Copolymers by radical polymerization containing phosphorescent iridium(III) complexes

Introduction Phosphorescent transition-metal complexes feature potential to improve the efficiency of organic light emitting devices (OLEDs) significantly. While pure fluorescent emitters can not exceed a maximum efficiency of 25%, given by spin statistics, phosphorescent complexes can harvest triplet as well as singlet excitons, due to strong spin-orbit coupling, approaching internal quantum efficiencies up to 100%. Especially phosphorescent iridium(III) complexes, which exhibit the possibility to tune optical and electrical properties by varying the attached ligands, are interesting candidates to build up phosphorescent multi-color devices. While OLEDs fabricated by vapor-deposition of small and thermal stable molecules typically show the best performance, device fabrication by solution processing techniques such as inkjet printing, spin coating, etc. inhere great interest, because of their rather low costs and the possibility to handle even large areas rather easily. In contrast to vapor-deposition, techniques based on the processing of solutions show in principle no limitations concerning the molar mass of the materials used or the application of also charged species. In relation to solution processing, polymeric materials are of special interest, with respect to their film forming properties and flexibility. The combined use of suited polymeric host materials together with small emitter molecules as well as further charge carrier molecules, blended therein, find wide application in single-layer devices. However, blend systems inhere the possibility of undesired phase separation, aggregation or crystallization. Therefore, copolymers combining the different functions are object of intense research. Copolymers, conjugated as well as non-conjugated, containing hole transport (HT) molecules, electron transport (ET) molecules and neutral phosphorescent iridium(III) complexes, obtained by Suzuki-, Yamatocoupling, free radical, controlled radical and ring opening polymerization as well as ring opening metathesis, have been reported. In this contribution, we describe the synthesis and characterization of a methacrylate functionalized phosphorescent iridium(III)-complex exhibiting orange emission as well as its use in different copolymerizations and the investigation of the obtained polymers.