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Abstract

In this work, novel materials for organic light-emitting diodes (OLEDs) have been synthesized and characterized. In the first part, the development of new host materials for blue phosphorescent OLEDs is described. These compounds have to fulfill three major requirements: they should possess good charge-transport properties, a stable amorphous phase at operation temperature and, most importantly, their triplet energy E(T1 S0) has to exceed the triplet energy of the emitter. Therefore the conjugated π–system has to be confined. Two different approaches have been pursued: First, the examination of dibenzofurofurans as a novel moiety with a large conjugated π–system, yet high (calculated) triplet energy. Secondly, tetraphenylene was used as a novel molecular design element to connect moieties known for their good charge-transporting properties with little conjugation between these fragments. The properties of all potential target molecules have first been predicted by DFT-calculations. For the most promising candidates, synthetic routes have been developed and executed. In the course of this work, seven novel dibenzofurofuran-based host materials were synthesized, revealing a surprisingly high reactivity of this class of compounds. Furthermore, five new carbazole- and dibenzofuran-annelated tetraphenylenes have been obtained by dimerization of the corresponding biphenylenes. All final products were characterized using UV/Vis-, fluorescence- and phosphorescence spectroscopy, cyclic voltammetry and differential scanning calorimetry. In this way, the most important parameters of a host material, transport levels (ionization potential, electron affinity), triplet energy and glass-transition temperature were determined. Almost all of the obtained compounds show a high glass-transition temperature of Tg > 100°C, transport levels close to those of other common OLED materials and a high triplet energy of E(T1 S0) > 2.7 eV. The most promising candidates were applied in OLED devices, with one of the tetraphenylene derivatives showing an exceptionally high efficency of almost 13%. In the second part of this work, a known emitter was synthetically modified to enable its use in solution-processed OLEDs. Three new, highly soluble emitters have been obtained, showing thermally activated delayed fluorescence (TADF) with high luminescent quantum efficencies (φ > 80%) and short excited-state lifetimes (τ > 4 µs). Moreover, five new host materials for this class of emitters were synthezied and characterized.