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Impact of Ground- and Excited-State Aromaticity on Cyclopentadiene and Silole Excitation Energies and Excited-State Polarities
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Fysikalisk-organisk kemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Fysikalisk-organisk kemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Fysikalisk-organisk kemi.
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2014 (Engelska)Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, nr 30, s. 9295-9303Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A new qualitative model for estimating the properties of substituted cyclopentadienes and siloles in their lowest pi pi* excited states is introduced and confirmed through quantum chemical calculations, and then applied to explain earlier reported experimental excitation energies. According to our model, which is based on excited-state aromaticity and antiaromaticity, siloles and cyclopentadienes are cross-hyperconjugated "aromatic chameleons" that adapt their electronic structures to conform to the various aromaticity rules in different electronic states (Huckel's rule in the pi(2) electronic ground state (S-0) and Baird's rule in the lowest pi pi* excited singlet and triplet states (S-1 and T-1)). By using pen-and-paper arguments, one can explain polarity changes upon excitation of substituted cyclopentadienes and siloles, and one can tune their lowest excitation energies by combined considerations of ground-and excited-state aromaticity/antiaromaticity effects. Finally, the "aromatic chameleon" model can be extended to other monocyclic compound classes of potential use in organic electronics, thereby providing a unified view of the S-0, T-1, and S-1 states of a range of different cyclic cross-pi-conjugated and cross-hyperconjugated compound classes.

Ort, förlag, år, upplaga, sidor
2014. Vol. 20, nr 30, s. 9295-9303
Nyckelord [en]
aromaticity, conjugation, density functional calculations, electronic structure, organic electronics
Nationell ämneskategori
Fysikalisk kemi
Identifikatorer
URN: urn:nbn:se:uu:diva-231122DOI: 10.1002/chem.201402577ISI: 000339568800022OAI: oai:DiVA.org:uu-231122DiVA, id: diva2:743659
Tillgänglig från: 2014-09-04 Skapad: 2014-09-04 Senast uppdaterad: 2018-04-23Bibliografiskt granskad
Ingår i avhandling
1. Hyperconjugation in Group 14 Organic Compounds: Design and Property Investigations
Öppna denna publikation i ny flik eller fönster >>Hyperconjugation in Group 14 Organic Compounds: Design and Property Investigations
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Nowadays π-conjugated molecules are widely used as materials for devices in organic and molecular electronics. This is due to the ability of such molecules to conduct electricity. However, π-conjugation leads to molecular rigidness and associated lower solubility, which limits possible applications. Meanwhile, there are other types of conjugation that do not cause molecular rigidness but still provide conductivity. One of them is so called hyperconjugation. While π-conjugation involves only p atomic orbitals, hyperconjugation is characterized by interaction of π and σ orbitals. Hyperconjugation is normally weaker than π-conjugation, thus, in order to get strongly hyperconjugated molecules they should be enhanced in some way.

In this thesis, I describe methods for design of strongly hyperconjugated molecules. It is possible to increase the strength of hyperconjugation by various methods and some of them are discussed. We performed quantum chemical calculations in order to investigate optical and geometric properties of the hyperconjugated molecules and evaluate the relative strength of hyperconjugation. In some cases, results of calculations were compared with experimental results aiming to confirm the relevance of the calculations. First, we have investigated how the change of group 14 elements in the 1,4-ditetrelocyclohexa-2,5-dienes influence the hyperconjugation strength. Next, the substituent effect was considered in fulvenes and their hyperconjugated analogs. We showed this effect from the perspective of the substituents influence on the aromatic properties of molecules in the ground and first electronically excited states. Further, the gradual shift when going from monomer to oligomers were investigated. For this hyperconjugated oligomers were constructed from 1,4-disilacyclohexa-2,5-diene and cyclobutadisilole fragments. Additionally we showed the influence of electron withdrawing and electron donating groups on hyperconjugation in siloles and 1,4-disilacyclohexa-2,5-dienes. Finally, hyperconjugation was investigated in a set of silicon-containing omni-hyperconjugated compounds.

The results obtained from this research showed that hyperconjugation strength can be increased significantly up to levels comparable to purely π-conjugated molecules. We hope that these results will be useful in development of other hyperconjugated small molecules, oligomers, and polymers, which can be further used as material for electronic devices.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2017. s. 61
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1613
Nyckelord
1, 4-disilacyclohexa-2, 5-diene, aromaticity, computational chemistry, conjugation, cross-hyperconjugation, hyperconjugation, group 14 elements, organosilicon chemistry, silole
Nationell ämneskategori
Organisk kemi
Identifikatorer
urn:nbn:se:uu:diva-336192 (URN)978-91-513-0190-7 (ISBN)
Disputation
2018-02-09, Häggsalen, Ångström laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-01-19 Skapad: 2017-12-12 Senast uppdaterad: 2018-03-07
2. Influence of Aromaticity on Excited State Structure, Reactivity and Properties
Öppna denna publikation i ny flik eller fönster >>Influence of Aromaticity on Excited State Structure, Reactivity and Properties
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2018. s. 55
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1679
Nyckelord
photochemistry, aromaticity, computational chemistry
Nationell ämneskategori
Organisk kemi Teoretisk kemi
Forskningsämne
Kemi med inriktning mot organisk kemi
Identifikatorer
urn:nbn:se:uu:diva-349229 (URN)978-91-513-0354-3 (ISBN)
Disputation
2018-06-14, room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-05-22 Skapad: 2018-04-23 Senast uppdaterad: 2018-09-27

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