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Exploiting the Aromatic Chameleon Character of Fulvenes for Computational Design of Baird-Aromatic Triplet Ground State Compounds
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
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2019 (English)In: Chemistry - An Asian Journal, ISSN 1861-4728, E-ISSN 1861-471X, Vol. 14, no 10, p. 1870-1878Article in journal (Refereed) Published
Abstract [en]

Due to the reversal in electron counts for aromaticity and antiaromaticity in the closed-shell singlet state (normally ground state, S-0) and lowest * triplet state (T-1 or T-0), as given by Huckel's and Baird's rules, respectively, fulvenes are influenced by their substituents in the opposite manner in the T-1 and S-0 states. This effect is caused by a reversal in the dipole moment when going from S-0 to T-1 as fulvenes adapt to the difference in electron counts for aromaticity in various states; they are aromatic chameleons. Thus, a substituent pattern that enhances (reduces) fulvene aromaticity in S-0 reduces (enhances) aromaticity in T-1, allowing for rationalizations of the triplet state energies (E-T) of substituted fulvenes. Through quantum chemical calculations, we now assess which substituents and which positions on the pentafulvene core are the most powerful for designing compounds with low or inverted E-T. As a means to increase the -electron withdrawing capacity of cyano groups, we found that protonation at the cyano N atoms of 6,6-dicyanopentafulvenes can be a route to on-demand formation of a fulvenium dication with a triplet ground state (T-0). The five-membered ring of this species is markedly Baird-aromatic, although less than the cyclopentadienyl cation known to have a Baird-aromatic T-0 state.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2019. Vol. 14, no 10, p. 1870-1878
Keywords [en]
Baird's rule, excited state aromaticity, fulvenes, quantum chemistry, triplet state energies
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-389826DOI: 10.1002/asia.201801821ISI: 000471307500040PubMedID: 30659757OAI: oai:DiVA.org:uu-389826DiVA, id: diva2:1339459
Funder
Swedish Research CouncilCarl Tryggers foundation Wenner-Gren FoundationsAvailable from: 2019-07-29 Created: 2019-07-29 Last updated: 2019-07-29Bibliographically approved

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El Bakouri, OuissamJorner, KjellDahlstrand, ChristianOttosson, Henrik

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Yadav, SangeetaEl Bakouri, OuissamJorner, KjellDahlstrand, ChristianSola, MiquelOttosson, Henrik
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Department of Chemistry - ÅngströmDepartment of Chemistry - BMC
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Chemistry - An Asian Journal
Organic Chemistry

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