It's Not Easy Being Green

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Science  03 Aug 2001:
Vol. 293, Issue 5531, pp. 765
DOI: 10.1126/science.293.5531.765a

If light-emitting diodes (LEDs) made of conducting polymers are fabricated so that there is a large anisotropy in the polymer backbone orientation, either by chain rubbing or by stretching, the emitted light or electroluminesence of the device will often be polarized. At present, the wavelength of the polarized electroluminescence is determined primarily by the chemical structure of the polymer.

Bolognesi et al. have succeeded in making an LED with a color output that can be adjusted. This device is made from two polymers, a green emitter [poly(p-phenylenevinylene) or PPV] and a red emitter {poly[3-(6-methoxyhexyl)thiophene] or P6OMe}, that are prepared as films with their backbones oriented orthogonally to each other. At low voltages (<7 volts), only P6OMe is excited, and a red emission is observed. As the voltage increases, the emission from PPV grows rapidly, and the color becomes orange-green. Because the orientation of the two materials is orthogonal, the emitted light has orthogonal polarization. Thus, the color can be changed by rotating a polarizing filter, allowing the color to be tuned from red to green. — MSL

Adv. Mater.13, 1072 (2001).

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