Tailor Pi-Conjugated Polymers for Enhanced Luminescence Efficiency

Abstract

Abstract : During the reporting period, we have systematically examined the role of a meta-phenylene in the tt-conjugated polymers. Resulting form its effective tt-conjugation interruption, controllable insertion of m-phenylene along the polymer backbone is demonstrated to be a useful tool for precise color tuning. Introduction of a bent angle at the m-phenylene unit also improves the molecular packing in the solid state, thereby enhancing the PL quantum efficiency in the solid state. Although original investigation is focusing on the poly(phenylene ethynylene) system, the concept has been successfully extended to poly(phenylene vinylene) system. By synthesis of polymers with defined chemical structures, we have investigated the impact of trace iodine to the luminescent properties of polymers. The results show that the Wittig-Horner reaction is a preferred method to construct the vinylene bond of trans-configuration. It is noted that there are two types of phenyl rings, i.e., m- and p-phenyl rings, present along the PPV chain examined. Selective placement of substitute on the different type of phenyl rings is found to significantly affect the luminescent properties of the polymers. Through collaboration with Professor Karasz's group at UMass, many of the polymers are shown be electroluminescent with EL efficiency reaching as high as 1 % The EL efficiency of this class of materials will be further increased by improving the charge injection within the polymer layer.