Increasing of stability depended on the position of alkoxy group in PPV

In order to prevent the photo oxidation of the vinylene group of poly(p-phenylenevinylene) (PPV) series, the poly(p-phenylenedifluorovinylene) (PPDFV) derivatives with difluoro groups on vinylene unit were synthesized by Gilch polymerization using potassium tertbutoxide. The stability of the PPDFV backbone is attributed to the electron-withdrawing effect of the fluoro groups which prohibit the initial step of [2+2] cycloaddition for the oxidation of the vinylene unit. In photo-degradation experiments with white light, the PL spectra of m-EHOPh-PPDFV film is blue shifted about 19 nm and the optical density of the side peak at 380 nm is increased to 0.5 atomic unit. In case of p-EHOPh-PPDFV, the PL spectra show almost same maxima peaks at 448–450 nm after irradiation from 1 h to 5 h. p-EHOPh-PPDFV with para-alkoxy phenyl group shows very stable PL spectra against photo oxidation as compared to the case of m-EHOPh-PPDFV with meta-alkoxy phenyl group.