Copolyfluorenes Containing Pendant Bipolar Carbazole and 1,2,4-Triazole Groups: Synthesis, Characterization, and Optoelectronic Applications

Three novel copolyfluorenes (P1-P3) containing pendant bipolar groups (2.5-7.7 mol %), directly linked hole-transporting carbazole and electron-transporting aromatic 1,2,4-triazole, were synthesized by the Suzuki coupling reaction and applied to enhance emission efficiency of polymer light-emitting diodes based on conventional MEH-PPV. The bipolar groups not only suppress undesirable green emission of polyfluorene under thermal annealing, but also promote electron- and hole-affinity of the resulting copolyfluorenes. Blending the bipolar copolyfluorenes with MEH-PPV results in significant enhancement of device performance [ITO/PEDOT:PSS/MEH-PPV+P1, P2 or P3/Ca(50 nm)/Al(100 nm)]. The maximum luminance and luminance efficiency were enhanced from 3230 cd/m(2) and 0.29 cd/A of MEH-PPV-only device to 15,690 cd/m(2) and 0.81 cd/A (blend device with MEH-PPV/P3 = 94/6 containing about 0.46 wt % of pendant bipolar residues), respectively. Our results demonstrate the efficacy of the bipolar copolyfluorenes in enhancing emission efficiency of MEH-PPV. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3928-3938, 2011