Novel Polyfluorene Based Copolymers for Optoelectronic Applications

The interplay between the chemical structure of pi – conjugated polymers or oligomers and their macroscopic optical or electro-optical properties is complex in nature and not fully understood at the moment. It is crucial to design novel materials at the molecular level to tune the electronic properties and to improve the performance of devices made of these materials. Moreover, the nature of impurities and defects has also attracted great attention because of their remarkable influence on device performance.
Therefore, the first part of this thesis (chapter 2) deals with the origin of unwanted lower energy emissions in polyfluorenes. There is solid evidence that the formation of green PL/EL bands is not only caused by the formation of keto defects. To get a better insight into the degradation-based lower energy emission bands of polyfluorenes, novel polymeric model systems containing a certain amount of alkylidene “defects” incorporated into the main chain have been synthesized. Optical characterization is presented which implies that the green emission component observed preferably in electroluminescence can be addressed to additional defect structures besides the keto defect.

The second part of this work deals with the synthesis and characterization of electrophosphorescent copolymers. The syntheses of triplet emitters which are suitable as monomers for the preparation of electrophosphorescent polymers are described. Hereby, triplet emitters based on Pt(II)-salen complexes were synthesized and tested in OLEDs. In this first case the emitting layer (as blend) was solution-processed by mixing the dye as dopant into a polymeric host. The main target was to incorporate the triplet emitter into the main chain of a conjugated polymer (polyfluorene). This strategy should avoid morphological problems like phase separation. These (co)polymers were then tested as light emitting materials in phosphorescent OLEDs.
Chapter 3. also describes the synthesis of novel host materials with the aim of realizing improved device lifetimes. Consequently these results are adopted onto the synthesis of main-chain electrophosphorescent copolymers.