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The performance of photorefractive (PR) polymers strongly depends on the incorporated nonlinear-optical chromophores. We compare three polysiloxane-based PR guest-host polymers with an azo, a stilbene, and a tolane type of chromophore. Characteristic properties such as diffraction efficiency , gain coefficient ⌫, phase shift , modulation of the index of refraction ⌬n, and response time are measured as a function of the external electric field. Orientational enhancement as well as the influence of photoisomerization is observed and analyzed quantitatively. The materials show high performance with ⌬n Ͼ 1 ϫ 10 Ϫ2 , corresponding to external diffraction efficiencies of 60% for samples of only 40-m thickness.a The quantities marked with* refer to E ϭ 100 V/m for the tolane and the stilbene and to E ϭ 80 V/m for the azo composites. The intensity of the writing beams was 1.2 W/cm 2 .

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A variety of new functional materials based on triarylamines, such as low molecular weight glasses which possess hole conducting/photoconductive properties as well as amorphous bifunctional materials which combine photoconductive and non-linear optical (NLO) properties in one compound, have been synthesized. The new hole transporting glasses belong to the class of 1,3,5-tris(triaryldiamino)benzenes (TTADB). The hyperbranched structure and the large aryl groups attached as substituents lead to high glass transition temperatures of up to 141 ¡C in these compounds. The TTADBs do not recrystallize upon cooling from the (T g ) melt, but form stable glasses. Cyclic voltammetry studies reveal multi-oxidation stages for these compounds of which the Ðrst oxidation is reversible. The HOMO energy values determined from CV for TTADB-1 and TTADB-2 are [4.82 and [4.94 eV, respectively. Light emitting diodes with the structure ITO/TTADB-2/Alq3/Al (where ITO \ indium tin oxide) show high efficiency and large current carrying capacity. Further, bifunctional compounds have been synthesized in which a photoconductive moiety such as bis(carbazolyl)triphenylamine or bis(diphenylamino)triphenylamine is covalently bound to di †erent NLO chromophores. Some of these compounds are thermally and morphologically stable amorphous materials, possessing in the range from 85 to 122 ¡C. Cyclic voltammetry measurements reveal that the HOMO energy T g values are between [4.81 and [5.45 eV. In photorefractive measurements using 40 lm thick samples, a di †raction efficiency of 27%, which corresponds to a refractive index modulation (*n) of 3.5 ] 10~3, a maximum two beam coupling gain coefficient (C) of 90 cm~1 and a response time of 40 ms were obtained.

We report on photoelectric and holographic investigations of an organic photorefractive material based on a low molar mass glass with both photoconductive and nonlinear optical properties. By implementing a suitable plasticizer we obtained a composite system which shows extremely fast initial response times down to 450 µs at writing beam intensities of I write ) 10.8 W/cm 2 and 2.5 ms at the canonical intensity of I write ) 1 W/cm 2 . Furthermore, high refractive index modulations up to ∆n ) 6.1 × 10 -3 , long lifetimes and high optical quality of the samples are observed. In comparison to a second similar composite system, which was plasticized by a more polar dopand, we demonstrate the crucial role of this functional constituent on the photoelectric properties. Time-of-flight measurements show a major impact of the plasticizer on the dispersivity of chargecarrier transport. Subsequently the buildup and decay dynamics of the photorefractive grating are substantially affected. Holographic time-of-flight measurements confirm these observations.