Chemistry of open-shell correlated materials based on unsaturated hydrocarbons

This is a long-range basic research project that targets the synthesis of a new crystalline materials family whose chemical, electronic and magnetic properties will create opportunities in fundamental science. To date, such advances have mainly been made in inorganic materials. This project will extend that opportunity to materials where the electronically active component is an organic anion.

Our understanding of materials such as silicon and copper relies on a description of the electrons in which they do not interact strongly with each other. The electronic behaviour of materials in which the electrons do interact strongly, known as correlated materials, differs from such classical free electron materials. Correlated materials have been a fruitful source of new electronic and magnetic ground states and properties. This behaviour has overwhelmingly been observed in inorganic systems, because of the capability offered by inorganic solid state materials chemistry to position multiple distinct metal cations and thus predictably arrange spins, orbitals and charges. We have no such synthetic capability or crystal chemical understanding for organic correlated electron materials. The one example of success is the fulleride superconductors such as K3C60, where the underlying crystal chemistry is based on sphere packing that is directly analogous to well-studied inorganic systems, enabling extensive synthetic control and property design.

While currently offering an outstanding range of properties, all-inorganic systems are restricted to the atoms provided by the periodic table, whose crystal and electronic structures are controlled by the ionic size and orbital characteristics of those elements. If we could achieve similar general control of structures based on electronically active organic species, such as anions derived by reduction of unsaturated molecules studied here, the resulting structural and electronic properties would be determined by the molecular size, shape and electronic structure. In contrast to the inorganic ionic systems, these steric and electronic structures of the organic molecules that would be the building blocks of such materials are controllable by synthetic chemistry.

In two recent papers in Nature Chemistry, we have reported chemical synthesis approaches that produce crystalline salts of reduced unsaturated aromatic molecules and access new electronic states, including a candidate for the quantum spin liquid ground state in a three-dimensional pi-electron based material. This advance demonstrates the potential to create a family of tuneable crystalline organic electronic materials beyond the fullerides. The project will establish this family, allowing the positioning of electronically and sterically tuneable building blocks to control electronic, magnetic, optical and charge storage properties.

This will be achieved by developing the synthetic chemistry capability to produce crystalline materials from a broad range of unsaturated organic molecules. To generate materials of comparable compositional and structural complexity to the inorganic systems, we will apply and expand this chemistry to materials with multiple metal sites and with more than one molecular component. This will allow us to control extended electronic structure by positioning of and charge transfer between the molecular units to target geometrically frustrated magnetic lattices and mobile charges in quantum spin liquids as examples of the new electronic ground states this chemistry will enable. The compositions, charge states and structures of the resulting hydrocarbon salts will reveal the charge storage potential of this family of materials.

We will use informatics techniques to guide efficient exploration of the chemical space, and apply a range of structural, thermodynamic, spectroscopic, electronic and magnetic measurement techniques with our international collaborators to identify the new electronic states that arise.

The project will deliver understanding and capability in the synthesis and design of new crystalline organic materials based on reduced unsaturated hydrocarbons with currently unpredictable electronic, magnetic, optical and redox properties. The short-term impact will be on academic and industrial basic research.

Understanding of the design of advanced materials contributes broadly in the long-term to innovation across multiple high value industry sectors where our ability to control material structure and properties at the atomic and molecular level is essential to deliver advances in materials and resultant product functionality. It is also possible to identify potential long-term ramifications for specific technologies.New electronic ground states produce opportunities for information storage or processing technologies. For example, the new materials families are candidate quantum materials for ground states such as the quantum spin liquid (QSL). The excitations of exotic magnetic states such as fractional spinons in the QSL have been proposed as components of low-energy computation because they can be manipulated without charging. The entanglement of states in the QSL enables certain quantum computing architectures.The specific understanding and materials arising from insertion of electropositive metals into redox-active unsaturated organic molecules is relevant to the development of lightweight, recyclable high charge storage capacity battery cathodes.

The basic understanding emerging from the project could enable reduced energy use in computation and diversification towards organic materials, with associated environmental benefits. Society will benefit from two postdoctoral researchers trained in the synthesis, characterisation and design of a new generation of advanced materials, and equipped with an understanding of informatics methods.

Advances relevant to energy storage will be evaluated with battery materials developer PV3 and the Faraday Institution, for low-energy computing with the Energy Efficient ICT theme of the Royce Institute(where Liverpool are partners) and Colour Synthesis Solutions (also display technologies), and for quantum technology via the Innovate UK (iUK) KTN Special Interest Group. We will engage with UK industry through the Knowledge Centre for Materials Chemistry (KCMC) to realise the broader long-term impacts. KCMC fosters collaboration with chemistry-using industries and delivered £200M GVA to the UK economy in its first 5 years. The PI is a founding member of the KCMC Management Group. Relevant advances identified at monthly formal project meetings will be communicated to KCMC knowledge transfer staff, who will disseminate the information via their extensive network to the most appropriate industrial beneficiaries. This will raise industry awareness of the opportunities this new class of materials and the advances in capability required to access them present, and identify challenges unmet by current materials classes. KCMC will work with iUK, KTN and High Value Manufacturing Catapult staff to maximise exploitation of project advances.

Intellectual property will be protected by University of Liverpool Business Gateway. The project team have licensed two patents arising from basic research to UK industry.

Project advances will be disseminated by high profile publications including journals such as Nature and Science, where the team have a strong track record. We will engage with the Directed Assembly and Dial-a-Molecule EPSRC Grand Challenge networks to highlight project advances, as well as presenting at IOP, RSC and international meetings.

Project advances will be highlighted to policymakers and stakeholders beyond academia via KCMC events such as the 2016 "Materials for the Future" attended by over 80 senior industrialists and the CEO of iUK. We will engage the public through press releases and web-based dissemination such as the 2018 Science webinar at Curious 2018.