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 T_g of the composite is 15 °C, which characterizes it as a low-T_g 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 S_n2 of 2±0.2 cm²/kJ at E=50 V/μm than the previously synthesized composite PPT-CZ (n=10):DDCST:C₆₀.