Nematic-like mesophase photoconductive polymer for photorefractive applications

A new nematic-like mesophase photoconductive polymer PPT–TPA consisting of wholly aromatic rigid backbone of poly(p-phenyleneterephthalate), PPT and pendent hole-transporting triphenylamine (TPA) groups attached to the ends of oxydecyl spacers has been synthesized. The photorefractive composite contains the photoconductor PPT–TPA, the chromophore diethylaminodicyanostyrene (DDCST), and the photosensitizer C60. Although no plasticizer was added, the glass transition temperature Tg of the composite is 15 °C, which characterizes it as a low-Tg photorefractive material. We investigate the correlation between the mesophase structure and its optical/physical properties by X-ray diffraction, photoconductive and photorefractive experiments. The new composite and its properties are compared to PPT–CZ composites with only a different charge transporting agent (carbazole, CZ) but a much more ordered mesophase structure, which were studied previously and have shown very good photorefractive properties. Despite of a lower photoconductivity of the new photorefractive composite PPT–TPA (n=10):DDCST:C60 this material shows a higher photorefractive sensitivity Sn2 of 2±0.2 cm2/kJ at E=50 V/μm than the previously synthesized composite PPT–CZ (n=10):DDCST:C60.