Halogen precursor route to poly[(2,3-diphenyl-p-phenylene)vinylene] (DP-PPV): Synthesis, photoluminescence, electroluminescence, and photoconductivity

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 degrees C, and full conversion could be achieved at 170-250 degrees 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 FL, 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/Alq(3)/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 Alq(3) layer. These observations suggest that Alq(3) enhances the injection of electrons and also participates in the recombination process.