Copolyfluorenes containing pendant bipolar carbazole and 1,2,4-triazole groups: Synthesis, characterization, and optoelectronic applications

Abstract

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/m2 and 0.29 cd/A of MEH-PPV-only device to 15,690 cd/m2 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. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011