A Deep-Blue Electroluminescence from 2,5-Diphenyl-1,3,4-oxadiazole and Polyfluorene Copolymer End-capped with Triphenylamine

Abstract

An electron-transporting 2,5-bis(4-bromophenyl)-1,3,5-oxadiazole (OXD) was incorporated by copolymerization into polyfluorene (PF) end-capped with a 4-bromo-4',4"-dimethyltriphenylamine (TPA) main chains on the Yamamoto coupling method to improve the initial electroluminescence (EL) color stability against applied voltage and the device operation lifetime. The copolymer, PF/OXD-TPA, possessed a high molecular weight enough for film-forming ability and excellent solution-processability, that is, good solubility in common organic solvents such as toluene. An EL device fabricated using this copolymer as a polymeric emission layer allowed the generation of a strong deep-blue EL peaking at 424 nm with a comparatively high EL efficiency of 0.47 cd A -1, and its color was extremely stable against applied voltage within 527 V. The incorporation of OXD units into the PF-TPA system also improved the operation lifetime, although it is not a practical level for displays. The results are probably attributed to the great roles of the incorporated OXD units for disturbing the formation of fluorene excimer sites and for tuning the hole/electron mobility balance..

Deep-blue Electroluminescence of 9,9-Dialkyl-substituted Polyfluorene Copolymers Incorporating Diphenylsilane Units

“…This hypothesis is also supported from a previous result where a PF terminated with hole-transporting triphenylamine (TPA) units displays significantly improved color stability [8,15]. We also reported that the incorporation of controlled contents of electrontransporting 2,5-diphenyl-1,3,4-oxadiazole units into the TPA-terminated PF main chains through copolymerization allowed further improvement of the color stability [16]. The oxidative degradation also strongly depends on the device encapsulation techniques for complete air insulation.…”

Photo-optical properties of poly(oxadiazole-imide)s containing naphthalene rings

“…For such purpose, poly(1,3,4-oxadiazole)s are of great interest due to the electron-withdrawing character of the 1,3,4-oxadiazole ring that can facilitate the injection and transport of electrons. 11 We considered it interesting to synthesize two series of polyimides and copolyimides containing both oxadiazole and naphthalene units in the main chain, so that the resulting polymers have better thermal and thermooxitative stability and efficient photoluminescent and electron-transporting properties for future use in polymer lightemitting diodes. In this study, we investigated their thermal stability and photo-optical properties.…”

Copoly(1,3,4-oxadiazole-naphthylimide)s containing siloxane units in the main chain: synthesis and properties

“…In this regard, the 1,3,4-oxadiazole rings are promising chemical moieties for introduction into the polymer backbone or in the pendant structure due to the electron-withdrawing character of the 1,3,4-oxadiazole ring that can facilitate the injection and transport of electrons. 28 Therefore, the light-emitting ability of these polymers containing oxadiazole and naphthylimide chromophores was assessed on the basis of the photoluminescence spectra which were recorded for polymer solutions in NMP after excitation with UV light of different wavelengths.…”