Halogen Precursor Route to Poly[(2,3-diphenyl-<i>p</i>-phenylene)vinylene] (DP-PPV): Synthesis, Photoluminescence, Electroluminescence, and Photoconductivity

Abstract

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.