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Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives of Varying Shapes on Gold: Effect of Laterally Extended ∏-Systems
Department of Chemical and Biological Engineering, Chalmers University of Technology.
Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik. (Materialfysik)
Department of Chemical and Biological Engineering, Chalmers University of Technology.
Department of Chemical and Biological Engineering, Chalmers University of Technology.
Visa övriga samt affilieringar
2007 (Engelska)Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, nr 11, s. 6170-6181Artikel i tidskrift (Refereegranskat) 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

Ort, förlag, år, upplaga, sidor
American Chemical Society , 2007. Vol. 23, nr 11, s. 6170-6181
Nationell ämneskategori
Fysik
Forskningsämne
Fysik
Identifikatorer
URN: urn:nbn:se:kau:diva-2117DOI: 10.1021/la0636964OAI: oai:DiVA.org:kau-2117DiVA, id: diva2:6534
Forskningsfinansiär
VetenskapsrådetTillgänglig från: 2007-05-06 Skapad: 2007-05-06 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
Ingår i avhandling
1. Structure of Self-Assembled Monolayers on Gold Studied by NEXAFS and Photoelectron Spectroscopy
Öppna denna publikation i ny flik eller fönster >>Structure of Self-Assembled Monolayers on Gold Studied by NEXAFS and Photoelectron Spectroscopy
2008 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Self-assembled monolayers (SAMs) provide well-defined and ordered films of molecules spontaneously chemisorbed on a surface. By designing molecules with desired functionalities, such molecular film can be interesting for a range of applications from molecular electronics to catalysis. Important parameters for SAM applications are the film structure and quality, which are dependent on the structure of molecular constituents, the substrate, and the self-assembly process. In this work, SAMs on Au(111) of a variety of functionalized molecules, with thiol and silane headgroups, have been studied using high-resolution X-ray photoemission spectroscopy (HRXPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Infrared reflection absorption spectroscopy (IRRAS), contact angle measurements and Kelvin probe measurements. In particular, the effects of varying the size of the backbone, varying the headgroup, inclusion of a porphyrin tailgroup, different ways of deprotection of the headgroups, and mixed molecular layers have been investigated.

The first part of thesis work is focused on SAMs of oligo(phenyleneethynylene) (OPE) derivatives. First the effect of the extent of the conjugated system on the structure of SAM was investigated. As the lateral π-system in the OPE backbone increases, molecular surface densities become lower and molecular inclinations larger. Subsequently, a bulky porphyrin tailgroup was added onto the OPE molecule. Porphyrin-functionalized OPE with several headgroups were compared and the thioacetyl anchor group was found to form a high quality SAM.

In the second part of the work, the molecular orientation of thiol-derivatized tetraphenylporphyrin layers was studied. The geometry of the molecular layer and the number of linkers that bind to the gold surface depend strongly on preparation schemes, i.e. whether or not the acetyl protection groups on the thiol were removed before adsorption.

Finally, mixed SAMs of a ferrocene-terminated alkanethiol and alkanethiols were studied. By diluting the ferrocene-functionalized molecules in unfunctionalized alkanethiols, the orientational order and the packing density improved. The geometrical structure and the fraction of the ferrocene-terminated molecules can be tuned by controlling the parameters in the preparation scheme.

Ort, förlag, år, upplaga, sidor
Karlstad: Karlstads universitet, 2008. s. 69
Serie
Karlstad University Studies, ISSN 1403-8099 ; 2008:40
Nyckelord
Self-assembled monolayer (SAMs), X-ray photoelectron spectroscopy (XPS), Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Infrared reflection absorption spectroscopy (IRRAS), contact angle measurements, Kelvin probe measurements, oligo(phenyleneethynylene) (OPE), Porphyrin-functionalized OPE, Tetraphenylporphyrin, Ferrocene-terminated alkanethiol, thiol, silane, Au(111)
Nationell ämneskategori
Fysik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-2723 (URN)978-91-7063-200-6 (ISBN)
Disputation
2008-11-07, 21A 342, Karlstad University, 13:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2008-10-20 Skapad: 2008-09-25 Senast uppdaterad: 2011-12-21Bibliografiskt granskad
2. Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives on Gold
Öppna denna publikation i ny flik eller fönster >>Characterization of Self-Assembled Monolayers of Oligo(phenyleneethynylene) Derivatives on Gold
2007 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Institutionen för natur och miljö, 2007
Serie
Karlstad University Studies, ISSN 1403-8099 ; 2007:18
Nyckelord
Self-assembled monolayers, Oligo(phenyleneethynylene), high-resolution X-ray photoemission spectroscopy (HRXPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS)
Nationell ämneskategori
Övrig annan teknik
Forskningsämne
Fysik
Identifikatorer
urn:nbn:se:kau:diva-800 (URN)978-91-7063-121-4 (ISBN)
Presentation
2007-05-21, , 9E 124, Karlstad university, Karlstad, 13:15
Opponent
Handledare
Tillgänglig från: 2007-05-06 Skapad: 2007-05-06

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