Icosahedral Boron Clusters: Building Blocks In Luminescent Materials
- Author(s): Kirlikovali, Kent Ozan
- Advisor(s): Spokoyny, Alexander M
- et al.
This dissertation describes the development of unique ligand scaffolds incorporating icosahedral carboranes, a robust group of organomimetic clusters that provide a variety of tunable frameworks not attainable with standard aromatic ligands, for use in luminescent transition metal complexes. Specifically, we have targeted blue phosphorescent Ir(III)- and Pt(II)-based emitters in the context of organic light-emitting diode (OLED) applications. OLEDs incorporating these types of emitters have achieved remarkable efficiencies in recent years, leading to the development of thinner and less energy-intensive television screens, mobile phone displays, and solid-state lighting sources. In order to realize the full potential of OLED-based devices on a global scale, critical issues related to efficiency and lifetime of blue OLEDs must be addressed.
Chapter One provides a brief history of lighting technology and the current status of OLED technology. An overview of blue phosphorescent Ir(III)- and Pt(II)-based emitters is discussed, including key design parameters and current challenges associated with this class of emitters. Lastly, a background on boron cluster chemistry is provided.
Chapter Two describes a new class of robust and highly luminescent bis(heteroleptic) Ir(III) complexes containing weakly coordinating nido-carboranyl substituents. These ligands associate with the cationic Ir(III) center through primarily electrostatic interactions. Importantly, the observed quantum yields for these complexes correspond to a 10-fold increase compared to those of previously reported Ir(III) complexes with carboranyl-based ligands featuring covalent interactions between the cluster and the Ir(III) center.
Chapter Three introduces a dianionic, strong field ancillary ligand framework based on 1,1′-bis-o-carborane (bc). A blue phosphorescent Pt(II) complex featuring the bc ligand is studied. The bc ligand remains photophysically innocent in all visible transitions, and it provides sufficient steric bulk to preclude parasitic intermolecular Pt(II)⋯Pt(II) interactions.
Chapter Four details the synthesis of two isomeric Pt(II) complexes featuring the bc ligand. Control over the mode of chelation of the bc ligand to the Pt(II) center enables the fine-tuning of the electronic properties of the resulting Pt(II) complexes by virtue of vertex-differentiated coordination chemistry of carborane-based ligands.
Chapter Five presents current progress towards luminescent metal complexes featuring multidentate carborane-based ligand architectures. This class of ligands should result in more rigid metal complexes with improved emission efficiency and greater stability. Ultimately, this work presents potentially new avenues for designing efficient blue phosphorescent emitters through the use of tunable carborane-based ligand scaffolds.