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Cross-hyperconjugation: An unexplored orbital interaction between pi-conjugated and saturated molecular segments
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
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2013 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, no 3, 983-987 p.Article in journal (Refereed) Published
Abstract [en]

Crossing a barrier: Molecules with saturated ER2 units (E=C or Si, R=electron-releasing group) inserted between two π-conjugated segments have electronic and optical properties that resemble those of cross-conjugated molecules (see figure). This cross-hyperconjugation provides a deeper understanding of the conjugation phenomenon, and is an alternative to cross-conjugation in the design of molecules for nano and materials applications.

Place, publisher, year, edition, pages
2013. Vol. 52, no 3, 983-987 p.
Keyword [en]
conjugation, cross-conjugation, Group 14 elements, hyperconjugation, optical tuning
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-194990DOI: 10.1002/anie.201206030ISI: 000313688100036OAI: oai:DiVA.org:uu-194990DiVA: diva2:606928
Available from: 2013-02-21 Created: 2013-02-20 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Conjugation in Organic Group 14 Element Compounds: Design, Synthesis and Experimental Evaluation
Open this publication in new window or tab >>Conjugation in Organic Group 14 Element Compounds: Design, Synthesis and Experimental Evaluation
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on the chemical concept of conjugation, i.e., electron delocalization, and the effect it has on electronic and optical properties of molecules. The emphasis is on electron delocalization across a saturated σ-bonded segment, and in our studies these segments are either inserted between π-conjugated moieties or joined together to form longer chains. The electronic and optical properties of these compounds are probed and compared to those of traditionally π-conjugated compounds. The investigations utilize a combination of qualitative chemical bonding theories, quantum chemical calculations, chemical syntheses and different spectroscopic methods.

Herein, it is revealed that a saturated σ-bonded segment inserted between two π-systems can have optical and electronic properties similar to a cross-conjugated compound when substituents with heavy Group 14 elements (Si, Ge or Sn) are attached to the central atom. We coined the terminology cross-hyperconjugation for this interaction, and have shown it by both computational and spectroscopic means. This similarity is also found in cyclic compounds, for example in the 1,4-disilacyclohexa-2,5-dienes, as we reveal that there is a cyclic aspect of cross-hyperconjugation. Cross-hyperconjugation can further also be found in smaller rings such as siloles and cyclopentadienes, and we show on the similarities between these and their cross-π-conjugated analogues, the fulvenes. Here, this concept is combined with that of excited state aromaticity and the electronic properties of these systems are rationalized in terms of “aromatic chameleon” effects. We show that the optical properties of these systems can be rationally tuned and predicted through the choice of substituents and knowledge about the aromaticity rules in both ground and excited states.

We computationally examine the relation between conjugation and conductance and reveal that oligomers of 1,4-disilacyclohexa-2,5-dienes and related analogues can display molecular cord properties. The conductance through several σ-conjugated silicon compounds were also examined and show that mixed silicon and carbon bicyclo[2.2.2]octane compounds do not provide significant benefits over the open-chain oligosilanes. However, cyclohexasilanes, a synthetic precursor to the bicyclic compounds, displayed conformer-dependent electronic structure variations that were not seen for cyclohexanes. This allowed for computational design of a mechanically activated conductance switch.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1140
Keyword
conjugation, conductance, electronic structure, Group 14 elements, hyperconjugation, molecular electronics, organosilicon chemistry
National Category
Organic Chemistry Physical Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-221683 (URN)978-91-554-8929-8 (ISBN)
Public defence
2014-05-27, B42, BMC, Husargatan 3, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-05-06 Created: 2014-04-03 Last updated: 2014-06-30

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Emanuelsson, RikardNauroozi, DjawedOtt, SaschaOttosson, Henrik

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