Facile synthetic route to a novel electroluminescent polymer-poly(p-phenylenevinylene) containing a fully conjugated aromatic oxadiazole side chain

Herein we report a facile synthetic route to a new conjugated polymer, poly{2-[5'-(2 "-octyloxy)phenyl)-1',3',4'-oxadiazole-2'-yl]-1,4-phenylenevinylene)}(OPO-PPV), in which a in which a high-electron-affinity aromatic oxadiazole moiety is attached on the PPV backbone as side chain. It is demonstrated that OPO-PPV is a new polymeric material with balanced charge injection for the application as emissive material in single-layer light-emitting diodes (LEDs). The present synthesis of OPO-PPV reveals a promising approach to balance the charge injection between electrons and holes into electroluminescent layers in polymer LEDs by controlling the intrinsic properties of light-emitting materials. The NMR ((13)C and (1)H) spectra of OPO-PPV demonstrate a well-defined structure in the polymer. The polymer exhibits good thermal stability (stable up to 368 degrees C in nitrogen) and high glass-transition temperature (170 degrees C). Both the absorption and photoluminescence spectra of the polymer have been studied. Cyclic voltammetry (CV) has been employed to estimate the highest occupied and lowest unoccupied molecular orbital energy levels of OPO-PPV. A comparison of the electrochemical characteristics with that of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is also discussed. A single-layer LED device ITO/OPO-PPV/Al is successfully fabricated. The device emits visible yellow-orange light above the bias voltage of 4.0 V under ambient conditions.