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Energetics of Baird aromaticity supported by inversion of photoexcited chiral [4n]annulene derivatives
Univ Tokyo, Dept Chem & Biotechnol, Sch Engn, Bunkyo Ku, 7-3-1 Hongo, Tokyo 1138656, Japan..
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Yonsei Univ, Spect Lab Funct Elect Syst, Seoul 120749, South Korea.;Yonsei Univ, Dept Chem, Seoul 120749, South Korea..
Osaka Univ, Dept Appl Chem, Grad Sch Engn, 2-1 Yamada Oka, Suita, Osaka 5650871, Japan..
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2017 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 346Article in journal (Refereed) Published
Abstract [en]

For the concept of aromaticity, energetic quantification is crucial. However, this has been elusive for excited-state (Baird) aromaticity. Here we report our serendipitous discovery of two nonplanar thiophene-fused chiral [4n]annulenes Th4COT Saddle and Th6CDH Screw, which by computational analysis turned out to be a pair of molecules suitable for energetic quantification of Baird aromaticity. Their enantiomers were separable chromatographically but racemized thermally, enabling investigation of the ring inversion kinetics. In contrast to Th6CDH Screw, which inverts through a nonplanar transition state, the inversion of Th4COT Saddle, progressing through a planar transition state, was remarkably accelerated upon photoexcitation. As predicted by Baird’s theory, the planar conformation of Th4COT Saddle is stabilized in the photoexcited state, thereby enabling lower activation enthalpy than that in the ground state. The lowering of the activation enthalpy, i.e., the energetic impact of excited-state aromaticity, was quantified experimentally to be as high as 21–22 kcal mol–1.

Place, publisher, year, edition, pages
2017. Vol. 8, article id 346
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:uu:diva-333965DOI: 10.1038/s41467-017-00382-1ISI: 000408375700010OAI: oai:DiVA.org:uu-333965DiVA, id: diva2:1165383
Available from: 2017-12-13 Created: 2017-12-13 Last updated: 2018-04-23Bibliographically approved
In thesis
1. Influence of Aromaticity on Excited State Structure, Reactivity and Properties
Open this publication in new window or tab >>Influence of Aromaticity on Excited State Structure, Reactivity and Properties
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes work that could help development of new photochemical reactions and light-absorbing materials. Focus is on the chemical concept "aromaticity" which is a proven conceptual tool in developing thermal chemical reactions. It is here shown that aromaticity is also valuable for photochemistry. The influence of aromaticity is discussed in terms of structure, reactivity and properties. With regard to structure, it is found that photoexcited molecules change their structure to attain aromatic stabilization (planarize, allow through-space conjugation) or avoid antiaromatic destabilization (pucker). As for reactivity, it is found that stabilization/destabilization of reactants decrease/increase photoreactivity, in accordance with the Bell-Evans-Polanyi relationship. Two photoreactions based on excited state antiaromatic destabilization of the substrates are reported. Finally, with respect to properties, it is shown that excited state energies can be tuned by considering aromatic effects of both the electronic ground state and the electronically excited states. The fundamental research presented in this thesis forms a foundation for the development of new photochemical reactions and design of compounds for new organic electronic materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 55
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1679
Keywords
photochemistry, aromaticity, computational chemistry
National Category
Organic Chemistry Theoretical Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-349229 (URN)978-91-513-0354-3 (ISBN)
Public defence
2018-06-14, room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2018-05-22 Created: 2018-04-23 Last updated: 2018-09-27

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Jorner, KjellOttosson, Henrik

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