Synthesis and characterization of a fluorene-quinoxaline copolymer for light-emitting applications.

A conjugated copolymer based on 9,9-dioctyl-fluorene and 2,3-bis(4-(hexyloxy)phenyl) quinoxaline has been synthesized by the palladium-catalyzed Suzuki coupling reaction. The synthesized polymer was soluble in common organic solvents such as chloroform, THF, and toluene and had good film properties. The polymer was analyzed by 1H-NMR spectroscopy, UV-vis spectroscopy, GPC, TGA, DSC, and cyclic voltammetry. It had very good thermal properties with high decomposition and glass transition temperatures, 420 degrees C and 159 degrees C respectively, and a low band gap of 2.51 eV. The polymer LEDs (ITO/PEDOT:PSS/polymer/LiF/Ca/Al) showed pure green light emission with maximum peaks at 502 nm and CIE coordinates of x = 0.28 and y = 0.55. The turn-on voltage of the polymer device was 7 V and the maximum brightness was 10.16 cd/m2 at 14 V. The maximum luminescence efficiency of the polymer was 0.0011 cd/A at 11 V.