Synthesis, characterization, and electro-optical properties or a soluble conjugated polymer containing an oxadiazole unit in the main chain

A novel copolymer, poly{[2,5-diphenylene-1,3,4-oxadiazole-vinylene]-alt-[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]}(MEH-OPPV) containing a high-electron-affinity unit of aromatic oxadiazole in the main chain is synthesized through the Wittig condensation reaction. The obtained copolymer is easily soluble in conventional organic solvents. The structure of the copolymer was characterized by Fourier transform infrared, H-1 nuclear magnetic resonance, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and ultraviolet-visible and photoluminescence spectroscopy. The TGA result indicates that the copolymer has very high thermal stability (stable up to 310degreesC in nitrogen), while DSC investigation demonstrates that the glass transition temperature (T-g) is 143degreesC, which might be a merit for the long-life operation of light-emitting devices. The absorption spectrum of film sample of the copolymer reveals two peaks at 310 and 370 nm, respectively, and the edge absorption corresponds to a band gap of 2.46 eV. A single-layer light-emitting diode device ITO/MEH-OPPV/Al is successfully fabricated. The device emits visible yellowish-green light above the bias voltage of 4.0 V under ambient condition. (C) 2003 Wiley Periodicals, Inc.