Aryl-substituted PPVs

A critical criterion for emissive polymers for LEDs is their stability, which determines the device lifetime. The major problem is the susceptibility of extended conjugated systems to attack by oxygen and/or water, which cannot be totally excluded even by the best device encapsulation techniques [130], In PAVs, the most vulnerable sites are the vinylene moieties. These could be protected by direct attachment of electron-withdrawing groups to them, but this is not always possible and may have undesirable effects upon the emission color. Generally speaking the use of less electron-rich arylene units seems to be the best approach so that the aryl-substituted PPV 53 is stable enough to be used commercially in LEDs. This material is also one of the most defect-free PPVs known, which also... 

A complete different route to PPVs [84] starts from tetrahalogenated xylylen-derivatives and by an dehalogenation reaction yielding aryl substituted PPVs. 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

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