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Will Heavy-Core Staffanes Function as Hole transporting Mo-lecular Wires? A Computational Investigation
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Biochemistry and Organic Chemistry.
Manuscript (Other academic)
URN: urn:nbn:se:uu:diva-95450OAI: oai:DiVA.org:uu-95450DiVA: diva2:169660
Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2010-01-13Bibliographically approved
In thesis
1. Heavy-Core Staffanes: A Computational Study of Their Fundamental Properties of Interest for Molecular Electronics
Open this publication in new window or tab >>Heavy-Core Staffanes: A Computational Study of Their Fundamental Properties of Interest for Molecular Electronics
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The basic building blocks in molecular electronics often correspond to conjugated molecules. A compound class consisting of rigid rod-like staffane molecules with the heavier Group 14 elements Si, Ge, Sn and Pb at their bridgehead positions has now been investigated. Herein these oligomers are called heavy-core or Si-, Ge-, Sn- or Pb-core staffanes. These compounds benefit from interaction through their bicyclo[1.1.1]pentane monomer units. Quantum chemical calculations were performed to probe their geometries, stabilities and electronic properties associated with conjugation.

The stabilities of the bicyclo[n.n.n]alkane and [n.n.n]propellanes (1 ≤ n ≤ 3) with C, Si, Ge and Sn at the bridgehead positions were studied by calculation of homodesmotic ring strain energies. The bicyclic compounds with n = 1 and Si, Ge or Sn at bridgehead positions have lower strain than the all-carbon compound.

A gradually higher polarizability exaltation is found as the bridgehead element is changed from C to Si, Ge, Sn or Pb. The ratio between longitudinal and average polarizability also increases gradually as Group 14 is descended, consistent with enhanced conjugation in the heavier oligomers.

The localization of polarons in C-, Si- and Sn-core staffane radical cations was calculated along with internal reorganization energies. The polaron is less localized in Si- and Sn-core than in C-core staffane radical cation. The reorganization energies are also lower for the heavier staffanes, facilitating hole mobility when compared to the C-core staffanes.

The effect of the bicyclic structure on the low valence excitations in the UV-spectra of compounds with two connected disilyl segments was also investigated. MS-CASPT2 calculations of 1,4-disilyl- and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.2.1]heptanes and 1,4-disilyl- and 1,4-bis(trimethylsilyl)-1,4-disilabicyclo[2.1.1]hexanes revealed that although the bicyclic cage separates the two disilyl chromophores, there is a strong red-shift of the lowest valence excitations when compared to an isolated disilane.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 80 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 271
Organic chemistry, conjugation, polarizability, Group 14 elements, cage compounds, electronic excitations, quantum chemistry, molecular electronics, Organisk kemi
urn:nbn:se:uu:diva-7492 (URN)978-91-554-6796-8 (ISBN)
Public defence
2007-03-07, B22, BMC, Husargatan 3, Uppsala, 13:15
Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2011-02-07Bibliographically approved

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