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The role of isomeric effects on the luminescence lifetimes and electrochemistry of oligothienyl-bridged dinuclear tris(2,2′-bipyridine) ruthenium(II) complexes
Mälardalen University, Department of Biology and Chemical Engineering.
Mälardalen University, Department of Biology and Chemical Engineering.
Mälardalen University, Department of Biology and Chemical Engineering.
University of Basel, Switzerland.
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2008 (English)In: European Journal of Inorganic Chemistry, ISSN 1434-1948, no 11, p. 1784-1794Article in journal (Refereed) Published
Abstract [en]

The luminescence lifetimes (in CH 3CN at room temperature) and electrochemical potentials (in CH 3CN) of a range of mono- and bis(bidentate) 2,2′-bipyridine-capped oligothiophene-bridged Ru II complexes based on the 6-(2-thienyl)-2,2′-bipyridine and 4-(2-thienyl)-2,2′-bipyridine motifs have been measured. The redox potentials occurred in a very narrow range and showed only small shifts from that of [Ru(bpy) 3] 2+, which indicates that the inductive effects of the substituents on the 2,2′-bipyridine ligands are very similar across this series. In the complexes that incorporated a bithiophene moiety the oxidation of the bithienyl group occurred at higher potentials than the metal-centered Ru III/II oxidation. No or very weak interaction between the metal cores in the dinuclear complexes was observed. It was found that the luminescence lifetimes of the complexes where the attachment point of the oligothiophene bridge is in the 4-position of a 2,2′-bipyridine ligand were extended compared to [Ru(bpy) 3] 2+, whereas the luminescence was very short-lived (<30 ns) or completely quenched in the complexes where the oligothiophene bridge was attached in the 6-position. The difference in lifetimes is probably due to steric interactions between the thienyl bridge and the auxiliary bipyridyl ligands, resulting in disturbances in coordination symmetry of the metal core.

Place, publisher, year, edition, pages
2008. no 11, p. 1784-1794
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:mdh:diva-4135DOI: 10.1002/ejic.200701118ISI: 000255358200007Scopus ID: 2-s2.0-53349168133OAI: oai:DiVA.org:mdh-4135DiVA, id: diva2:120969
Available from: 2007-11-09 Created: 2007-11-09 Last updated: 2014-06-23Bibliographically approved
In thesis
1. Design, Synthesis and Properties of Bipyridine-capped Oligothiophenes for Directed Energy and Electron Transfer in Molecular Electronic Applications
Open this publication in new window or tab >>Design, Synthesis and Properties of Bipyridine-capped Oligothiophenes for Directed Energy and Electron Transfer in Molecular Electronic Applications
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The earliest landmark in computer technology was construction of the Electronic Numerial Integrator and Computer, ENIAC. Computational switching was performed with vacuum tubes and relays, rather large in size, making this computer rather unwieldy. The next milestone came with the integration of transistors into computers as the switching component. Since then, transistors have been miniaturised dramatically, resulting in the amount of components integrated on a computer chip increasing logarithmically with time. The components are nowadays so small and so densely packed that problems with leak currents and cross-talk can arise and the lower limit for transistor size will soon be reached. In order to meet increasing demands on the size and performance of electronics, a new paradigm is due – the molecular electronics approach.

Oligothiophenes have been shown to possess the physical and chemical characteristics required for electron/energy transport in molecular systems. However oligothiophenes must be electronically coupled to other components within a molecular circuit for them to be functional. In this work, different modes of incorporation of [2,2’]-bipyridinyl functionalities onto the ends of prototypic oligothiophene wires have been examined. The bipyridine connectors allow complexation to metal centres which can then function as a source or sink of electrons in the circuit. Ruthenium tris-bipyridine complexes, in particular, possess interesting electrochemical and photophysical characteristics, making them suitable for use in molecular electronics.

This thesis reports synthetic strategies to a range of novel ligands based on the [2,2’]-bipyridinyl system, together with a study of the redox and fluorescence properties of their ruthenium tris-bipyridine complexes. The mode of connection between the chelating bipyridine and the first member of the oligothiophene chain was found to have a profound effect upon the fluorescence lifetimes and intensities of the resulting complexes. The discovery of complexes exhibiting long and intense fluorescence (a requirement for directed electron/energy transfer within molecular networks) thus forms an important design element in future prototypes.

Place, publisher, year, edition, pages
Institutionen för biologi och kemiteknik, 2007. p. 110
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 54
Keyword
Molecular Electronics, Organic Synthesis, Ruthenium, Pyridyl Complexes, Ligand Design
National Category
Chemical Engineering
Research subject
Biotechnology/Chemical Engineering
Identifiers
urn:nbn:se:mdh:diva-455 (URN)978-91-85485-62-8 (ISBN)
Public defence
2007-12-10, Filen, Verktyget, Smedjegatan 37, Eskilstuna, 10:15
Opponent
Supervisors
Available from: 2007-11-09 Created: 2007-11-09 Last updated: 2016-01-19Bibliographically approved
2. Molecular Electronic Devices based on Ru(II) Thiophenyl Pyridine and Thienopyridine Architecture
Open this publication in new window or tab >>Molecular Electronic Devices based on Ru(II) Thiophenyl Pyridine and Thienopyridine Architecture
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

According to the famous axiom known as Moore’s Law the number of transistors that can be etched on a given piece of ultra-pure silicon, and therefore the computing power, will double every 18 to 24 months. However, around 2020 hardware manufacturers will have reached the physical limits of silicon. A proposed solution to this dilemma is molecular electronics. Within this field researchers are attempting to develop individual organic molecules and metal complexes that can act as molecular equivalents of electronic components such as wires, diodes, transistors and capacitors.

In this work we have synthesized a number of new bi- and terdentate thiophenyl pyridine and pyridyl thienopyridine ligands and compared the electrochemical, structural and photophysical properties of their corresponding Ru(II) complexes with Ru(II) complexes of a variety of ligands based on 6-thiophen-2-yl-2,2'-bipyridine and 4-thiophen-2-yl-2,2'-bipyridine motifs. While the electrochemistry of the Ru(II) complexes were similar to that of unsubstituted [Ru(bpy)3]2+ and [Ru(tpy)2]2+, substantial differences in luminescence lifetimes were found. Our findings show that, due to steric interactions with the auxiliary bipyridyl ligands, luminescence is quenched in Ru(II) complexes that incorporate the 6-thiophen-2-yl-2,2'-bipyridine motif, while it was comparable with the luminescence of [Ru(bpy)3]2+ in the Ru(II) complexes of bidentate pyridyl thienopyridine ligands. The luminescence of the Ru(II) complexes based on the 4-thiophen-2-yl-2,2'-bipyridine motif was enhanced compared to [Ru(bpy)3]2+ which indicates that complexes of this category may be applicable for energy/electron-transfer systems.

At the core of molecular electronics is the search for molecular ON/OFF switches. Based on the ability of the ligand 6-thiophen-2-yl-2,2'-bipyridine to switch reversibly between cyclometallated and non-cyclometallated modes when complexed with Ru(tpy) we have synthesized a number of complexes, among them a bis-cyclometallated switch based on the ligand 3,8-bis-(6-thiophen-2-yl-pyridin-2-yl)-[4,7]phenanthroline, and examined their electrochemical properties. Only very weak electronic coupling could be detected, suggesting only little, if any, interaction between the ruthenium cores.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2010. p. 92
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 86
Keyword
Molecular Electronics, Organic Synthesis, Ruthenium, Pyridyl Complexes, Ligand Design, Fused Ligands
National Category
Chemical Engineering
Research subject
Biotechnology/Chemical Engineering
Identifiers
urn:nbn:se:mdh:diva-10084 (URN)978-91-86135-79-9 (ISBN)
Public defence
2010-09-03, Filen, Smedjegatan 37, Kv. Verktyget, Eskilstuna, 13:00 (English)
Opponent
Supervisors
Available from: 2010-08-09 Created: 2010-08-02 Last updated: 2010-08-19Bibliographically approved
3. The Synthesis of Molecular Switches Based Upon Ru(II) Polypyridyl Architecture for Electronic Applications
Open this publication in new window or tab >>The Synthesis of Molecular Switches Based Upon Ru(II) Polypyridyl Architecture for Electronic Applications
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

According to the famous axiom known as Moore’s Law the number of transistors that can be etched on a given piece of silicon, and therefore the computing power, will double every 18 to 24 months. For the last 40 years Moore’s prediction has held true as computers have grown more and more powerful. However, around 2020 hardware manufac-turers will have reached the physical limits of silicon. A proposed solution to this dilemma is molecular electronics. Within this field researchers are attempting to develop individual organic molecules and metal complexes that can act as molecular equivalents of electronic components such as diodes, transistors and capacitors. By utilizing molecular electronics to construct the next generation of computers processors with 100,000 times as many components on the same surface area could potentially be created.

We have synthesized a range of new pyridyl thienopyridine ligands and compared the electrochemical and photophysical properties of their corresponding Ru(II) complexes with that with the Ru(II) complexes of a variety of ligands based on 6-thiophen-2-yl-2,2´-bipyridine and 4-thiophen-2-yl-2,2´-bipyridine. While the electrochemistry of the Ru(II) complexes were similar to that of unsubstituted [Ru(bpy)3]2+, substantial differences in luminescence lifetimes were found. Our findings show that, due to steric interactions with the auxiliary bipy-ridyl ligands, luminescence is quenched in Ru(II) complexes that in-corporate the 6-thiophen-2-yl-2,2´-bipyridine motif, while it is on par with the luminescence of [Ru(bpy)3]2+ in the Ru(II) complexes of the pyridyl thienopyridine ligands. The luminescence of the Ru(II) com-plexes based on the 4-thiophen-2-yl-2,2´-bipyridine motif was en-hanced compared to [Ru(bpy)3]2+ which indicates that complexes of this category are the most favourable for energy/electron-transfer sys-tems.

At the core of molecular electronics are the search for molecular ON/OFF switches. We have synthesized a reversible double cyclome-tallated switch based on the Ru(tpy) complex of 3,8-bis-(6-thiophen-2-yl-pyridin-2-yl)-[4,7]phenanthroline. Upon treatment with acid/base the complex can be switched between the cyclometallated and the S-bonded form. This prototype has potentially three different states which opens the path to systems based on ternary computer logic.

Place, publisher, year, edition, pages
Institutionen för biologi och kemiteknik, 2007. p. 133
Series
Mälardalen University Press Licentiate Theses, ISSN 1651-9256 ; 77
Keyword
Molecular Electronics, ruthenium, pyridyl complexes, ligand design, ligand synthesis
National Category
Organic Chemistry
Research subject
Biotechnology/Chemical Engineering
Identifiers
urn:nbn:se:mdh:diva-356 (URN)978-91-85485-55-0 (ISBN)
Presentation
2007-08-30, Filen, Verktyget, Smedjegatan 37, Eskilstuna, 13:15
Opponent
Supervisors
Available from: 2007-08-21 Created: 2007-08-21 Last updated: 2016-01-19

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