Porphyrin single molecule wires for nanoelectronics

Lead Research Organisation: University of Liverpool
Department Name: Chemistry


The prime aspiration of molecular nanoelectronics is to fabricate and interconnect molecules that can replace, or at least augment, present silicon based technology, with the molecules functioning as interconnects, switches, transistors or even logic gates. Clearly big challenges exist if such technologies are ever to reach fruition. In this respect, one of the key scientific challenges is to synthesise and reliably connect single molecular wires which can transport charge over long distance and also perform other functions such as rectifying current or storing charge. This proposal is aimed at synthesising extended molecular wires from a class of molecules called porphyrins, whose synthesis and functionalisation is the focus of the Oxford group. These electrical properties of these well-characterised molecules will be investigated at Cardiff and Liverpool, particularly their efficiency as molecular wires, their contacts with metal electrodes and their potential for electrochemical control in devices. The porphyrin wires to be synthesised are conjugated, stiff and contain sites where charge can be localised. Other key attributes include lengths greater than 10 nm, remarkable stability, their ability to bind a wide range of metal ions and their capacity to be tuned with electrochemistry or photochemistry. It is expected that their attributes will allow them to conduct electrons over long distances. Their redox activity and ability to support pendent molecular groups will in turn provide avenues for current rectification, switching or charge storage. The investigations of the electrical properties of these porphyrin wires will require us to wire-up single molecules. This is clearly a big experimental challenge but the Liverpool group has recently developed new techniques using the scanning tunnelling microscope which makes this procedure more straightforward and reliable. These techniques will provide robust chemical contact of the single porphyrin molecules at both ends to metallic contacts. The role of the molecule/metal contact remains one of the most poorly understood and yet extremely important aspects of single molecule electronics. We will systematically investigate these contact effects through the use of several differing chemical groups for binding to the metal electrodes and complementary determination of the lineup of energy levels between the metal and the molecule. Although most of the electrical characterisation will be performed with two metal contacts at either end of the wire, in the later stages of the project a scanning probe contact will be introduced which can be scanned along the length of the wire probing electrical properties along the wire. The final goals of the project are to produce a series of novel porphyrin molecular wires and to have defined and understood electron transport across them down to the single molecule level and in different environments including UHV and electrolyte. Being able to probe the key variables (temperature, environment, oxidation state, metal atom, molecule stiffness, contact chemistry) for one molecular system will provide a systematic approach for formulating detailed mechanisms. In particular, the limiting roles of contact chemistries and non-ideal charge transport (inelastic scattering) processes will be defined. The ideal porphyrin molecular wire would support high currents and we will assess how closely this goal (quantum conductance limit) can be approached. We will also have evaluated the ability of these molecules to act as active molecular wires through the placement of redox addressable groups along their length.


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Description State of the art measurements have been made on porphyrin single molecule wires and understanding has been achieved of long range charge transport in these wires.
Exploitation Route This has stimulated further research and understanding of charge transport in molecular junctions.
Sectors Chemicals

Description This grant has provided new insights into long range charge transport through oligoyne molecular wires.
First Year Of Impact 2007
Description Danish Technical University 
Organisation Technical University of Denmark
Department Department of Photonics Engineering
Country Denmark 
Sector Academic/University 
PI Contribution Collaboration in molecular electronics (theory) with Prof. Ulstrup group.
Collaborator Contribution Collaboration in molecular electronics (experiment)
Impact Scientific publications, see publication list.
Description Univeristy of Zaragoza 
Organisation University of Zaragoza
Department Department of Chemistry
Country Spain 
Sector Academic/University 
PI Contribution Bilateral collaboration with Zaragoza University (Spain) on molecular electronics, LB films, single molecule electronics and electrochemistry.
Collaborator Contribution Bilateral collaboration with Zaragoza University (Spain) on molecular electronics, LB films, single molecule electronics and electrochemistry.
Impact See publications attributed.
Start Year 2007
Description University of Oxford 
Organisation University of Oxford
Department Physical and Theoretical Chemistry Laboratory
Country United Kingdom 
Sector Academic/University 
PI Contribution Collaboration on porphyrin nanoelectronics (measurements).
Collaborator Contribution Collaboration on porphyrin nanoelectronics (synthesis).
Impact Publications as listed.
Start Year 2006