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A Computational Investigation of the Substituent Effects on Geometric, Electronic, and Optical Properties of Siloles and 1,4-Disilacyclohexa-2,5-dienes
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. (Nanoteknologi och funktionella material)ORCID iD: 0000-0002-4726-4121
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
2017 (English)In: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 22, no 3, article id 370Article in journal (Refereed) Published
Abstract [en]

Thirty two differently substituted siloles 1a–1p and 1,4-disilacyclohexa-2,5-dienes 2a–2p were investigated by quantum chemical calculations using the PBE0 hybrid density functional theory (DFT) method. The substituents included σ-electron donating and withdrawing, as well as π-electron donating and withdrawing groups, and their effects when placed at the Si atom(s) or at the C atoms were examined. Focus was placed on geometries, frontier orbital energies and the energies of the first allowed electronic excitations. We analyzed the variation in energies between the orbitals which correspond to HOMO and LUMO for the two parent species, here represented as ΔεHL, motivated by the fact that the first allowed transitions involve excitation between these orbitals. Even though ΔεHL and the excitation energies are lower for siloles than for 1,4-disilacyclohexa-2,5-dienes the latter display significantly larger variations with substitution. The ΔεHL of the siloles vary within 4.57–5.35 eV (ΔΔεHL = 0.78 eV) while for the 1,4-disilacyclohexa-2,5-dienes the range is 5.49–7.15 eV (ΔΔεHL = 1.66 eV). The excitation energy of the first allowed transitions display a moderate variation for siloles (3.60–4.41 eV) whereas the variation for 1,4-disilacyclohexa-2,5-dienes is nearly doubled (4.69–6.21 eV). Cyclobutadisiloles combine the characteristics of siloles and 1,4-disilacyclohexa-2,5-diene by having even lower excitation energies than siloles yet also extensive variation in excitation energies to substitution of 1,4-disilacyclohexa-2,5-dienes (3.47–4.77 eV, variation of 1.30 eV).

Place, publisher, year, edition, pages
2017. Vol. 22, no 3, article id 370
National Category
Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
URN: urn:nbn:se:uu:diva-335095DOI: 10.3390/molecules22030370ISI: 000398743500031OAI: oai:DiVA.org:uu-335095DiVA, id: diva2:1161560
Note

Title of manuscript in list of papers in Julius Tibbelin´s thesis: A comparative computational investigation of the substituent effects on geometric, electronic, and optical properties of 1,4-disilacyclo-hexa-2,5- dienes and siloles

Available from: 2017-11-30 Created: 2017-11-30 Last updated: 2018-02-16Bibliographically approved
In thesis
1. Hyperconjugation in Group 14 Organic Compounds: Design and Property Investigations
Open this publication in new window or tab >>Hyperconjugation in Group 14 Organic Compounds: Design and Property Investigations
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 61
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1613
Keywords
1, 4-disilacyclohexa-2, 5-diene, aromaticity, computational chemistry, conjugation, cross-hyperconjugation, hyperconjugation, group 14 elements, organosilicon chemistry, silole
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-336192 (URN)978-91-513-0190-7 (ISBN)
Public defence
2018-02-09, Häggsalen, Ångström laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2018-01-19 Created: 2017-12-12 Last updated: 2018-03-07
2. Organic Heavy Group 14 Element Compounds: A Study of Their Chemical Bonding Properties Directed Towards Applications as Molecular Wires and in Synthesis
Open this publication in new window or tab >>Organic Heavy Group 14 Element Compounds: A Study of Their Chemical Bonding Properties Directed Towards Applications as Molecular Wires and in Synthesis
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The research described herein includes synthesis, spectroscopy, and quantum chemical calculations with focus on the characteristic properties of compounds with bonds between carbon and the heavier Group 14 elements.

The chapters based on the first four papers concern σ- and σ/π-conjugated compounds, although the focus of the first paper is on ring strain of bicyclo[1.1.1]pentanes with C, Si, Ge or Sn at the bridgeheads. The relationship between calculated homodesmotic ring strain energies and through-space distances between the bridgehead atoms was evaluated, and it was found that replacing one of the methylene bridges with phospha-methyl gave both low strain and short through-space distance.

Two kinds of σ/π-interacting systems were analysed with the difference that the σ- and π-bonded segments were either allowed to rotate freely relative each other or frozen into a conformer with maximal σ/π-interaction. The freely rotating systems are star-shaped oligothiophenes linked by heavy alkane segments. Density functional theory (DFT) calculations of hole reorganization energies support the measured hole mobilites. In summary, longer central oligosilane linkages, when compared to shorter, facilitate intermolecular hole-transfer between oligothiophene units.

In 1,4-disilacyclohexa-2,5-dienes, the strength of the π- and pseudo-π interaction depends on the substituents at Si. Vapour phase UV absorption spectroscopy of 2,3,5,6-tetraethyl-1,1,4,4-tetrakis(trimethylsilyl)-1,4-disilacyclohexa-2,5-diene reveals a strong absorption at 273 nm (4.50 eV). Time-dependent DFT calculations further indicate that octastannylated 1,4-disilacyclohexa-2,5-diene has is lowest excited state at 384 nm (3.23 eV). The electronic, geometric and optical properties of substituted 1,4-disilacyclohexa-2,5-dienes were compared with those of the correspondingly substituted siloles. It was found that the lowest excitations of siloles are less tunable than those of 1,4-disilacyclohexa-2,5-dienes.

The final section concerns strongly reverse-polarised 2-amino-2-siloxysilenes formed thermally from carbamylpolysilanes, and their lack of reaction with alcohols. Instead, the carbamylsilane reacts with alcohols giving silyl ethers, leading to a new benign route for alcohol protection.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. p. 81
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 747
Keywords
Silicon, Group 14 Elements, Silenes, Conjugation, Chemical Bonding, Electronic Structure, Protecting Group Chemistry
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-123088 (URN)978-91-554-7820-9 (ISBN)
Public defence
2010-06-04, B42, Husargatan 3, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2010-05-11 Created: 2010-04-23 Last updated: 2018-02-16

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Denisova V, AleksandraTibbelin, JuliusEmanuelsson, RikardOttosson, Henrik

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