Poly p-Phenylene Vinylene Copolymers with Electron Donor and Aryl Substituents

1 Poly(p-Phenylene Vinylene) Copolymers with Electron Donor and Aryl Substituents 

Due to higher variety of possible structures, copolymers allow a better control of the HOMO LUMO levels necessary to optimize the EL properties of the PPV, compared to homopolymers. Often the optical and electronic properties in copolymers can be finely tuned by simply changing the feed ratio of comonomers (although the structure-property relationship in these systems is even more complex than in homo-PPV polymers). Using different comonomer units, various PPV-based materials with tuned optical and electronic properties have been prepared. 

Although MEH-PPV 13 (at the time of discovery) was one of the most efficient soluble polymers for PLEDs application, its performance is not high enough for commercialization as LEP. One of the reasons is unbalanced hole-electron mobility in MEH-PPV (the mobility of holes is 100 times faster than the mobility of electrons) [133]. Copolymerization with other conjugated monomers, to some extent, can improve the electron-transporting properties and increase the EL performance. 

The first realization of this approach was reported by the Cambridge group, which synthesized copolymers 80 containing phenylene vinylene and dialkoxy(phenylene vinylene) units by the thermoconversion method [23,134], A 30-fold improvement in EL efficiency was observed for these copolymers compared with PPV 1 or MEH-PPV 13 devices fabricated in the same configuration (Chart 2.15). 

SCHEME 2.15 Dependence of the electroluminescence of alkoxyphenyl-PPV copolymers on the comonomers ratio (PLED configuration ITO/PEDOT or PANI/polymer/Ca or Yb/Ag). 

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