Copoly(p-phenylene)s containing bipolar triphenylamine and 1,2,4-triazole groups: Synthesis, optoelectronic properties, and applications

Two novel copoly(p-phenylene)s (P1-P2) containing bipolar groups (12.8 and 6.8 mol %, respectively), directly linked hole transporting triphenylamine and electron transporting aromatic 1,2,4-triazole, were synthesized to enhance electroluminescence (EL) of poly(p-phenylene vinylene) (PPV) derivatives. The bipolar groups not only enhance thermal stability but also promote electron affinity and hole affinity of the resulting copoly(p-phenylene)s. Blending the bipolar copoly-(p-phenylene)s (P1-P2) with PPV derivatives (d6-PPV) as an emitting layer effectively improve the emission efficiency of its electroluminescent devices [indium tin oxide (ITO)/poly(3,4- ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/polymer blend/Ca (50 nm)/Al (100 nm)]. The maximum luminance and maximum luminance efficiency were significantly enhanced from 310 cd m^-2 and 0.03 cd A ^-1 (d6-PPV-based device) to 1450 cd m^-2 and 0.20 cd A ^-1 (blend device with d6-PPV/P1 = 96/4 containing ~0.5 wt % of bipolar groups), respectively. Our results demonstrate the efficacy of the copoly(p-phenylene)s with bipolar groups in enhancing EL of PPV derivatives.