An approach for the control of conjugation length in ppv derivatives

Poly[(2,5-dimethoxy-p-phenylene) vinylene] (DMPPV) of varying conjugation length was synthesized by selective elimination of organic soluble precursor polymers that contained two eiiminatable groups, namely, methoxy and acetate groups. These precursor copolymers with varying composition were in turn synthesized by competitive nucleophilic substitution of the sulfonium polyelectrolyte precursor using methanol and sodium acetate (in various mole ratios) in acetic acid. FT-IR studies confirmed that selective thermal elimination of the acetate groups occurs at 250 °C, leaving the methoxy groups in tact, to yield partially conjugated polymers. Attempts to extend this approach to unsubstituted PPV failed, as the counterion, in this case the chloride, was seen to compete in the nucleophilic substitution process. However, this approach worked well in the case of MEHPPV and a similar control of conjugation lengths was achieved. Preliminary photoluminescence studies of the partially eliminated DMPPV samples showed a gradual shift in the emission maximum from 498 nm to 598 nm with increasing conjugation lengths, suggesting that the color of emission from LED devices fabricated from such polymers can, in principle, be fine tuned.