Efficient full color electroluminescence and stimulated emission with polyphenylenes

We demonstrate the fabrication and characterization of highly efficient red-green-blue (RGB) and white light emitting devices based on poly(phenylene) type materials as the hexaphenyl and the methyl substituted laddertype poly(para-phenylene) (m-LPPP). The RGB-devices are fabricated with an external color conversion technique based on PHP, whereas the white light emission is generated by an internal excitation energy transfer (Forster-type) from the blue m-LPPP component to a red light-emitting polymer in a polymer blend, which is used as the active layer in a light-emitting diode. We present photophysical properties, like spectral line-shape site selectivity of photoluminescence (PL), and electroluminescence of bulk poly(para-phenylenevinylene) PPV films and isolated PPV chains incorporated into a self-assembled matrix ordered on a nanometer scale. The ordering is a result of the lyotropic liquid-crystalline character of a matrix material, which leads to the formation of a regular hexagonal array of channels with a diameter of about 15 Angstrom, in which the conjugated polymer chains are contained. The structure of the nano-composite is confirmed by X-ray diffraction analysis. The application of the nano-composites in organic-light-emitting-diodes is presented. Furthermore we show that poly(para-phenylene) derivatives are suitable for realizing optically pumped lasers. A suitably structured m-LPPP waveguide shows a spectrally very narrow high directional blue-green light output when optically pumped. The high optical gain of m-LPPP is a result of the spectral separation of stimulated emission and photoinduced absorption bands, thus spectral narrowing is even observable in below cut-off waveguides. Under resonant excitation conditions, we observe strong stimulated Raman scattering.