Bipolar copoly(aryl ether) containing distyrylbenzene, triphenylamine, and 1,2,4-triazole moieties: Synthesis and optoelectronic properties

Abstract

A novel copoly(aryl ether) (P1) consisting of alternate emitting segments (distyrylbenzene) and a bipolar moiety composed of directly linked electron-transporting aromatic 1,2,4-triazole and hole-transporting triphenylamine was synthesized. The copoly(aryl ether) is readily soluble in common organic solvents and exhibit good thermal stability with thermal decomposition temperature above 450 °C. The emission and the photoluminescence quantum yield of the copolymer are dominated by the emitting segments (distyrylbenzene) with longer emissive wavelength. Electron affinity of P1 is evidently enhanced after introducing the isolated bipolar unit, as confirmed by the lowered lowest unoccupied molecular orbital level (-2.77 eV) relative to P0 without bipolar unit (-2.34 eV). This results in improved emission efficiency of its polymer light-emitting diode (indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)/P1/LiF/Ca/Al) due to more balanced charges injection and transport. Blending P1 with poly(9,9-dihexylfluorene) (PF) further improves the efficiency of the device; the best performance was obtained for PF/P1 = 20/0.8 (w/w) with maximum luminance and maximum luminance efficiency being significantly enhanced to 3260 cd/m2 and 1.08 cd/A, respectively, from 380 cd/m2 and 0.009 cd/A of P1-based device. These results demonstrate that the bipolar moiety can be used to enhance charges injection and transport of electroluminescent polymers. © 2011 Wiley Periodicals, Inc.