Luminescent N-Heterocyclic Carbene Platinum(II) Alkyne Frameworks: Small Molecules, Excimers and Polymers

Abstract

This thesis work is focused on fundamental investigations into new classes of luminescent organometallic small molecules and polymers with potential applications in organic light emitting diodes (OLEDs). In the past few decades, extensive research has been carried out with transition metal complexes, especially because of their potential for a fourfold increase in energy conversion compared to organic molecules. The pursuit of high efficiency, in order to create sustainable display and lighting devices, drives the search for new materials to replace the inefficient incandescent light bulbs and the toxic mercury-based fluorescent tubes. Also, with smart phones and television displays and other digital devices, playing a crucial role in our daily lives, OLEDs are nowadays widely used. With increasing population, the global demand of electricity is rising, which can only be lowered by optimizing the energy consumption. The general demand for deep blue and white emissive materials is tremendously increasing. For an efficient full color display with good color purity, a pure blue emitter is essential. Transition metal complexes have been thoroughly investigated in the past few decades, covering the entire visible spectrum, showing efficiencies suitable for applications in OLEDs, excluding the deep blue region. Indeed, blue is essential for full color displays, not only as a standalone color, but also in the fabrication of white light devices. For a wide range of applications, such as sensing devices or medical device technologies, the near-infrared (NIR) region is also of great importance. In this context the focus has shifted towards the two edges of the visible spectrum, the high energy blue and the low energy NIR emission. In this work two different types of molecular systems are investigated. Firstly, the small molecule systems that emit in the deep blue and the NIR that are suitable for vapor deposition due to high thermal stability and the possibility of sublimation onto a substrate were investigated. Since, this technique is limited to the application on small areas due to the vacuum sublimation chamber, organometallic main-chain polymers were developed as another class of systems. They are a promising alternative to their small molecule analogues, due to the possibility of solution deposition. This technique allows to fabricate large area devices, analogous to inkjet printing. It would be of great importance for the production of large panel lighting substitutions on an industrial scale, to replace the inefficient incandescent light bulbs or the toxic mercury tubes. In this context, a new class of organometallic polymers that showed tunable emission properties at ambient temperature in solution was investigated.