1. Department of Organic Technology, Kaunas University of Technology, Radvilenu plentas 19, LT‐50254 Kaunas, Lithuania;2. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China;3. Macromolecular Chemistry, University of Wuppertal, Gau?stra?e 20, D‐42119, Wuppertal, Germany
Abstract:
New carbazole‐based copolymers, which contain various concentrations of 9‐alkyl‐3,6‐carbazole fragments in the main chain connected via alkylene spacers, have been synthesized by Ni(0)‐catalyzed Yamamoto‐type aryl‐aryl coupling reactions. Full characterization of the copolymer structure by NMR spectroscopy and elemental analysis is presented. These compounds represent amorphous materials of high thermal stability with glass transition temperatures of 151–162 °C and thermal decomposition starting at temperatures >390 °C. UV‐Vis absorption and photoluminescence emission of the copolymers confirmed that the effectively conjugated segment in the 3,6‐linked carbazole‐type copolymers is limited to dyads (dimeric units). However, copolymers with varying concentrations of the oligocarbazole chromophores demonstrate different charge injection and transport properties in multilayer light‐emitting diodes with the copolymers as the hole transport and Alq3 as the electroluminescent/electron transport layer. The device based on a copolymer composed of oligocarbazole blocks with an average length of around four carbazoles exhibited the best overall performance with a turn‐on voltage of 3.5 V, a maximal photometric efficiency of 4.1 cd · A?1 and maximum brightness of about 4 200 cd · m?2.
