The Photopolymerization and Cross-Linking of Electroluminescent Liquid Crystals Containing Methacrylate and Diene Photopolymerizable End Groups for Multilayer Organic Light-Emitting Diodes

Light-emitting liquid crystals incorporating two photopolymerizable end groups have been synthesized for implementation in multilayer organic electroluminescent devices. Series of diene as well as diallylamine and methacrylate moieties are used as the photoreactive groups attached via spacers to both ends of a fluorene-based chromophore. Nematic glasses are formed upon cooling from the liquid crystalline phase. Ultraviolet radiation at room temperature is used to photopolymerize and cross-link the reactive units, resulting in the formation of insoluble nematic polymer networks. The quantum efficiency of photoluminescence from the fluorene-based chromophore is increased by cross-linking of the diene reactive end groups. Photopolymerization occurs more rapidly with methacrylate end groups, but the chromophore is somewhat degraded by the incident radiation. In materials incorporating the photopolymerizable 1,4-pentadien-3-yl group, the formation of the polymer network enhances the electroluminescence. An electron-transporting polymer containing an oxaziaole ring is deposited on top of the insoluble network. Electroluminescence is obtained with an unchanged spectrum.