University of Rochester

Chemical Engineer Wins Two Patents for Optoelectronic Materials

March 19, 1997

Samson Jenekhe, a chemical engineer at the University of Rochester, recently won two U.S. patents recognizing his innovative work with plastics that emit or absorb light. The new patents bring to 20 the number he now holds.

The technologies are being commercialized by Research Corporation Technologies (RCT) of Tucson, Arizona. RCT manages hundreds of technologies from research institutions across the country.

The first patent (#5,597,890) is for rigid ladderlike polymers that combine impressive strength with excellent electronic performance in emitting light of all colors.

"These polymers are very stiff and strong because of their shape," says Jenekhe, a professor of chemical engineering, chemistry, and materials science. "If you think of them like a ladder, you can imagine that it's hard to simultaneously break through the two parallel strands held tightly together by the molecular rungs. This structure also makes the polymers extremely resistant to heat: They're durable at temperatures of up to 500 or 600 degrees Centigrade, while most such polymer-based plastics melt or soften at less than 200 degrees."

Jenekhe says that ladderlike polymers' good light-conducting properties make them well-suited for use in next-generation electronic cameras and photocopiers, or for photodetectors that turn lights on automatically. Their sturdiness could also make them useful in heat-resistant coatings for sensitive materials or in membranes used for filtering scalding fluids.

Jenekhe has already incorporated ladderlike polymers into a number of devices, including a light-emitting diode (LED) that glows with the intensity of a television screen. He predicts that many technologies, such as polymer lasers and polymer-based ultra-high-density information storage, might also take advantage of these robust new materials.

Jenekhe's second recent patent (#5,599,899) recognizes his work on conjugated polymer exciplexes, which can convert electricity into flashes of light four times more efficiently than most conjugated polymers. When zapped with light, typical conjugated polymers -- long molecular chains of alternating single and double bonds -- clump together, producing only feeble bursts of light with an efficiency of only about 10 percent. But Jenekhe has found that adding other molecules to the mix to make a molecular "sandwich" can push efficiency as high as 42 percent.

"The added molecules in an exciplex act as buffers," Jenekhe says. "They prevent the conjugated polymers from bunching up and allow them to emit strong light. We've recently found another interesting effect of these added molecules: Different molecules yield different colors of light emitted by the exciplexes."

The conjugated polymer exciplexes are an example of an optoelectronic material, which can turn light into electric signals and vice versa. Laser printers, fax machines, digital displays, computer monitors, fluorescent lighting, and solar cells make use of such materials. Jenekhe's exciplexes produce less heat and are sturdier than conventional conjugated polymers, making them even more attractive for many commercial uses.

While polymer exciplexes have boosted the efficiency of electricity-to-light conversions by an impressive fourfold, this improvement pales in comparison with the increase in efficiency of the opposite reaction: Jenekhe says polymer exciplexes could make the conversion of light to electricity, such as in solar energy converters, up to 1,000 times more efficient.

Jenekhe's research is funded by the Office of Naval Research, the National Science Foundation, and the University's NSF Center for Photoinduced Charge Transfer.