e light by interrupting conjugation in the polymer with nonconjugated units. Attachment of alkoxy side groups to the phenylene rings of the PPV enables red light production. A full-color polymer-based display requires pixellating the colors through the combination of different conducting polymers with varying band gaps. The color emitted from the blend will depend on the amount of voltage applied, which increases with the band gap. An alternative route would be to use white- light-emitting diodes to create a microcavity, the length of which determines the color of the emitted light. Apart from varying band gaps, polymer-based light-emitting diodes also face the challenge of increasing operating lifetimes to at least 20,000 hours to popularize commercial usage. When the luminance intensity of the device decreases to 70 percent of the original value, it is considered the actual end of life as opposed to 50 percent referenced for display applications. "In the area of LEPs, significant research has been in progress to improve material life- times both through the use of materials that are resistant to oxidation and through improved encapsulation," explains Constance. Conducting polymers based on doped polyaniline, conjugated polymer material, and polypyrrole are already demonstrating the stability required for commercial applications, proving the potential for growth and wider accept- ance in the future. Researchers at the Xerox Research Center of Canada recently announced a new polymer in the polythiophene family. This polymer has the best electri- cal properties of any reported plastic semiconductor. Scientists at Xerox's Palo Alto Research Center (PARC) succeeded in jet-printing this material and other polymer semiconductors to make transistors. The jet-printed transistors made this way have matched the performance of the same material deposited by conventional spin-coating (which gives an unpatterned film), showing that the jet-printing process does not adversely affect the performance of the device. The transist