The lowest nπ* states of heteroaromatics: When and in what way are they aromatic or antiaromatic?
dc.contributor.author
dc.date.accessioned
2024-07-22T06:50:23Z
dc.date.available
2024-07-22T06:50:24Z
dc.date.issued
2024-05-24
dc.identifier.issn
1089-5639
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dc.description.abstract
Heteroaromatic molecules are found in areas ranging from biochemistry to photovoltaics. We analyze the n,π* excited states of 6π-electron heteroaromatics with in-plane lone pairs (nσ, herein n) and use qualitative theory and quantum chemical computations, starting at Mandado’s 2n + 1 rule for aromaticity of separate spins. After excitation of an electron from n to π*, a (4n + 2)π-electron species has 2n + 2 πα-electrons and 2n + 1 πβ-electrons (or vice versa) and becomes πα-antiaromatic and πβ-aromatic. Yet, the antiaromatic πα- and aromatic πβ-components seldom cancel, leading to residuals with aromatic or antiaromatic character. We explore vertically excited triplet n,π* states (3n,π*), which are most readily analyzed, but also singlet n,π* states (1n,π*), and explain which compounds have n,π* states with aromatic residuals as their lowest excited states (e.g., pyrazine and the phenyl anion). If the πβ-electron population becomes more (less) uniformly distributed upon excitation, the system will have an (anti)aromatic residual. Among isomers, the one that has the most aromatic residual in 3n,π* is often of the lowest energy in this state. Five-membered ring heteroaromatics with one or two N, O, and/or S atoms never have n,π* states as their first excited states (T1 and S1), while this is nearly always the case for six-membered ring heteroaromatics with electropositive heteroatoms and/or highly symmetric (D2h) diheteroaromatics. For the complete compound set, there is a modest correlation between the (anti)aromatic character of the n,π* state and the energy gap between the lowest n,π* and π,π* states (R2 = 0.42), while it is stronger for monosubstituted pyrazines (R2 = 0.84)
dc.description.sponsorship
M.S. and S.E. thank the Spanish Ministerio de Ciencia e Innovación for project PID2020-113711GB-I00/MCIN/AEI/10.13039/501100011033 and the Generalitat de Catalunya for project 2021SGR623. S.E. thanks Universitat de Girona and DIPC for an IFUdG2019 PhD fellowship
dc.format.extent
14 p.
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application/pdf
dc.language.iso
eng
dc.publisher
American Chemical Society (ACS)
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Reproducció digital del document publicat a: https://doi.org/10.1021/acs.jpca.4c02580
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Journal of Physical Chemistry A, 2024, vol. 128, núm. 22, p. 4493-4506
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Articles publicats (D-Q)
dc.rights
Reconeixement 4.0 Internacional
dc.rights.uri
dc.source
Proos Vedin, Nathalie Escayola Gordils, Sílvia Radenković, Slavko Solà i Puig, Miquel Ottosson, Henrik 2024 The lowest nπ* states of heteroaromatics: When and in what way are they aromatic or antiaromatic? Journal of Physical Chemistry A 128 22 4493 4506
dc.subject
dc.title
The lowest nπ* states of heteroaromatics: When and in what way are they aromatic or antiaromatic?
dc.type
info:eu-repo/semantics/article
dc.rights.accessRights
info:eu-repo/semantics/openAccess
dc.relation.projectID
info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2017-2020/PID2020-113711GB-I00/ES/DISEÑO Y SINTESIS DE FULLERENOS PARA LA CONSTRUCCION DE CELDAS SOLARES HIBRIDAS DE PEROVSKITA Y FULERENOS D ALTO RENDIMIENTO. UN ENFOQUE EXPERIMENTAL Y COMPUTACIONAL SINERGICO/
dc.type.version
info:eu-repo/semantics/publishedVersion
dc.identifier.doi
dc.identifier.idgrec
039021
dc.contributor.funder
dc.type.peerreviewed
peer-reviewed
dc.relation.FundingProgramme
dc.relation.ProjectAcronym
dc.identifier.eissn
1520-5215