Structural investigations of organic functional materials using NMR crystallography

Whewell, Tommy-Lee and Griffin, John (2024) Structural investigations of organic functional materials using NMR crystallography. PhD thesis, Lancaster University.

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Abstract

In Chapter 1, an introduction to organic functional materials within the scope of lithium-ion batteries and ferroelectricity is given. The importance of structural characterisation aiding future molecular design is discussed. The role of the lithium-ion battery in context of electric vehicles, and society as a whole, is further explored using futures thinking methods. In Chapter 2, a detailed summary of the key theory pertaining to NMR spectroscopy is presented alongside discussion of key experimental methods. Furthermore, the theory underpinning X-ray diffraction (XRD) and density functional theory (DFT) is given, along with discussion of the NMR crystallography method which encompasses the three techniques. In Chapter 3, the structures of organic anode materials in their pristine phase are characterised using NMR crystallography. A systematic study of DFT geometry optimisation methods finds that very good agreement can be achieved between experimental and calculated NMR observables when all atomic positions are optimised in conjunction with the use of a semi-empirical dispersion correction scheme. In Chapter 4, the reduced phases of organic anode materials are studied using a modified chemical lithiation methodology, found here to produce high purity samples. Through multinuclear NMR studies and random structure searching DFT methods, insights are gained into the structure of reduced organic anode materials where existing data from XRD is absent. In Chapter 5, the structural changes that occur in a model organic ferroelectric material, phenazine chloranilic acid, are characterised by NMR crystallography. Use of isotopic enrichment and variable temperature NMR methods enable information to be gained on low temperature ferroelectric phases, with DFT calculations on three dimensional superstructures shedding light on structures that exist outside of the temperature range of experimental methods. In Chapter 6, the conclusions from Chapters 3, 4 and 5 are presented aside suggestions for future work relating to these materials and methods.