Understanding chromotropic materials with combined insitu Neutron Diffraction and Raman Spectroscopy

Dugmore, Sarah Kathryn

Abstract

In recent years, in many fields of scientific research, the multi-technique approach has grown into a robust method for the experimental characterisation of complex materials. The combination of diffraction, spectroscopy and other non-destructive techniques is nowadays seen as fundamental in order to understand in full the structure-properties relationship of functional materials for technological applications, especially when different techniques can be applied in situ to the same sample.

This thesis covers the technical development and testing of a new sample-environment equipment devoted at performing simultaneous in situ Raman scattering and Neutron diffraction measurements on the single crystal neutron diffractometer SXD at ISIS Neutron and Muon Facility in Harwell. This work reports the improvements to the equipment design, as well as examples of applications of the combined techniques to the study of two classes of chromotropic compounds: i) organic photo- and thermochromic materials, and ii) spin crossover complexes.

The organic chromic materials are Salicylaldehyde Aniline (SA) derivatives, a class of compounds that demonstrate photochromism and/or thermochromism via an enol to keto tautomerisation. Along with an investigation into SA derivates already known, two new SA derivates, one thermochromic and one photochromic, were structurally investigated for the first time. We identified a relationship between the dihedral angle between the two benzyl rings and the time and ease of conversion between the enol and keto states for the photochromic compounds. For the thermochromic compounds it was identified that there is a significant contribution to the chromotropism from the fluorescence displayed at low temperatures.

The Spin Crossover (SCO) complexes are metal-organic compounds that demonstrate chromotropism by effect of a change in the spin distribution of unpaired electrons in the transition metal atom, that can be induced by temperature change, light irradiation, or pressure. The investigation into SCO complexes lead to an expansion on the structural study of Ni(cyclam)I2, a thermochromic SCO, as well as the structural identification of a phase transition in the SCO precursor material Co(PF6) · 6H2O that was not identified before.

For the complete characterisation of the materials in this thesis, along with Raman scattering and Neutron diffraction other experimental techniques were also used: Single Crystal X-ray Diffraction (SCXRD), Infra-Red (IR) spectroscopy, NMR (1H and 13C), DSC and Inelastic Neutron Scattering (INS), as well as DFT calculations.

Citation

Dugmore, S. K. Understanding chromotropic materials with combined insitu Neutron Diffraction and Raman Spectroscopy. (Thesis). Keele University. Retrieved from https://keele-repository.worktribe.com/output/1012545

• Thesis Type: Thesis
• Deposit Date: Dec 5, 2024
• Publicly Available Date: Dec 19, 2024
• Public URL: https://keele-repository.worktribe.com/output/1012545
• Award Date: 2024-12