Supramolecular Nanorings for Exploring Quantum Interference

Lead Research Organisation: University of Liverpool
Department Name: Chemistry


Young's famous double-slit experiment of 1803 demonstrated that light behaves as a wave. The light emerging from the slits has a characteristic intensity pattern originating from constructive and destructive interference. Later it was found that when single particles (photons or even molecules) pass through a double slit they produce similar interference patterns; this experiment became the key piece of evidence for wave-particle duality.

A Mach-Zender interferometer is similar to Young's double-slit setup, except that light is split into two routes using mirrors. When the light is recombined, constructive or destructive interference occurs, depending on the difference in the phase of the light from the two routes. Subtle differences in the path-length, or refractive index, can easily be detected, because they determine the phase difference, and thus they control the interference.

This project aims to synthesise and test a "molecular Mach-Zender interferometer" consisting of a molecule with two charge-transport paths; interference between the two transmission channels controls whether the whole system is conductive (in phase) or non-conductive (out of phase). Thus these molecules are expected to be sensitive to magnetic or electric fields which can change the relative phases of the two channels. Furthermore quantum interference effects tend to produce sharp changes in transmission with electron energy, which can result in strong thermoelectric effects. This project is concerned with exploring fundamental principles, but in the long term, this research has the potential to generate commercially disruptive technologies, such as thermoelectric devices for scavenging thermal energy, and transistors with reduced power requirements, abrupt switching and small footprints.

This project if a thoroughly integrated collaboration of three research groups focusing on (1) Oxford: design and synthesis of molecular structures, (2) Liverpool: testing of single molecule conductance and thermopower, and (3) Lancaster: theory and computational simulation, to guide the interpretation of the experimental data, and the design of new molecular structures.

At present there exists a no-man's land between the 15-nm length scale accessible to top-down technologies, such as electron-beam lithography, and bottom-up technologies such as chemical synthesis. The molecules investigated in this project are 3 nm across, but can be increased in size up to around 10 nm. This project is therefore a significant step towards bridging this crucial technology-scale gap, at the limit of Moore's law.


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Description We have achieved enhanced understanding of charge flow through porphyrin molecular wires. This includes the unique discovery of bias voltage driven conductance increases with length in porphyrin tapes. We have detected mechanochemical atropisomerization within an STM break junction containing porphyrin molecular wires. We have extended single molecule conductance measurements to supra-molecular assemblies including porphyrin nano-rings synthesised by our collaborators. Our collaborating partner has also demonstrated quantum interference in porphyrin nanorings through EPR measurements. In addition, we have studied quantum interference effects in other conjugated systems, such as how cross-conjugation increases the conductance of meta-connected fluorenones and the unusual length dependence of the conductance in cumulene molecular wires.
Exploitation Route This project is providing insights into quantum interference which may be valuable in the field of nano-electronic devices and molecular electronics.
Sectors Chemicals,Education,Electronics

Description University of Madrid 
Organisation Autonomous University of Madrid
Country Spain 
Sector Academic/University 
PI Contribution Collaboration in single molecule electronics
Collaborator Contribution Collaboration in single molecule electronics
Impact Publications in preparation.
Start Year 2015
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