Development of Novel Iridium(III) Complexes for Light-Emitting Devices

  • Joshua Adams

Student thesis: Doctoral Thesis


Photochemistry and photophysics are omnipresent in the natural world, making them of great scientific interest. The reproduction and application of their processes in chemical, physical, biological, and medical technologies have emerged as areas of great interest. The forefront of current research lies in the development of highly efficient light-emitting devices, where increased efficiency translates to reduced energy consumption. This pursuit holds paramount importance in mitigating the climate crisis by curbing carbon emissions. Recent advancements in OLEDs and LEECs have demonstrated significantly more efficiency compared to traditional lighting methods.Amongst transition metal complexes, Ir(III) complexes emerge as the most promising candidates for photo- and electroluminescence. Tunability across the colour spectrum can be achieved by modifying their ligands. These complexes exhibit a remarkable array of photophysical properties, including the ability to modify emission characteristics via ligand manipulation, good kinetic and thermodynamic stability, and exceedingly high quantum yields.The primary objective of this thesis revolves around the advancement and exploration of light-emitting complexes through the synthesis of novel Ir(III) complexes, aiming to modulate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). This research work seeks to contribute to the development and progress of light-emitting devices, enriching our understanding of their properties, and open up new possibilities for a multitude of applications.This thesis presents the findings of my research in the development of Ir(III) complexes for light-emitting devices:Chapter 2 consists of the synthesis of heterodinuclear Ir(III)-Ru(II) complexes where the bridging ligand between the two metal centres is based on aryl-1,2,3-triazole ligands. The mononuclear counterparts were also synthesised. The photophysical properties of these complexes were investigated. It was revealed that two of the fluorinated multinuclear complexes were white light emitting. The reported complexes were tested for their photostability and were found to be photolabile. The photochemical properties were investigated for the heterodinuclear Ir(III)-Ru(II) complexes. The metal centres separated through photolysis resulting in a turning of the Ir(III) emission.Chapter 3 consists of the synthesis of a series of cyclometalated Ir(III) complexes designed to explore the high energy T1 states for Ir(III) complexes. The cyclometalating C^N ligand was selected to be 3, 5-Dimethylpyrazole phenyl whilst the N^N ancillary ligand was a series from 2,2’-bipyridyl (bpy)→ 2-(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine (pytz) → 4,4-bi-1,2,3-triazol-4-y (btz) and 2-(1-benzyl-1H-1,2,3-triazol-4-yl)-6-methylpyridine (m-pytz). The photophysical properties were investigated for these complexes. It was found that the btz and m-pytz complexes were readily accessing the 3MC states upon excitation. Computational studies confirm that the btz complex accesses the 3MC states, this was achieved through manipulation of the electronic properties of the complex. Whilst the m-pytz complex also accesses the 3MC states, this was performed through the ligand architecture, designed to increase bond lengths through steric hindrance.Chapter 4 consists of the synthesis of novel Ir 3+2+1 triazoles complexes based on the [Ir(N^N^N)(C^N)Cl]+ structure. The synthesis entails aryl-1,2,3-traizole ligands and archetypal pyridine-based ligands. The complexes were designed to explore new chemical space thus their photophysical properties were assessed. The C^N triazole based complex showed respectable photophysical properties, with a relative photoluminescent quantum yield (ϕ) of 9.1 % and lifetime (τ) of 1.7 μs. The N^N^N triazole based complexes had less impressive relative quantum yields (ϕ =
Date of Award20 Dec 2023
Original languageEnglish
SponsorsEngineering and Physical Sciences Research Council
SupervisorPaul Elliott (Main Supervisor), Paul Scattergood (Co-Supervisor) & Mark Heron (Co-Supervisor)

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