Novel iridium complexes with polymer side-chains
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Novel iridium complexes with polymer side-chains Elisabeth Holder, Veronica Marin, Emine Tekin, Dmitry Kozodaev, Michael A. R. Meier, Bas G. G. Lohmeijer and Ulrich S. Schubert* Laboratory of Macromolecular Chemistry and Nanoscience, Eindhoven University of Technology and Dutch Polymer Institute (DPI), P.O. Box 513, 5600 MB Eindhoven, The Netherlands
ABSTRACT The focus of the presented research lies on the synthesis of novel charged iridium(III) compounds with potential applications in light-emitting electrochemical cells. The design involves iridium(III)-based materials with polymer side-chains leading to linear lightemitting polymer arrangements. To study the electro-optical properties of such light-emitting polymers conventional and combinatorial deposition methods are used. Straightforward screening approaches are introduced. The combinatorial efforts engage the processing via inkjet printing and the screening of the optical properties using plate reader technologies based on steady state UV-vis and fluorescence. Furthermore, the morphological properties are investigated using optical interferometry and atomic force microscopy (AFM). Overall it can be shown that novel materials can be deposited revealing high-quality thin films, which allow the screening of electro-optical features using combinatorial methods. Some initial local current density studies by AFM have also been performed to characterize the current injection and transport properties of the novel materials.
INTRODUCTION The synthesis and design of new materials is an important topic in current research due to the growing development of technological relevant applications. Electroluminescent materials have become progressively more interesting due to their potential applications in light-emitting diodes (LEDs) [1,2] and light-emitting electrochemical cells (LECs).[3] Both LEDs and LECs find use in displays and lighting applications but the work performed on LEDs is more mature compared to development performed on LECs. The working principle of the introduced devices is slightly different therefore different classes of iridium compounds were designed.[4] Neutral iridium compounds find applications in LEDs whereas charged compounds find use in LECs. One of the drawbacks in LECs is the rapid degradation on the electrode surface. Another observed feature in both devices is the aggregation of complexes leading to reduce device lifetimes. Some work carried out on ruthenium compounds showed that copolymerization or blending with polymers such as PMMA improved the device performance significantly.[5] Studying the electro-optical properties and the lifetime of potential material compositions is rather time consuming and the structure-property relationships need to be carefully evaluated in order to make a smart design of materials. Therefore a novel processing and screening approach is currently developed. Inkjet printing is being used to deposit test-pixels of the novel electroluminescent materials. Optical screening was carried out in solution and
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