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How hot was it?

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2:02pm, September 13, 2005

From Washington, D.C., at a meeting of the American Chemical Society

Scientists have created heat-sensing polymers that indicate exposure to high temperatures by changing color under ultraviolet (UV) light. If built into food and medicine packaging, such materials could serve as indicators of spoilage.

At the heart of the sensitive polymers are photoluminescent dyes, explains Chris Weder, a polymer chemist at Case Western Reserve University in Cleveland. Individually, each fluorescent-dye molecule emits a specific visible wavelength—a color—when zapped with UV light. When two or more dye molecules are close enough together, however, they redistribute this incoming energy among themselves and emit a color different fro

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