Ionic transition metal complexes containing iridium(III) for lighting applications

This PhD thesis concerns the synthesis of new ionic transition metal complexes based on iridium(III) complexes for applications in light-emitting electrochemical cells (LECs).
Chapter 1 gives a short introduction to the historical and chemical backgrounds of the element iridium and of LECs.
Chapter 2 shows the importance of the purity of the anion in the iridium(III) complexes on the performance of LEC devices.
Chapter 3 shows the influence of changing the size of the anion on the LEC performance and its direct influence on the mobility of the ions in thin films.
Chapter 4 describes the synthesis and characterization of iridium(III)-based blue emitters with high quantum efficiency.
Chapter 5 details the introduction of 2,2’:6’,2’’-terpyridine (tpy) ligands in the field of iridium(III) complexes. The pendant pyridine ring undergoes intramolecular face-to-face p-stacking interactions, similar to pendant phenyl rings of 2,2’-bipyridine (bpy) ligands. The NMR spectroscopic assignments of these iridium(III) complexes are shown. Through the extension of the p-conjugation of the ancillary ligand, the emission maximum of the complexes is shifted towards the red region of the visible spectrum.
Chapter 6 reports further tpy-based iridium(III) complexes and their performances in LEC devices.
Chapter 7 discusses the stereochemistry of the octahedral iridium(III) atom and shows trials towards multinuclear iridium compounds.
Chapter 8 concludes this PhD thesis and gives an outlook for further research efforts.
Summary and Outlook:
In this PhD thesis, a series of new iridium(III) complexes was successfully synthesized and characterized. Many of the complexes have been characterized by NMR spectroscopy, MS, EA and IR as well as by X-ray analysis. The hindered rotation of the pendant aromatic rings of the ancillary ligands was investigated using variable temperature NMR spectroscopy. In addition, many of the complexes were investigated in thin-film and/or LEC configuration.
Since the first report of an iridium-based light-emitting electrochemical cell, research efforts in this field have yielded many significant results. Starting from a yellow emission, the range of colours has been enlarged towards blue (452 nm) and deep-red (687 nm) with high colour purity. In addition, for LEC devices the lifetimes have been increased to many thousands of hours and the turn-on time has been shortened. There are still many goals to achieve in the near future before a product can become commercially viable. The combination of high efficiency, high brightness, long lifetime and short turn-on time in a LEC device is still a challenge. Complexes based on iridium are very useful models for investigating and improving the properties of iTMC based LEC devices. In future, the research should aim for more abundant elements, e.g. zinc or copper, to replace the core iridium atom, to be able to produce commercial LEC products over a long period of time.