The Carbon Factory: A laboratory for the chemistry of carbon-rich systems

Lead Research Organisation: Durham University
Department Name: Chemistry

Abstract

In adopting the concept of Moore's Law , the semiconductor industry has underwritten 40 years of societal growth through the provision of immense computing power. The International Technology Roadmap for Semiconductors informs researchers of short and long-term research targets necessary to maintain this growth. The 2007 edition of the roadmap predicts geometric scaling of components will reach the limits of the solid state in 10 - 15 years, and highlights the need to develop hybrid solid-state / molecule devices. Although forecasts of the demise of the top down approach are not new, it is remarkable to see the semiconductor industry endorse hybrid device architectures (i.e. those in which molecular structures are integrated within a CMOS device) as targets within the foreseeable future. To meet these challenges, a firm understanding of how an electron can be manipulated within and transferred around a molecular structure will be required, and how such systems can be immobilised onto semiconductor surfaces will be required.Much of our understanding of intramolecular electron transfer originates from studies of linear compounds M(a)-B-M(b) in which two sites, M(a) and M(b) identical in every respect except charge state, are linked by some bridging structure, B. The fundamental principles of intramolecular electron transfer in these mixed valence compounds have been systematically mapped over the last 40 years, with the importance of the interactions between the sites M(a) and M(b) and the bridge B being clearly identified. Conjugated carbon-rich bridges have been identified as being particularly useful in the construction of mixed-valence systems with strong coupling interactions between the M(a) and M(b) sites.The facile electron transfer processes in linear, carbon-bridged mixed-valence compounds have led to significant interest in such systems as molecular-scale wires in electronic device applications. However, it could be reasonably argued that a molecular-sized wire is not sufficient, and higher-level function must be incorporated into the molecular component if true advantages over conventional solid state devices are to be realised. The concepts of charge-transfer in 2-D and 3-D molecular systems have attracted attention from the point of view of designing molecular materials for transistor-like molecular electronic components and molecular switches in which the state of one site can influence the nature of the interactions between the others. Multi-site mixed-valence complexes have been proposed as elements for the construction of quantum cellular automata (QCA)-based logic gates and memory cells. Despite the conceptual simplicity of branched (e.g. X and Y shaped) mixed-valence systems, it has proven difficult to prepare a branched ligand core that permits strong electronic coupling between multiple (more than two) remote sites, and relatively little is known about the mechanisms of charge transfer in these systems. In contrast to linear M(a)-B-M(b) systems, mixed valence systems featuring more than two redox sites, termed here multi-site for convenience, are not well-represented, and generally limited to linear arrays M(a)-B-M(b)-B-M(c). This proposal sets out to develop the synthetic chemistry associated with branched carbon-based bridging ligands and multi-site mixed-valence compounds, studies of electron-transfer within these 2-D conjugated compounds, and mechanisms through which these complexes can be attached to semi-conductor surfaces. A number of aside projects are also described, which initiate new lines of investigation in the chemistry of the longer cumulenes, the role of carbon-rich organometallics in the synthesis of fullerenes and carbon nanotubes, discotic liquid crystals comprised of redox-active mesogens and the role of vibrational coupling on electron-transfer reactions.

Publications

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Bruce M (2013) Some Ruthenium Derivatives of Penta-1,4-diyn-3-one in Organometallics

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Kaur I (2013) Modification of electrode surfaces by self-assembled monolayers of thiol-terminated oligo(phenyleneethynylene)s. in Chemphyschem : a European journal of chemical physics and physical chemistry

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Weber L (2013) Electrochemical and spectroelectrochemical studies of C-benzodiazaborolyl-ortho-carboranes. in Dalton transactions (Cambridge, England : 2003)

 
Description This Fellowship led to impacts in the understanding of electron-transfer chemistry, from model mixed-valence systems to molecular electronics. From this grant, new netowrks were established, allowing the novel complexes and compounds prepared in the group to be studied within single molecule junctions and by advanced theory.
Exploitation Route The new surface contacting groups that have been identified and studied have led to better understanding of the metal-molecule interface and design rules for molecular electronic devices. The work with mixed-valence systems has led to new ideas concerning the challenges of assigning compounds to strict classes of 'localised' or 'delocalised' electronic structures.
Sectors Chemicals

Other

 
Description Electrochemically Gated Single Molecule FETs
Amount £357,325 (GBP)
Funding ID EP/K007548/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 05/2013 
End 06/2016
 
Description Collaboration with Prof Martin Kaupp, TU Berlin 
Organisation Technical University Berlin
Country Germany 
Sector Academic/University 
PI Contribution A collaboration with Professor Kaupp at TU Berlin has been developed specifically to allow computational analysis and interpretation of charge transfer transitions in carbon-rich systems. A student from the Kaupp group (Matthias Parthey) spent 6 months in Durham working on data from the Low group to improve both interpretations of data and refine computational methods. This collaboration permitted deeper insight into charge transfer transitions and the resulting spectroscopic features than before. A significant result has been identification of conformers in the appearance of the charge transfer bands and the dynamic nature of the electronic character of our systems. With emerging data relating to the role of conformers on the behavior of molecular materials in molecular junctions we are now closer to correlations of solution and junction characteristics.
Start Year 2012
 
Description Single molecule electronics measurements with University of Liverpool 
Organisation University of Liverpool
Country United Kingdom 
Sector Academic/University 
PI Contribution A new collaboration with Professors Richard Nichols and Simon Higgins (University of Liverpool) to study single molecule conductance of carbon-rich structures. A new collaboration with Nichols and Higgins that has led to numerous papers and new funding opportunities. The capacity to obtain single molecule conductance data from our systems has allowed us to proceed away from solution only studies.
Start Year 2010