Silicon-Containing Organic Conjugated Materials for Light Emitting Diodes

Abstract

This thesis contains a study of polymer light emitting diodes (PLEDs) for commercial use within blue organic light-emitting diode (OLED) display technologies. The introduction chapter outlines the aims and synthetic strategies / targets employed during the research and gives background information as to the historical development of OLEDs and PLEDs. The first chapter of research involves the synthesis of several alternating co-polymers of dibenzosilole (a previously reported monomer used in light emitting devices), along with the prerequisite monomers. These co-polymers have been fully characterised and their optoelectronic properties evaluated. The energy levels of the co-polymers (HOMO / LUMO) were measured, then compared with each other and used to establish correlations between these values and the use of co-monomers and the polymer backbone linearity. By tuning the energy levels of conjugated polymers, it is possible to alter both the energy of the light emitted (and therefore the colour) and also improve the charge-injection balance within the OLED device, thereby improving lifetimes and performance. This research was primarily concerned with blue light-emission, therefore these energy level studies were conducted with a view to achieving blue light emission with the desired CIE coordinates and luminance. The novel co-polymers were used to fabricate several prototype OLED devices and the performance of these has been evaluated. The second chapter of research contains a study of several novel silicon-containing monomer structures, for incorporation into conjugated PLEDs. The first structure is a disilaanthracene derivative and the attempted synthesis of this monomer is reported. The other two monomers are based on spirosilabifluorene and the syntheses and full characterisations are reported. Attempts at the coupling of these monomers were made, using several different known coupling reactions including Suzuki, Stille and Kumada. The attempted coupling products were simple trimers, using 9,9-dioctylfluorene as a co-monomer. These were to be used in small molecule organic light-emitting diodes (SMOLEDs). The outcomes of these coupling reactions are described.