Structural characterization and luminescent properties of poly(p-phenylene vinylene) and poly(ethylene glycol) blends

The luminescent properties of poly(p-phenylenevinylene) (PPV) blending with poly(ethylene glycol) (PEG) were investigated in terms of their structural formation during sample preparation. The blended systems were prepared from an aqueous solution of water-soluble poly(xylylene tetrahydrothiophenium chloride) (PPV precursor) mixed with PEG, followed by heat treatment to remove the tetrahydrothiophene groups from the PPV precursor. Structural analysis showed that PEG could react with PPV precursor to form C-O-C linkage and carbonyl groups in PPV chains, interrupting their conjugated length as suggested by their Infrared, Raman and UV/vis spectroscopes. Wide angle X-ray scattering (WAXS) of blended systems also showed that PPV in blends had less packing. As to luminescent properties, the UV/vis and photoluminescent (PL) spectra show that the energy gap needed to produce the excitons increased along with the increase of PL intensity when PPV was blended with PEG. Similar results were also found for the EL properties of ITO/polyblends/Al devices. The EL light emission from blends was blue-shifted (compared to PPV) with a rather low threshold electric field strength. The EL performance of polyblends was better than that of pure PPV. Among them, the PPV-50PEG showed the highest EL intensity. The improved EL efficiency was attributed to the dilution effect, interrupted conjugated length, and lower packing of PPV chains.