Time resolved spectroscopy of 21st century materials

Otaif, Haleema 2023. Time resolved spectroscopy of 21st century materials. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Spectroscopy is an important tool for chemists, that is widely used for characterizing novel materials and determining their physical and chemical properties through the analysis of their interactions with electromagnetic radiation. Conventional optical spectroscopic techniques, such as steady-state absorption and emission, can provide useful information about the electronic structure, molecular geometry, and functional groups of molecules in a sample, and allow chemists to identify the chemical composition and properties of many photostable compounds. However, these techniques are limited in providing information on reaction intermediates, excited states, and reaction dynamics. Therefore, transient spectroscopic techniques can be used to monitor the dynamics of excited states and observe how they decay back to the ground state, making it possible to obtain information on the energy, lifetime and nature of the excited states, and how external factors, such as temperature, influence their behaviour. In this thesis, a combination of steady-state and transient spectroscopic techniques, along with computational chemistry methods, are used to investigate and characterize a variety of novel luminescent organic and inorganic compounds. Firstly, I analyze the spectroscopic properties of a range of new cyclometalated IrIII complexes, varying in main ligand structure, ancillary ligands, or attached substitution groups, synthesized by the Pope group at Cardiff University. It was found that the photophysical properties of the complexes were highly tunable through modifications to their molecular structure. Using the combination of spectroscopy and computational methodologies this thesis highlights the development of a photocharacterisation library of over 30 heteroleptic iridium complexes, that displays relationships between photophysical properties and ligand design, ultimately used to design new iridium complexes that emit in the deep-red and near-IR regions. Secondly, the same analysis methodology was used to study photophysical properties of an N-substituted naphthalimide dyad and its thionated variants, supplied by Anna Wright from the Yi-Lin group at Cardiff University. These compounds demonstrate different types of emission, such as fluorescence, phosphorescence and thermally activated delayed fluorescence (TADF). Thionation of the carbonyl groups in these dyads has a significant effect on the singlet excited states responsible for the photochemical properties of these species which exhibit quenching of the prompt fluorescence, but the thionation does not appear to significantly change the triplet state. The analysis techniques provide a good insight into the effect of structure geometry, temperature, and solvent on the electronic character of these organic compounds. Finally, I describe the development of the transient absorption spectrofluorometer for highly sensitive fluorescence polarization measurements. The instrument was used to investigate the emission polarization of new dye-doped polymers and to examine the binding interactions between colistin and two strains of E. coli. The results show that the modifications of the spectrofluorometer is a cost-effective, and accurate tool for exploring fluorescence polarization and binding interactions in both biological and chemical systems.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Date of First Compliant Deposit:	18 January 2024
Last Modified:	18 Jan 2024 16:01
URI:	https://orca.cardiff.ac.uk/id/eprint/165651

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