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Charge transfer through cross-hyperconjugated versus cross-pi-conjugated bridges: an intervalence charge transfer study
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk 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.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
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2013 (Engelska)Ingår i: Chemical Science, ISSN 2041-6520, Vol. 4, nr 9, s. 3522-3532Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Recently there has been much interest in electron transfer and transport through cross-conjugated molecules as interesting test cases for the interplay between molecular and electronic structure as well as potential motifs in the design of new compounds for molecular electronics. Herein we expand on this concept and present the synthesis and characterization of a series of four organic mixed-valence dyads to probe the effect of the bridge structure on the electronic coupling. The electronic coupling between two triarylamine units could be mediated either by cross-hyperconjugation through a saturated ER2 bridge (E = C or Si, R = alkyl or silyl group), or via a cross-conjugated pi-system. The aim of the study is to compare the electron transfer through the various saturated bridges to that of a cross-pi-conjugated bridge. The electronic coupling in these mixed-valence compounds was determined by analysis of intervalence charge transfer bands, and was found to be in the range of 100-400 cm(-1). A complementary DFT and TD-DFT study indicated that the electronic coupling in the dyads with saturated ER2 segments is highly conformer dependant. Furthermore, the calculations showed that two types of interactions contribute to the electronic coupling; a through-bond cross-(hyper)conjugation mechanism and a through-space mechanism. Taken together, these findings suggest the possibility for new architectures for molecular electronics applications utilizing cross-hyperconjugation through properly selected saturated segments which have comparable electron transfer characteristics as regular cross-pi-conjugated molecules.

Ort, förlag, år, upplaga, sidor
2013. Vol. 4, nr 9, s. 3522-3532
Nationell ämneskategori
Naturvetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-208680DOI: 10.1039/c3sc50844gISI: 000322391800021OAI: oai:DiVA.org:uu-208680DiVA, id: diva2:653895
Tillgänglig från: 2013-10-07 Skapad: 2013-10-07 Senast uppdaterad: 2014-06-30Bibliografiskt granskad
Ingår i avhandling
1. Conjugation in Organic Group 14 Element Compounds: Design, Synthesis and Experimental Evaluation
Öppna denna publikation i ny flik eller fönster >>Conjugation in Organic Group 14 Element Compounds: Design, Synthesis and Experimental Evaluation
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2014. s. 70
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1140
Nyckelord
conjugation, conductance, electronic structure, Group 14 elements, hyperconjugation, molecular electronics, organosilicon chemistry
Nationell ämneskategori
Organisk kemi Fysikalisk kemi
Forskningsämne
Kemi med inriktning mot organisk kemi
Identifikatorer
urn:nbn:se:uu:diva-221683 (URN)978-91-554-8929-8 (ISBN)
Disputation
2014-05-27, B42, BMC, Husargatan 3, Uppsala, 13:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-05-06 Skapad: 2014-04-03 Senast uppdaterad: 2014-06-30

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Göransson, ErikEmanuelsson, RikardJorner, KjellMarkle, Todd F.Hammarström, LeifOttosson, Henrik

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