We report measurements of photoluminescence from films of a soluble phenylenevinylene polymer that has prospective importance as the emissive material in light-emitting diodes. We show unambiguously that there is long-lived emission in this material due to excimers and estimate that the quantum yield for excimer formation is as high as 50%. Since excimers in this polymer largely decay nonradiatively at ambient temperature, their prominence serves to drastically reduce the possible efficiency of electroluminescent conjugated polymer devices.

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The electronic and structural properties of fulleride anions are of considerable interest due to the discovery of superconductivity in the alkali metal intercalated fullerides' and ferromagnetism in [TDAE][C,-~O].~ Reductions in symmetry of the fulleride anions, such as the expected Jahn-Teller (JT) distortion in the C60n-(n = 1-5) anions, are of particular interest due to the possible role of cooperative symmetry-breaking vibrations in electron-phonon mechanisms of superconductivity in the M3Cm phase^.^ However, relatively few examples of structurally well-characterized fulleride salts have been reported. Reed and coworkers have reported evidence for distortion of the Cm dianion in [PPN+]2[Cm2-]$ but at present there is no structural evidence for the JT distortion expected in the Cm monoanion.Among the increasing number of discrete fulleride salts that have been isolated and two single-crystal X-ray structures of Cm-salts8 have been reported; however, both structures exhibit disorder in the Cm monoanion. ~~~~ ~~~~ ~~~ (1) (a) Hebard, A. F.; Rossemsky, R. C,; Haddon, D. W.; Murphy, S. H.; Glarum, T. T. M.; Palstra, A. P.; Ramirez, A. P.; Kortan, A. R. Nature 1991, 350, 600. (b) Rosseinsky, M. J.; Ramirez, A. P.; Glarum, S. H.; Murphy, D. W.; Haddon, R. C.; Hebard, A. F.; Palstra, T. T. M.; Kortan, A. R.; Zahurak, S. M.; Makhija, A. V.

Thin films of poly[(2,3-diphenyl-p-phenylene)vinylene] (DP-PPV) have been prepared via a chlorine precursor route (CPR). This involves the polymerization of 1,4-bis(chloromethyl)-2,3-diphenylbenzene with 1.0 equiv of potassium tert-butoxide to give the chlorine precursor polymer of DP-PPV. The chlorine precursor was thermally converted at different temperatures to give DP-PPV with different degrees of conversion. The conversion process was monitored by in situ photoluminescent (PL) spectroscopy. The onset of conversion was about 150 °C, and full conversion could be achieved at 170−250 °C. The degree of conversion was a function of the heating temperature rather than the duration of heating. The fully converted DP-PPV showed lower photoconductivity and higher PL intensity than PPV. Although partially converted DP-PPV showed bright PL, we have not been able to observe its EL. The electroluminescence (EL) of the single layer ITO/DP-PPV/Mg and the bilayer ITO/DP-PPV/Alq3/Mg LED devices is also reported. A significant improvement in the quantum efficiency (up to 0.7% ph/el) and a reduction in the turn-on voltage of the device were found upon incorporation of the Alq3 layer. These observations suggest that Alq3 enhances the injection of electrons and also participates in the recombination process.