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Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives on Gold
Karlstad University, Faculty of Technology and Science.
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Oligo(phenyleneethynylene) (OPE) molecules are a class of fully conjugated aromatic molecules, that attract attention for their application as “molecular wires” in molecular electronic devices. In this thesis work, self-assembled monolayers (SAMs) formed from a variety of OPE derivatives have been studied. The chemical properties, structure, and packing density of the SAMs have been characterized utilizing techniques such as high-resolution X-ray photoemission spectroscopy (HRXPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), Infrared reflection absorption spectroscopy (IRRAS), contact angle measurements, and atomic force microscopy (AFM).

In a first study, three OPE-derivatives, with benzene, naphthalene and anthracene, respectively, inserted into the backbone, and an acetyl-protected thiophenol binding group were found to form SAMs on Au(111) substrates with lower molecular surface densities and larger molecular inclination as the lateral π-system increases.

In a second study, porphyrin was introduced as the end group to a wire-like molecule such as OPE. The purpose was to obtain well-organized and functionalized surfaces with optical and redox properties. Three porphyrin-functionalized OPEs had different binding groups, an acetyl-protected thiophenol, a benzylic thiol, and a trimethylsilylethynylene group, and were found to form SAMs on gold surfaces with difference in structure and degree of order. The molecules with the acetyl-protected thiophenol binding group were found to form a high quality SAM compared to the other two. This SAM exhibits a well-ordered and densely packed layer.

This study gives rise to a better understanding of SAM formation of OPE derivatives, and will form a base for further investigations of charge transport properties of these molecular films, which is of interest for applications in molecular electronic devices.

Place, publisher, year, edition, pages
Institutionen för natur och miljö , 2007.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2007:18
Keywords [en]
Self-assembled monolayers, Oligo(phenyleneethynylene), high-resolution X-ray photoemission spectroscopy (HRXPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS)
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Physics
Identifiers
URN: urn:nbn:se:kau:diva-800ISBN: 978-91-7063-121-4 (print)OAI: oai:DiVA.org:kau-800DiVA, id: diva2:6536
Presentation
2007-05-21, , 9E 124, Karlstad university, Karlstad, 13:15
Opponent
Supervisors
Available from: 2007-05-06 Created: 2007-05-06
List of papers
1. Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives of Varying Shapes on Gold: Effect of Laterally Extended ∏-Systems
Open this publication in new window or tab >>Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives of Varying Shapes on Gold: Effect of Laterally Extended ∏-Systems
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2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 11, p. 6170-6181Article in journal (Refereed) Published
Abstract [en]

Fully conjugated organic molecules, such as the oligo(phenyleneethynylene) (OPE) systems, are of growing interest within the field of molecular electronics, as is the self-assembly of well-defined molecular thin films with predefined functions. The structure and function of such films are intimately related and governed by the structures of their molecular constituents, through the intermolecular interactions and the interactions between the molecules and the substrate, onto which the film is assembled. Here we report on the synthesis of a series of three OPE derivatives, with the general structure phenylethynylene−aryl−ethynylenephenylene−headgroup, and the structural investigation of the self-assembled monolayers (SAMs) formed from them on Au(111) surfaces. The SAMs were characterized by infrared reflection−absorption spectroscopy, spectroscopic ellipsometry, high-resolution X-ray photoemission spectroscopy, and near-edge X-ray absorption fine structure spectroscopy. The effective thickness of the SAMs was observed to decrease as the π-system of the aryl moiety of the OPE adsorbate was extended perpendicular to its molecular long axis. Changing the aryl moiety from benzene to naphthalene to anthracene resulted in lower molecular surface densities and larger molecular inclination. The average tilt angles for the benzene, naphthalene, and anthracene SAMs were found to be about 30°, 40°, and 42° from the surface normal, respectively. For the largest adsorbate, the anthracene derivative, there is spectroscopic evidence suggesting the existence of nonequivalent binding sites. The differences observed between the SAMs are rationalized in terms of the shape of the adsorbates and the strength of the π−π interactions between them

Place, publisher, year, edition, pages
American Chemical Society, 2007
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-2117 (URN)10.1021/la0636964 (DOI)
Funder
Swedish Research Council
Available from: 2007-05-06 Created: 2007-05-06 Last updated: 2017-12-06Bibliographically approved
2. HRXPS and NEXAFS Study of Self-Assembled Monolayer of Porphyrin- Functionalized Oligo(phenyleneethynylene) on Gold: The Influence of the Binding Group
Open this publication in new window or tab >>HRXPS and NEXAFS Study of Self-Assembled Monolayer of Porphyrin- Functionalized Oligo(phenyleneethynylene) on Gold: The Influence of the Binding Group
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kau:diva-2118 (URN)
Note

Part of Licentiate Thesis: Watcharinyanon, Somsakul / Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives on Gold / 2007 / Licentiatavhandling 

Available from: 2007-05-06 Created: 2007-05-06 Last updated: 2017-12-06Bibliographically approved

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