Abstract
In recent years there has been a significant shift in the focus of research in the field of photophysics from the established paradigm of 4d and 5d metal complexes towards the more sustainable and earth-abundant 3d metals. The former display a variety of photoactive properties but utilise rare and expensive metal sources, the extraction and refinement of which are environmentally unsustainable. In pursuit of a more sustainable route to similar photoactive properties the use of iron (II) and cobalt (III) metal centres are attractive options. Within this thesis the preparation, characterisation and investigation of photophysical properties of several iron(II) and cobalt(III) octahedral complexes are reported. The first series of prepared complexes consist of homoleptic hexa-N-donor iron (II) complexes, using reference 2,2’:6’,2’’-terpyridine, 2,6-bis(1-ethyl-1,2,3-triazol-4-yl)pyridine, 2,6-bis(1-phenyl-1,2,3-triazol-4-yl)pyridine and 6-(1-phenyl-1,2,3-triazol-4-yl)-2,2’-bipyridine ligands, prepared from established synthetic routes, which exhibit relatively long-lived 5MC states, with potential use for low-cost photocatalysis. The second series of complexes is comprised of homoleptic N-heterocyclic carbene iron(II) complexes with varying levels of extension to the ligand π-system from two annulation sites, using reference 1,1’-(pyridine-2,6-bis(3-methyl-imidazolium)), 2,2’-(pyridine-2,6-bis(imidazo[1,5-a]pyridinium)), 2,2’-(pyridine-2,6-bis(imidazo[5,1-a]isoquinolinium)) and 1,1’-(pyridine-2,6-bis(3-methyl-naptho[2,3-d]imidazolium)) ligands. Synthetic routes for the preparation of the π-extended ligands are established. After complexation, the extension from one annulation site increases the light harvesting ability of the prepared complexes, red-shifting absorbance features, and extension of the other renders the 3MLCT state as the lowest energy excited state, similar to the established 4d and 5d metals, showing a potential route to improved photoactive ability for iron(II) complexes. Finally, the third series of complexes consists of homoleptic N-heterocyclic carbene cobalt(III) complexes using the same π-extended ligands are the iron (II) series. These ligands destabilise 3MC states of the cobalt(III) complexes, reducing the HOMO-LUMO gap and thus increasing the light-harvesting ability of the complexes, an issue that has made cobalt significantly less prevalent in the pursuit of sustainable photoactive properties.
| Date of Award | 3 Feb 2026 |
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| Original language | English |
| Supervisor | David Cooke (Main Supervisor) |