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15 October 2004 Light-emitting materials based on liquid crystals
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Liquid crystal (LC) materials with negative dielectric anisotropy have been successfully applied to light emitting diode. Even for a nematic phase, the Fredericks transition was avoided under such a strong electric field as used in organic light emitting diode (OLED). The LC materials having shallower highest occupied molecular orbital (HOMO) levels have been emissive due to their higher probability for hole injection. The LC materials incorporated three fluorescent dyes for each color (R,G,B) show corresponding color emission. However, only blue dye shows extraordinarily small light emission. Relative fluorescence quantum yield measurement reveals similar fluorescence efficiency for all dyes. Only blue dye’s HOMO level lies very close to that of the matrix LC. This fact may lead to very small hole trapping probability for the blue dye molecule. It is suggested that in the OLED system using LC materials studied here, the recombination of the electrons and the holes trapped at the dye molecules is dominant for light emission rather than Foerster energy transfer.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Masayoshi Suzuki, Hiromoto Sato, Peer Kirsch, Atsushi Sawada, and Shohei Naemura "Light-emitting materials based on liquid crystals", Proc. SPIE 5518, Liquid Crystals VIII, (15 October 2004);

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