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Electroluminescence in conjugated polymers was first discovered in poly(p-phenylenevinylene) (PPV)1. Since then research efforts on polymer-based light emitting devices have increased dramatically, primarily due to their potential application in full color flat panel displays and the low fabrication costs associated with this technology. Poly(phenylenevinylene) (PPV) and its derivatives have been widely used as emissive materials in polymer light emitting diodes (PLEDs). Conjugated polymers derive their semiconducting properties from delocalized It- electrons along the polymer chain. Therefore it is possible to modify the semiconducting properties of the polymer by adding different functional groups to the polymer structure thereby altering the extent of delocalization of the rc-electrons. The knowledge of how different functional groups in the PPV structure affect its physical properties is very important for understanding the structure-property relationship in this material. However, a broad molecular weight distribution and the presence of blocks with different conjugation lengths in the polymeric material often complicate the issue. In this sense, oligo(phenylenevinylene) (OPV) type of material is ideal to use as a model system to study the structure-property relationship. Due to controllable and well-defined chemical structures, it is much easier to follow and correlate the physical properties of the OPVs with the molecular structures. In addition, many oligomeric materials can be thermally sublimed under high vacuum, allowing for the preparation of multilayer organic light emitting diode (OLED) structures and devices in an ultra-clean and well-controlled environment thus overcoming the uncertainties involved in wet processes.
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