Accelerated degradation studies of MEH-PPV

MEH-PPV, which normally has a reddish color, is well known to show photobleaching problems. The photobleaching can be greatly accelerated by exposure to laser light while in air. For example, shining 457 mn light of relatively low intensity (0.06 W/cm{sup 2}) on the MEH-PPV causes the photoluminescence to decrease by a factor of two within a few seconds of exposure, and to show a nearly complete bleaching of the material within 30 minutes. The degradation rate is strongly influenced by laser power, sample thickness, oxygen exposure during preparation and spinning, as well as the oxygen environment during the measurement. The photobleach is indicative of one class of degradation mechanisms limiting the usefulness of PPV based polymers in electroluminescent devices. MEH-PPV which was spin coated in a nitrogen environment and measured in vacuum showed no measurable photo-chemical degradation for measuring times of up to several hours. A dramatic decrease in PL intensity was observed, however, in the presence of oxygen, as well as in samples spin coated in air, but measured in vacuum. We present data on the PL of MEH-PPV, as a function of oxygen concentration.