Hole-transporting polymers containing carbazol-3,9-diyl and 1,4-phenylene fragments in the main chain

New carbazole-based polymers, which contain various content of electro-active fragments in the main chain connected via alkylene spacers, have been synthesized by Ni(0)-catalyzed Yamamoto-type aryl-aryl coupling reactions. These compounds represent amorphous materials of high thermal stability with glass-transition temperatures of 139-151 degrees C and thermal decomposition starting at temperatures above 400 degrees C. UV-vis absorption and photoluminescence emission spectra of the materials confirmed that the conjugated segments in the macromolecules are rather short. However, the polymers with varying content of the electro-active chromophores demonstrate different charge injection and transport properties in multilayer light emitting diodes with the polymers as the hole transport and tris(8-quinolinato)aluminium (Alq(3)) as the electroluminescent/electron transport layer. The device based on the polymer containing bicarbazole segments in the main chain exhibits the best overall performance (turn-on voltage: 4V; maximum photometric efficiency: 2.6cd/A; maximum brightness: approximately 2200cd/m(2)). (C) 2008 Elsevier B.V. All rights reserved.