lowest excited states. [15] Many other macrocycles with global aromaticity in the neutral, cationic,a nd excited states have been reported in the last decade. [16][17][18][19][20][21] Porphyrin oligomers have an exceptionally wide range of accessible oxidation states;f or example, c-P6·T6 can be reversibly oxidized up to the 12 + state and reduced to the 6À state.…”

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confidence: 99%

Global Aromaticity and Antiaromaticity in Porphyrin Nanoring Anions

et al. 2019

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Doping,t hrough oxidation or reduction, is often used to modify the properties of p-conjugated oligomers.I n most cases,t he resulting charge distribution is difficult to determine.I ft he oligomer is cyclic and doping establishes global aromaticity or antiaromaticity,then it is certain that the charge is fully delocalized over the entire perimeter of the ring. Herein we showt hat reduction of as ix-porphyrin nanoring using decamethylcobaltocene results in global aromaticity (in the 6À state;[ 90 p]) and antiaromaticity (in the 4À state; [88 p]), consistent with the Hückel rules.A romaticity is assigned by NMR spectroscopya nd density-functional theory calculations.

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Global Aromaticity and Antiaromaticity in Porphyrin Nanoring Anions

et al. 2019

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“…A number of questions can now be posed: It is known that the extent of Bairdaromaticity varies with computational method, 18 but how does it vary between the different macrocycles? Also, to what extent is there an agreement between various types of aromaticity indices on the magnitude of Baird-aromaticity of macrocycles?…”

Section: An Interesting Description Of Baird-aromaticity Is the Descrmentioning

confidence: 99%

“…Our focus is on the potential T1 state Baird- was observed that the extent of T1 state Baird-aromaticity assessed through computations varies strongly with choice of DFT functional. 18 On the other hand, for [n]cycloparaphenylene nanohoops ([n]CPP's) 19 , 20 , 21 -22 in their T1 states it has been considered that long-range corrected functionals are preferred. 23 When going to gradually larger [n]CPP's in their T1 states calculated with UCAM-B3LYP, structures changed from circular with fully delocalized triplet excitations to egg-shaped with the excitations localized to a subset of the para-phenylene units at n > 5.…”

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confidence: 99%

Triplet State Baird-Aromaticity in Macrocycles: Scope, Limitations and Complications

Ayub¹,

Bakouri²,

Smith³

et al. 2020

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The aromaticity of cyclic 4np-electron molecules in their first pp* triplet state (T1), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T1 state Baird-aromaticity in macrocyclic compounds, [n]CM’s, which are cyclic oligomers of four different monocycles (M = para-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 p-electrons in their main conjugation paths we find that for their T1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU’s) retain Baird-aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a 3[n]CFU with a specific n is more strongly Baird-aromatic than the analogous 3[n]CPP while the magnetic indices tell the opposite. To construct large T1 state Baird-aromatic [n]CM’s the design should be such that the T1 state Baird-aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hückel-aromaticity of one or a few monocycles and semi-localized triplet diradical character. Monomers with lower Hückel-aromaticity in S0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T1 state aromaticity we reveal the analogy to the Hückel-aromaticity of the corresponding closed-shell dications, yet, observe stronger Hückel-aromaticity in the macrocyclic dications than Baird-aromaticity in the T1 states of the neutral macrocycles.

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“…( Anti)aromaticity can be induced by perturbing the electronic structure,f or example,b y oxidation or excitation. [15] Many other macrocycles with global aromaticity in the neutral, cationic,a nd excited states have been reported in the last decade. [9] Removal of 4or6electrons from the six-porphyrin nanoring c-P6·T6 leads to macrocyclic global antiaromaticity (80 pelectrons) or aromaticity (78 p-electrons), respectively.…”

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confidence: 99%